Seismic Response of Building Façade System with Energy ... · Seismic Response of Building Façade System with Energy Absorbing Connections iv 2.6 Performance based earthquake engineering

Seismic Response of Building Façade System with Energy Absorbing Connections

Rahila Wardak Hareer

A thesis submitted for the degree of Doctor of Philosophy

Centre for Built Environment and Engineering Research Queensland University of Technology

October, 2007


i

Abstract

Facades are popular in modern buildings and are made of different materials such as pre-cast concrete, glass, aluminium, granite or marble and steel. During recent times seismic activity in densely populated areas has resulted in damage and a consequent loss of life. There were many types of building failure, including failure of building facade systems. Facade systems are highly vulnerable and fail more frequently than the buildings themselves with significant devastating effects. During an earthquake building frames suffer large interstorey drifts, causing racking of the building facade systems. The facade systems may not be able to cater for such large deformations and this can result in either functional or total failure at the facade connections or damage by pounding (impact) with adjacent facade panels. Facade failure and collapse can cause serious damage to buildings and injury to people in the vicinity. Moreover, facade represent between 10– 20 % or more of the total building cost depending on the size and importance of the facility and facade material (Facades1980). Considering the cost and safety issues, the importance of a well designed facade system on a building needs to be emphasised. In modern buildings, energy absorbing passive damping devices are very commonly used for energy absorption in order to manage the vibration response of multistorey buildings in an earthquake event. A number of manufactured dampers such as Viscoelastic and viscous, friction and yielding dampers are available. These dampers use a range of materials and designs in order to achieve diverse levels of damping and stiffness.

This thesis is an investigation of the seismic behaviour of building facade systems and studies the effects of facade and connection properties on this response. The objectives with energy absorbing connections of the study are to determine and control facade distortions and to establish the required connection properties. Finite Element techniques have been used for modelling and analysis of the building frame, facade and connections. Time history analyses under earthquake loadings were carried out to determine the system response in terms of inter-storey drifts, facade distortions, differential displacement between facades and frames and the axial force in horizontal connections. Connection properties with respect to stiffness and energy absorption capability (or damping) have been modelled and varied to obtain the desired response. Findings illustrate the influence of these connection properties on system response and show that it is possible to control facade distortions to within acceptable limits. They also demonstrate that energy absorbing connections are able to reduce inter-storey drifts and mitigate the detrimental seismic effects on the entire building facade system.

Keywords

Earthquake; facades; buildings; time histories; connection; stiffness; damping; inter-storey drift; distortion; finite element.


ii

Publications

International Refereed Conference Papers:

“Energy Dissipation and Behaviour of Building Facade System under Seismic Load” Proceedings of the Ninth International Conference on Civil and Structural Engineering Computing, Egmond-aan-Zee, The Netherlands, September 2003.

“Energy Dissipation and Behaviour of Building Facade System under Seismic Load” Proceedings of the Eight International Conference on Computational Structures Technology, Las Palmas De Gran Canria, Spain, September 2006.


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Contents

Abstract i

Keywords i

Publications ii

Contents iii

List of Figures viii

List of Tables xiv

Symbols xv

Abbreviations xvi

Statement of Original Authorship xvii

Acknowledgements xviii

CHAPTER 1 INTRODUCTION 1

1.1 Background to the Study 2

1.2 Research Problem 4

1.3 Aims and Objectives of research and investigation 6

1.4 Method of Investigation 6

1.5 Scope of Research 7

1.6 Layout of Thesis 8

CHAPTER 2 LITERATURE REVIEW 11

2.1 Introduction 12

2.2 Facades and facade connections 16

2.3 Earthquakes in Australia 17

2.4 Design methods 19

2.5 Current code requirements 22


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2.6 Performance based earthquake engineering 24

2.7 Basic components of facade connection systems 24

2.8 Common or conventional facade connection systems 25

2.9 Advanced facade connections 30

2.10 Design criteria for advanced facade connections 30

2.10.1 Friction mechanism 31

2.10.2 Composite material mechanism 31

2.10.3 Torsional mechanism 33

2.10.4 Flexural mechanism 33

2.11 Interaction between structure and facade 35

2.12 Viscoelastic (VE) dampers 36

2.13 Research on seismic effects on facade 38

2.14 Conclusions to the literature review 48

2.14.1 Summary of the literature review 48

2.14.2 Proposed research 50

CHAPTER 3 DEVELOPMENT OF COMPUTER MODEL & BUILDING FAÇADE SYSTEM

51

3.1 Introduction 52

3.2 Description of 12-storey structural models-undamped structure 52

3.2.1 Properties of the building façade connection 54

3.2.2 Description of 12-storey structural model with energy absorbing connection

54

3.3 Material properties 56

3.4 Loading and boundary conditions 57

3.5 Input earthquake records 57

3.6 Finite element analysis 59

3.7 Verification of results 60


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3.7.1 Model calibration 61

3.7.2 Results of analytical investigation using the parameters of Pinelli et. al

64

3.7.3 Results of analytical investigation using the optimum values of connections properties spring stiffness (kd = 20,000 kN/m) and dashpot damping (cd = 35,000 kN/m)

64

3.8 Analysis of 3-storey building façade system and feasibility study 66

3.8.1 Description of 3-storey structural model 66

3.9 3-storey building façade system structural model 66

3.9.1 Description of 3-storey structural model - undamped structure 67

3.9.2 Description of 3-storey structural model with energy absorbing

connection

68

3.10 Seismic responses of 3- storey undamped structure with precast concretre façade -effect of spring stiffness

68

3.11 Seismic responses of 3- storey structure with precast concrete façade effect of energy absorbing connection

69

3.12 Seismic responses of 3- storey structure with precast concretre façade undamped structure and structure with VE connections

73

3.13 Seismic responses of 3- storey undamped structure and structure with VE connections –under higher seismic loads

83

3.14 Seismic responses of 3- storey structure with glass facades-effect of spring stiffness and dashpot damping

85

3.15 Summary of finding 89

CHAPTER 4 ANALYSIS OF 6-STOREY BUILDING FAÇADE SY STEM 93

4.1 Introduction 94

4.2 6-storey building façade system 94

4.2.1 Description of 6-storey structural models 94

4.3 Seismic response of 6-storey structure for load case 1 95

4.4 Seismic response of 6-storey structure for load case 2

105


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4.5 Seismic response of 6-Storey building façade system for load case 2: Effects of Façade Mass (undamped structure)

110

4.6 Summary of findings 115

CHAPTER 5 ANALYSIS OF 12-STOREY BUILDING FAÇADE SYS TEM 117

5.1 Introduction 118

5.2 Seismic response of 12-storey building façade system with precast concrete façade for load case 1

118

5.3 Seismic responses of 12-storey building façade system for load case 2 126

5.4 Seismic responses of 12-storey undamped structure and structure with VE connections under higher seismic loads

134

5.5 Seismic responses of 12-storey structure with precast concrete façade- effect of damping to stiffness ratio

141

5.6 Seismic analyses of 12-storey building façade system for load case 2- effect of façade mass

144

5.7 Seismic responses of 12-storey building with glass façades for load case 1

147


CHAPTER 6 ANALYSIS OF 18- STOREY BUILDING FAÇADE SYSTEM

155

6.1 Introduction 156

6.2 18-storey building façade system 156

6.2.1 Description of 18-storey structural models 156




CHAPTER 7 CONCLUSIONS AND RECOMANDATIONS 179

7.1 Contribution from this Research 180


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7.1.1 3-storey building façade system 182




7.1.5 Conclusion 189

7.2 Recommendations for Further Research 190

LIST OF REFERENCES 191

APPENDIX

A Seismic responses of 3 storey building facade system 199

B Seismic responses of 6 storey building facade system 201

C Seismic responses of 12 storey building facade system 207

D Seismic responses of 18 storey building facade system 215


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List of Figures

Figure 1.1 Earthquake in Klaten, Java – Indonesia, May 2006. 4

Figure 2.1 Modern buildings provided with façade system 13

Figure 2.2 Extensive earthquake damages in Newcastle 19

Figure 2.3 Typical façade connection components 25

Figure 2.4 Load bearing connection 28

Figure 2.5 Typical configuration of façade system 29

Figure 2.6 Steel-Rubber composite 32

Figure 2.7a Ductile inserts 32

Figure 2.7b Ductile Loop 32

Figure 2.7c Double taper flexure 32

Figure 2.7d Single taper flexure 32

Figure 2.8 Conceptual Torsion Connector 33

Figure 2.9 Ductile Loop Connection 34

Figure 2.10 Advanced tapered façade connection 34

Figure 2.11 Idealized force-displacement loop of VE devices 36

Figure 2.12 Typical VE solid damper 37

Figure 2.13 1/4-Scale Building design model 41

Figure 2.14 A 20-storey baseline building 42

Figure 2.15 Schematic representations of fundamental vibration modes 45

Figure 2.16 Details of selected spandrel façade type 47

Figure 3.1 Model of twelve storeys building façade system 53

Figure 3.2 Typical L shaped connection 54

Figure 3.3 Typical VE solid damper 56

Figure 3.4 El-Centro earthquake record 58

Figure 3.5 Kobe earthquake record 58


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Figure 3.6 Northridge earthquake record 59

Figure 3.7 NCEER 1/4-scale building design model 62

Figure 3.8 Upper floor displacement of structure with no tie-back connections and structure with advanced connections

63

Figure 3.9 Upper floor displacement for structure with no tie-back connections

65

Figure 3.10 3-storey concrete frame 66

Figure 3.11 3-storey concrete frame with façade panels 67

Figure 3.12 3-storey building façade system with spring-dashpot connections 68

Figure 3.13 3-Storey structure with and without VE damping connections, time histories of deformation in upper and lower connection of façade

74

Figure 3.14 3-Storey structure with and without VE damping connections, time histories of force in upper and lower connection of facade

75

Figure 3.15 3-Storey structure with and without VE damping connections, time histories for differential displacement between frame and façade

76

Figure 3.16 3-Storey structure with and without VE damping connections, time histories of distortion of façades

77

Figure 3.17 3-Storey structure with and without VE damping connections, maximum deformation in connection

79

Figure 3.18 3-Storey structure with and without VE damping connections, maximum forces in connections

80

Figure 3.19 3-Storey structure with and without VE damping connections, maximum differential displacement between frame and façade

81

Figure 3.20 3-Storey structure with and without VE damping connections, maximum distortion of façade

82


84


85

Figure 4.1 Model of six storeys building façade system 95

Figure 4.2 6-Storey structure with and without VE damping connections, maximum deformation in connections

97


x

Figure 4.3 6-Storey structure with and without VE damping connections, maximum force in connections

98


99

Figure 4.5 6-Storey structure with and without VE damping connections, maximum interstorey drift

100


101

Figure 4.7 6-Storey structure with and without VE damping connections, maximum deformation of connections

102


103

Figure 4.9 6-Storey structure with and without VE damping connections, maximum differential displacement between façade and frame

104


104

Figure 4.11 6-Storey structure with and without VE damping connections, maximum deformations of connections

106


107


108


109

Figure 4.15 6-Storey structure with and without VE damping connections, maximum distortion of facade

109

Figure 4.16 6-Storey structure with and without VE damping connections, maximum deformations in connections

111


112

Figure 4.18 6-Storey structure with and without VE damping connections, maximum interstorey drifts

113


113

Figure 4.20 6-Storey structure with and without VE damping connections, 114


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maximum distortion of façade

Figure 5.1 12-Storey structure with and without VE damping connections, maximum deformations in connection

120

Figure 5.2 12-Storey structure with and without VE damping connections, maximum force in connection

120

Figure 5.3 12-Storey structure with and without VE damping connections, maximum differential displacements

121


122


123


124


124


125


126

Figure 5.10 12-Storey structure with and without VE damping connections, time histories of deformation in upper and lower connection of façade

127

Figure 5.11 12-Storey structure with and without VE damping connections, time histories of differential displacement between frame and façade

128

Figure 5.12 12-Storey structure with and without VE damping connections, time histories of distortion of façade

128

Figure 5.13 12-Storey structure with and without VE damping connections, maximum deformations in connection

129

Figure 5.14 12-Storey structure with and without VE damping connections, maximum forces in connection

130

Figure 5.15 12-Storey structure with and without VE damping connections, maximum differential displacement

131


132


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Figure 5.17 12-Storey structure with and without VE damping connections, maximum distortion of façade.

133

Figure 5.18 12-Storey structure with and without VE damping connections, maximum deformation

135


136


138


139

Figure 5.22 12-Storey structure with and without VE damping connections, maximum distortion of façades

140


144

Figure 5.24 Differential displacement in 12-storey structure –effect of façade mass.

146


148


149


149


150

Figure 5.29 12-Storey structure with and without VE damping connections, maximum deferential displacement between upper and lower façade

151

Figure 6.1 Model of 18-storeys building façade system 157

Figure 6.2 18-Storey structure with and without VE damping connections- maximum deformation in connection

159


160


162


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Figure 6.5 18-Storey concrete frame with and without VE damping connections, maximum distortion of façade

164


165

Figure 6.7 18-Storey structure with and without VE damping connections (horizontal direction), maximum deformation in connection

166

Figure 6.8 18-Storey structure with and without VE damping connections (horizontal direction), maximum force in connection

167

Figure 6.9 18-Storey structure with and without VE damping connections (horizontal direction), maximum differential displacement between façade and frame

168

Figure 6.10 18-Storey structure with and without VE damping connections (horizontal direction), maximum distortion of façade

168


170

Figure 6.12 18-Storey structure with and without VE damping connections - maximum force in connection

171


173

Figure 6.14 18-Storey structure with and without VE damping connections, maximum interstorey drifts

174


175


xiv

List of Tables

Table 3.1 Comparison of maximum (upper floor) deflection 66

Table 3.2 Natural frequencies of 3-storey structure. 67

Table 3.3 Maximum values of the response quantities, considering horizontal connections stiffness

69

Table 3.4 Maximum values of the response quantities, considering connections stiffness kd and damping coefficient cd

71

Table 3.5 Maximum values of the response quantities considering connections stiffness kd and damping coefficient cd

72

Table 3.6 Maximum values of the response quantities, considering connections stiffness

87

Table 3.7 Maximum values of the response quantities considering connections stiffness and damping coefficient

87

Table 3.8 Maximum values of the response quantities, considering connections stiffness and damping coefficient

88

Table 4.1 Natural frequency of 6-storey structure 95


Table 5.2 Maximum values of response quantities considering connections stiffness kd and damping coefficient cd

142

Table 5.3 Maximum values of response quantities considering connections stiffness kd and damping coefficient cd

143

Table 5.4 Maximum values of the response quantities considering façade mass ratio

147



xv

Symbols

A Shear Area

Cd Damping Coefficient of VE Damping Device

f Magnification Factor

fc’ Compressive Strength

Ec Young’s Modulus

F Overall Force

Fp Seismic Force applied to a Component of a Building or equipment at its Centre of Gravity

G Gravity Load

G’ Viscoelastic Damper Shear Storage Modulus

G” Viscoelastic Damper Shear Loss Modulus

h Height above the Structural Base of the Structure to Level x

kd Axial Stiffness of Damping Device

k Stiffness

m Lumped Mass

M Total Mass Matrix of the Structure

Q Live Load on the Structure

Rw Over Strength and Ductility Factor that is Associated with the Lateral Load-Resisting System

t Temperature

t Thickness of Viscoelastic Material

T Natural Period

γ Shear

ρ Density

υ Poisson’s Ratio

ω Circular Frequency


xvi

Abbreviations

ATC

CWCT

SEAOC

ASCE

AEES

EDD

FEA

FEM

EICWS

NEIC

NIST

PCI

PGA

UBC

USGS

VE

Applied Technology Council

Center for Window and Cladding Technology

Structural Engineering Association of California

American Society of Civil Engineers

Australian Earthquake Engineering Society

Energy Dissipation Device

Finite Element Analysis

Finite Element Method

Earthquake Isolated Curtin Wall System

National Earthquake Information Center

National Institute of Standards and Technology

Precast Concrete Institute

Peak Ground Acceleration

Uniform Building Code

U.S. Geological Survey

Viscoelastic


xvii

Statement of Original Authorship

The work contained in this thesis has not been previously submitted for a degree or diploma at any higher education institution. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made.

Signature

Date

Seismic Response of Building Façade Systems with Energy Absorbing Connections

xviii

Acknowledgement

I am grateful and indebted to my supervisors Prof. David Thambiratnam and Adjunct Professor, Nimal Perera as associate supervisor for their unlimited support and supervision and encouragement throughout the course of this study. Their insight and excellent suggestions were extremely important in finalizing this thesis.

I would like to thank Queensland University of Technology and the Centre for Environment and Engineering Research for providing Postgraduate Research Scholarship to carry out my research project. I would also like to thank the Physical Infrastructure Centre and the Faculty of Built Environment & Engineering for providing financial and technical support. Thanks are extended to the members of the reading committee for their helpful advice. It is pleasure to thank fellow post-graduate students and friends for their support and contribution to this research with whom I shared the ups and downs of completing this research project.

Finally I wish to express my gratitude to my family for their support, encouragement, and patience. Without their love and support this venture would have been impossible.


1

Chapter 1

Introduction


2

1. Introduction

1.1. Background to the study

Earthquakes are the least understood of natural hazards and are one of nature’s

biggest dangers to life on earth. They are considered to be one of man’s most feared

natural phenomena, as they give very little or no warning before occurring (Dowrick,

1977). Damage resulting from earthquakes can be enormous in many respects, but

particularly in terms of loss of lives and financial costs.

During recent years there has been an increase in the incidents of large earthquakes

occurring in very high population areas. They have caused severe damage and in

several case the complete destruction of multi-storey buildings as well as countless

deaths. To date, in 2006 alone there were 3 major earthquakes, all of a magnitude

7.7- 8 on the Richter scale: Koryakia, Russia 205 km North East of Il'pyrskiy,

Russia; Tonga, 2150 km North Northwest of Auckland, New Zealand; and Java, 25

km South Southwest of the Indonesian city of Yogyakarata, with similar

consequences. (Earthquake Hazards Program, U.S. Geological Survey, (USGS)

Earthquake Information for 2006). These earthquakes all occurred in densely

populated areas and caused massive damage to buildings, infrastructure and resulted

in loss of lives. Many types of building failures including the failure of building

facade systems were involved. Figure 1.1 shows typical building collapse after an

earthquake in Klaten.

For many years, it had been a common misconception that facades should be

considered as non-structural elements of a building. However, throughout the past

two to three decades, a number of investigations in this area have confirmed that

facades indeed have structural contributions to the lateral stiffness of buildings.

There are now sufficient analytical and experimental results that can verify the

ability of facades to have significant influences on the response and behaviour of

buildings during earthquakes. Facades are common in modern buildings and can be

made of different materials such as precast concrete, glass, steel, aluminium and

brick. These facade systems are highly vulnerable and fail more frequently than the

buildings themselves with significant and devastating effects during earthquakes

(Goodno, Craig, and Wolf 1987-1989). Precast concrete facades in particular, have


3

become a major concern to engineers, due to their larger weight, stiffness and the

techniques used for their attachment to buildings. During an earthquake, the

behaviour of the facade will be dictated by the cyclic interaction between the panels

and the supporting primary structure, and typically the facade and connections are

simultaneously subjected to three primary effects:

i. Inertia forces generated by the acceleration of the panel, transmitted from the

panel to the main structure via shear loading of the connectors.

ii. Horizontal inter-storey drift resisted by the panels which results in horizontal

shear forces in the connection.

iii. Gravity load of the panel which is supported by the bearing connections.

The success of facade systems has been related to the ability of the facade

connections both in meeting strength requirements and just as importantly meeting

ductility requirements (Iverson, 1986). Often the response to establishing ductility

has been to increase strength requirements to a level where only elastic action is

likely to occur. Current seismic design is based on using pseudo-static forces to size

members and connections. A further factor that often complicates the design of the

facade is that much of the construction utilizes steel frames. Increasingly, ductility

demand and flexibility of building structures have complicated the design of facade

connections even more.

The primary difference in the design of facades in seismic and non-seismic regions is

that in seismic design, inter-storey deformation resulting from inelastic response of

the building frame (as high as 4 times the elastic response) needs to be

accommodated. The seismic behaviour of the building frame–facade system is

influenced by the dynamic properties of the structural members, namely the frame,

facade, facade connection and the properties of the earthquake. A particular facade

and connecting system which performs well when attached to a certain frame under a

particular earthquake may respond differently when attached to another frame or

subjected to different earthquake forces. This is because facade-connection

properties may not be compatible with the dynamic characteristics of the building

and earthquake. Moreover, facade and connection properties influence the seismic

response of the system.


4

Figure 1.1 Earthquake in Klaten, Java – Indonesia, May 2006. (Based on USGS, 2006)

1.2. Research Problem

During an earthquake, building frames suffer large inter-storey drifts, causing

racking of the building facade systems. The facades which are attached to the

building need to travel with the frame with minimal distortions. The facade systems

may not be able to take up such large deformations and this can result in failure at the

connections or failure by pounding (repeated impact) of adjacent members. There

have been numerous facade failures (Sutter 1976, Dreger 1989) especially in an

earthquake event (Goodno, Craig, and Wolf, 1987-1989). Facade failure and collapse

can cause serious damage to buildings and injury to people in the vicinity. In

addition, even small scale damage to facade sealants, has an impact on thermal and

weather insulation. The cost of the facade will vary due to its materials, size and the

importance of the facility. For example, marble or granite facades could cost

approximately 10 to 20% or more of the total cost of a building .However, the cost of

replacing or repairing building facades adds significantly to original costs estimates.

In addition, failure of the facade in an earthquake event, will involve a risk of injury

to the public. For these reasons facade failure needs to be minimised or if possible

avoided.

With these in mind, a comprehensive research project on the seismic response of

building façade system was undertaken. This research project models and analyses

halla

This figure is not available online. Please consult the hardcopy thesis available from the QUT Library


5

building facade systems with energy absorbing connections. The parameters treated

in this project are:

i. 4 Structural models (3, 6, 12 and 18 storey buildings)

ii. 2 Different load cases

iii. 3 Different earthquake records

iv. Different connections properties (and optimum values)

v. Facade types and influence of mass

To establish feasibility and define parameters, firstly a simple three storey single bay

concrete frame fitted with facades in the second and third storey was analysed under

three different earthquake excitations. The effect of the connection stiffness on the

seismic response of the structural system was investigated. The effectiveness of

energy dissipating connectors placed horizontally between the facade and the

building frame was then investigated. Optimum values of the energy absorber

connection were found. Viscoelastic (VE) damping connections have been used for

the first time. To extend the proposed approach, three additional structural models,

namely 6-storey, 12 storeys and 18 storey building facade system with embedded

damping systems have also been studied. Finite element techniques with time history

analysis investigated the influence of connection stiffness and damping capacity,

mass of facade (and hence material type), dynamic properties of the building frame

(in terms of its natural periods) and the dominant periods and intensity of the

earthquake.

Fundamental research on the seismic response of building facade systems carried out

in this project generated information to develop design guidelines for controlling the

response through connection systems. These are expected to provide optimum

designs for connections, thereby minimising facade failure during seismic events.

For the purposes of this study, the program selected for the numerical analysis was

SAP2000. This program models and solves a wide range of linear and non-linear

problems involving the static and dynamic response of systems.

This research studied the effectiveness of damping systems in mitigating seismic

response for each structure, based on the following parameters.


6

i. the deformation of connections (in terms of extension/compression of spring)

ii. the axial forces in springs

iii. the differential displacement between facade and frame

iv. the distortion of facade

v. the differential displacement between upper and lower storey facade

vi. the interstorey drift

The results of the above parameters were determined and compared with those of

undamped structure. In addition the optimum values for spring stiffness and dashpot

damping were obtained.

1.3. Aims & Objectives of Research and Investigation

The main aim of this project was to generate fundamental research information on

the seismic response of building-facade systems where passive damping devices

have been installed within facade panels. The project also has the following

additional objectives:

i. To set up finite element models of the building facade system (BFS), which

can be used for investigation under different conditions.

ii. To determine facade connection properties with respect to stiffness and

energy absorbing capability (or damping) which provide efficient seismic

response of the facade (minimise deformation) and their optimum values of

connection properties.

iii. To establish the influence of important parameters such as building height,

loads, facade type and mass as well as earthquake type and peak ground

acceleration (PGA) on the facade response (deformation).

iv. To develop connection design information this will minimise facade failure

during earthquakes.

1.4. Method of investigation

The research methods listed below were mainly based on analytical modelling using

finite element techniques.


7

• The major portion of the research was carried out using computer

simulations. Finite element models of the building facade system was set up

and analysed under three different earthquake excitations.

• The damping mechanisms were modelled as a linear spring and dashpot in

parallel for the VE damper, to establish the desired properties.

• Size and material properties of the structure, damping properties,

configuration and location of dampers, facade mass, and earthquake types,

(identified with respect to dominant periods), dynamic properties of the

building frame (identified with respect to stiffness, mass and hence natural

periods of vibration) were parameters in the investigation and the influence of

these were studied.

• Establishment of optimum facade-connection properties.

• Evaluation of results and reporting major findings.

1.5. Scope of research

This research investigates the seismic response of building facade systems with VE

dampers. The main response parameters are the deformation of connections, the axial

forces in connection, the differential displacement between facade and frame, the

distortion of facade, the differential displacement between upper and lower storey

facade and the interstorey drift of each structure in the three different earthquakes.

The scope of this investigation is as follows:

i. Building structures

a. Building facade system is between 12 m to 72 m in height

b. The structures have natural frequencies within the range of dominant

frequencies of the earthquakes treated.

ii. Damping mechanisms

a. Viscoelastic dampers are considered

iii. Energy absorbing connection locations

a. VE damping connections are installed horizontally at four points on

each floor panel to frame.


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iv. Seismic records

a. Three different earthquakes, each with a different duration of strong

motion and range of dominant frequencies, were used. All the seismic

records were scaled to have the same peak ground accelerations to

facilitate comparison and to suit Australian (low) seismic conditions.

The comprehensive investigations treating all the above parameters provide results,

which can be used to establish the feasibility of using VE dampers in seismic

mitigation.

1.6. Layout of thesis

The material contained in this thesis is presented as seven chapters. They are as

follows:

Chapter 1 Introduction

This chapter presents the background and introduction to the

research theme, points out the research problem, describes the aims

and objectives and summarizes the method of investigation used in

this research project

Chapter 2 Literature Review

This chapter reviews the previous literature published on the

behaviour of building facades and passive energy dissipation devices

used in building structures under seismic loading. It then highlights

the necessity and scope of the current research.

Chapter 3 Model Development and Feasibility Study

This chapter details the development of computer model and

feasibility study of building facade system. It presents the calibration

of models and evaluation of results. It then present the results of

finite element analyses of 3 storey building facade systems with and

without VE damping connections obtained under three earthquake

excitations. The main findings of this chapter are then summarised.

Chapter 4

Results – 6 Storey Structures

This chapter demonstrates the results of finite element analyses of 6

storey building facade systems with and without VE damping


9

connections, considering 2 load cases obtained under three

earthquake excitations. Evaluated results and findings are also

presented.

Chapter 5

Results – 12-Storey Structures

This chapter discusses the results of finite element analyses of 12

storey building facade system with and without VE damping

connections obtained under three earthquake excitations. Evaluated

results and findings are also presented.

Chapter 6

Results – 18-Storey Structures

This chapter discuss the results of finite element analyses of 18

storey building facade systems with and without VE damping

connections obtained under three earthquake excitations. Evaluated

results and findings are also presented.

Chapter 7

Conclusions and Recommendations

This chapter highlights the major results and the main contributions

of this research. It makes some recommendations for further

research.


10


11

Chapter 2

Literature Review


12

2. Literature Review

2.1. Introduction

Facade (also known as cladding) is a fundamental architectural term that has existed

for thousands of years. Commonly its principal function has always been for

sustaining artistic purposes which explains their great range of patterns and

materials, as well as colours. The most popular materials for facades are glass, metal

and precast concrete. More significantly, facade also provides shielding against

environmental factors such as wind or rain, as well as providing light, and ventilation

to the structure which are functional needs in today’s structure.

A rapid change to the improvement and advancement of building techniques was

started in the 19th century when the industrial revolution happened. One of the most

important changes was the use of industrialised components in facades. The

improvement and advancement were not only applied to the method of production,

size of individual facade, strength and durability of facade components but also the

structural type of frames holding the facades. As the methods of analysing structures

have been improved, the roles of facades become more significant to be considered

into structural design. In modern designs, in particular with strong frames such as

reinforced concrete or steel frames, facades in wall openings have increasingly

become an integrated system in the whole structure. (G. James Glass & Aluminium

Pty. Ltd, 2003). Both precast concrete and aluminium windows were already widely

used by the early 1930’s. During the Second World War, the moderately rapid

development of new facade systems in large buildings came to a temporary halt.

After the war in 1948, the development restarted and the greatly expanded and

production of building materials opened up a new view of the facade. Construction

of facade progressively increased and reached an extraordinary “boom” during the

mid and late fifties and continued throughout the sixties.

In Australia, because of slow industrial development the appearance of the facade

system was noticeably slower. Window frames were made mainly of timber, while

steel and bronze windows emerged in large commercial buildings and factories after

the war. In the late forties during the rapid building development, light metal and


13

glass facades became popular. (G. James Glass & Aluminium Pty. Ltd, 2003). Figure

2.1 shows the Modern buildings provided with facade system.

Figure 2.1 Modern buildings provided with facade system (http:// nedkahn.com/wind.html)

It is important to be aware that in earthquake events, some items which are normally

non-structural become structurally very responsive. These items will interfere with

the free deformations of the structure during an earthquake. The principle elements

such as facade, perimeter infill walls, and internal partitions are the main concern in

buildings (Dowrick, 1977) .Where these elements are made of very flexible

materials, they will not affect the structure significantly. However for non-structural

reasons they will be required to be constructed of materials such as precast concrete

or blocks or bricks, which would have a considerable effect on the behaviour and

safety of the structure. Although these elements are able to carry little vertical load,

they can act as shear walls in an earthquake with the following important effects.

They are:

i. Reduce the natural period of vibration of the structure, hence changing the

intake of seismic energy and changing the seismic response of the ‘official’

structure

ii. Redistribute the lateral stiffness of the structure, hence changing the stress

distribution

iii. Cause premature failure usually in shear or by pounding

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14

iv. Suffer excessive damage themselves, due to shear forces or pounding

The above effects depend on the flexibility of the basic structure. In the case of very

flexible structure the above effects will be worse. They will be particularly dangerous

when the distribution of such ‘non-structural’ elements is asymmetric or not on the

same on successive floors. (Dowrick, 1977)

During the last decades there has been a substantial increase in interest in facades

and related strength and stiffness due to primary lateral load. In the event of an

earthquake the structural characteristics of facades play a major role that is

commonly overlooked. Facades must also be able to transmit wind forces and their

own weight to the main structure and must be capable of providing a first line of

defence against environmental loadings such as humidity or temperature changes

(Stockbridge 1984).

The facade is a progressively expensive portion of a building which amounts up to

20% of the total building costs. (Facades1980). In arguing the financial value of

facades as well as the costs incurred as a result of facade failures, special attention

must be paid to the issue of protecting them from damage or collapse.

Precast concrete panels are used widely on modern buildings. However, these panels

are very heavy and necessitate specially detailed connections to support the vertical

loads. To resist lateral out-of-plane stress loads, the panel must also be provided with

adequate anchorage. The connections must also be designed to accommodate

thermal, wind and seismic in-plane stress lateral movements of the structural

elements to which they are attached and must also take into account the storey drift

criteria, (Applied Technology Council, ATC, 1998).

In an earthquake event, facades and veneer elements are susceptible when certain

conditions are present. These conditions include:

i. Joints in the facade may not be large enough to allow for in-plane stress drift.

In-plane stress movements can cause cracking of the veneer material, failure

of attachments, or both


15

ii. Anchorage or adhesion of the elements may be inadequately designed

because the original standard attachments may not have been designed for

earthquake forces

iii. Because these elements are located on the exterior, exposure to water can

deteriorate any concealed attachments, which are not easily detected

In many countries it is necessary to consider the effects of earthquakes when

designing and constructing buildings. Earthquakes occur frequently but most are of

insignificant magnitude. The larger earthquakes are less frequent, but are extremely

damaging.

For the designing and constructing of buildings, the effects of earthquakes in many

countries are essential to be considered. Building structures are typically designed to

resist earthquakes as appropriate but the same attention is not always given to the

design of facade. (The Centre for Window and Cladding Technology “University of

Bath” CWCT, 2002). This literature describes the behaviour of buildings during

earthquakes, the effect on facade and the risks associated with facades failure.

Seismic design of building structures in most countries affected by earthquakes,

follow building standards or codes of these countries. However, the type of

earthquake and risk of incidence differ. Therefore the code for many regional or city

buildings comprise specific earthquake requirements. For small buildings with

simple geometry and standard construction, the codes are applied as simple

calculations. This leads to pseudo-static design methods. In this method equivalent

horizontal forces are applied to the structure at each storey as static loads. The code

will limit the permissible building structural movements, which are normally stated

as allowable relative floor movements for any storey (CWCT, 2002). The effect of

the earthquake depends on the form of the building and its geographical location as

well as the site ground conditions. In pseudo-static calculations this is handled by

factoring the horizontal loads. For more complex building geometries, difficult

ground conditions or buildings that have post disaster function (hospitals, utilities,

etc.) it is required to undertake a full dynamic analysis.

For building designs to resist earthquakes there are two possible strategies:


16

i. Flexible construction

ii. Semi-rigid construction

In the flexible construction strategy, the structure is made comparatively flexible, so

that the structure attracts lower loads but experiences larger relative internal

movements. The ground is then able to move during the earthquake while the mass

of the building remains more or less static. Semi-rigid designs are made stiff so that

little relative internal displacement occurs. The mass of the building then has to

move with the ground and larger forces are generated within the structural frame

(CWCT, 2002).

Damage to facade is a common incidence in an earthquake and is considered to be an

important portion of the economic loss. Considerable facade damage has been

reported from the 1964 Anchorage, 1971 San Fernando, 1978 Miyagiken - Oki, 1987

Whittier Narrows and the 1995 Hyogoken - Nambu earthquakes. For earthquake

engineers, the significance of the economic loss of facades damage began to emerge

as a larger field of interest after the 1970’s. (Seike and Sakamoto, 1997) reported on

the damage to precast concrete facade during the 1995 Hyogoken- Nambu

earthquake.

2.2. Facades and facade connections

Prestressed Concrete Institute (PCI 1988, 1989, and 1992) presents some information

on facades, concerning architectural precast concrete facade panels. National

Institute of Standards and Technology, Gaithersburg Facade Research Institute

(NIST GCR 95-681). Some of the basic definitions to be used in this research on

facades are explained as follows:

Facade: A wall unit that resists only wind or seismic loads and its own weight, but

not the gravity loads from the structural framing. It is considered to be a non-load

bearing panel.

Non-load bearing: A term, which is used to indicate that facade panels do not

support gravity, loads from the building’s framing. This term can be used with

architectural or structural precast concrete facade panels.


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Connections: Structures that transfer forces from one facade to another or one

facade to another type of structural member are considered to be a structural

assembly component or connections.

Tie-back (lateral) connections: These are proposed to resist wind and seismic loads

perpendicular to the panel and to keep the precast concrete panel in plumb or in

another desired position.

Bearing (direct and eccentric) connections: Direct bearing connections are

predominantly used for panels resting on foundations or rigid supports where

movements are negligible and are intended to transfer vertical loads to the supporting

structure or foundation. Eccentric bearing connections are usually used for panels

above the first support level when movement of the support system is possible.

The use of non-load bearing precast concrete facade has been the most common

application of architectural precast concrete. They resist and transfer negligible load

from other elements of the structure. In general, they are typically used only to

enclose space, and are designed to resist wind, seismic forces generated from their

self weight, and forces required to transfer the weight of the panel to the support.

(PCI 1989). During an earthquake, building frames suffer large inter-storey drifts,

causing racking of the building facade systems. The facade systems may not be able

to take up such large deformations and this can result in either the functional or total

failure at the connections or damage by pounding (impact) with adjacent facade

panels.

2.3. Earthquakes in Australia

Most Australians do not consider the fact that they live in an earthquake prone area.

But the reality is that Australia lives under the constant threat of earthquakes with

magnitudes that have the potential to injure people and damage property. Although

the overall level of seismic activity is low compared to other countries, Australia still

feels on average, an earthquake of magnitude six or greater every five years and a

two to four of magnitude five earthquakes every 12 months. Australian Earthquake

Engineering Society (AEES) Newsletter, 2003.


18

There have been damaging earthquakes in Australia's recent past. In 1989, a

magnitude 5.6 earthquake killed 13 people in Newcastle and caused around $1.5

billion damage. In 1988 three earthquakes, all with a magnitude greater than Richter

scale 6.0 shook the town of Tennant Creek and cut the gas pipeline running to

Darwin. In 1968 an earthquake of magnitude 6.8 occurred in Meckering, Western

Australia and caused extensive damage to the town. The largest earthquake to have

occurred on the Australian continent in recorded history was located near Meeberrie,

Western Australia in 1941 and had a magnitude of 7.0 on Richter scale. Australia

experiences earthquakes because it is sitting on a huge plate of the earth's crust,

which is moving very slowly northwards at around 7 cm a year. The movement of

the plate causes stresses to build up in the rocks. Occasionally the rocks fracture

because of the stress along lines known as faults, (AEES Newsletter, 2003). An

earthquake is the vibration in the earth released when these fractures take place. The

Australian plate has been subjected to enough stress for mountain ranges to have

formed and the present stresses are sufficient for earthquakes to occur. Figure 2.2

shows earthquake damage in Newcastle in 1989.

When compared to plate margin regions such as California or Japan, the rate of

earthquakes is lower, but relative to other intra-plate regions, Australia's earthquake

activity is moderate to high. The level of the earthquake hazard of Australia's the

most active regions are roughly comparable to that of well known seismic zones in

central USA. This is around 5 to 10 times lower than in California as measured in

engineering terms. The largest earthquake that can occur in Australia is not yet

known but is expected to be above a Magnitude of 7, on Richter scale, similar to

large Californian earthquakes (AEES Newsletter, 2003).


19

Figure 2.2 Extensive earthquake damages in Newcastle (Based on AEES, 2003)

2.4. Design methods

One of the most important and difficult areas of structural engineering is the design

of structures to resist earthquake loadings. When an earthquake strikes, there are

always severe consequences, especially in a highly populated area. The unpredictable

nature and severity of the earthquake itself makes the situation even more crucial.

Earthquake loadings, which are unique, produce greater stresses and deflections

compared to all other loadings. There is always a chance that the earthquakes could

occur once in the life of a structure.

Earthquake loads can be defined as (normally) lateral live loads and can also be

vertical loads. These loads are very complex, vague, and potentially more destructive

than wind loads. In an earthquake zone, every structure must be capable of surviving

all loadings of dissimilar intensities.

Several designs that mitigate the response of a structure due to an earthquake have

been proposed by engineers. Previously the main focus of design was on saving of

lives safety with little or no concentration on damage control. Today’s designs

emphasise limiting the structural damage caused by an earthquake so that the

structure may continue to be used.

Most of the design codes allow four methods of analyses which are Quasi-static

method, Time history analysis, Response spectrum analysis and Static pushover

analysis: (Wilkinson, 1997).

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i. The Quasi-static method assumes that the structure responds in its

fundamental mode of vibration. At its maximum deflection all points on the

structure are at zero velocity such that the static forces in the structure are

equal to mass times acceleration. In linear static procedures, static lateral

forces are applied to the structure to obtain design displacement and forces

(FEMA 273/274).

ii. Time history analysis offers are the best method for design in order to

understand the response of a structural system during an earthquake. It

involves dynamic computer analysis of the structure under the earthquake

loading. A dynamic analysis of a structure by the time history method

involves calculating the response of a structure at each increment of time

when the base is subjected to a specific ground motion time history. The

analysis shall be based on well-established principles of mechanics using

ground motion records.

This method has the advantage over the linear elastic response spectrum

method in that it may be used to analyse the response of highly non-linear

structures. It has the disadvantage that it generally requires more computing

effort and memory and most designers are usually only interested in the

maximum structural response, not necessarily the response at each time

increment,. The ground-motion time histories used should be appropriate for

the specific site and have response spectra, which approximate the

appropriate design spectrum.

iii. Response spectrum analysis, which is essentially a linear analysis, relies on a

carefully conceived structural system, which is capable of non linear

behaviour at extreme levels of excitation. In general, a dynamic analysis of a

structure by the response spectrum method shall use the peak response of all

modes having a significant contribution to the total structural response. Peak

modal responses shall be calculated using the ordinates of the appropriate

response spectrum curve which respond to the modal periods. The Maximum

modal contributions should be combined. A sufficient number of modes

should be included in the calculation of the response so that for each principal

horizontal direction at least 90% of the structure’s gravity load has been


21

accounted for. The peak member forces displacements, horizontal earthquake

shear forces and base reactions for each mode should be combined by a

recognized method. When modal periods are closely spaced, modal

interaction effects shall be considered. Directional effects for horizontal

ground motion shall conform to the requirements. The analysis shall take

account of torsional effects. Where three-dimensional models are used for

analysis, the effects of accidental torsional should be accounted for, either by

appropriate adjustments in the model, such as adjustment of mass locations,

or by equivalent static procedure. Australian Standard (1170.4-1993)

iv. Static pushover analysis is mainly used for investigating the sequence of

formation of plastic hinges. The nonlinear behaviour occurs in discrete user-

defined hinges. The hinges can be introduced into frame elements only and

assigned at any location along the frame element.

A pushover analysis can consist of more than one pushover load case. Each pushover

load case can have a different distribution of load on the structure. For example, a

typical pushover analysis might consist of three pushover load cases. The first would

apply gravity load to the structure, the second would apply one distribution of lateral

load over the height of the structure, and the third would apply another distribution of

lateral load over the height of the structure. There are four different methods of

describing the distribution of load on the structure for a pushover load case:

i. A uniform acceleration can be automatically applied. In that case, the lateral

force automatically applied at each node is proportional to the mass tributary

to that node.

ii. A lateral force that is proportional to the product of a specified mode shape

times its circular frequency squared (ω2) times the mass tributary to a node

can be automatically applied at each node. The user may specify the mode

shape to be used in that instance.

iii. An arbitrary static load pattern may be defined.

iv. Any of the methods described in 1, 2 and 3 can be combined.


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2.5. Current code requirements

The 1979 Australian code, Australian standard 2121 for the design of earthquake

resistant buildings, is published by the Standards Association of Australia. The code

requests that the non-structural elements that are attached to or enclose the exterior of

a building should be capable of accommodating movements of the structure which

results from the horizontal earthquake forces. And they are as follows:

i. All connections and panel joints should allow for a relative movement

between storeys equal to (3.0/K) time the storey drift calculated from the

horizontal forces prescribed by this standard, or 6mm, whichever is greater.

The minimum permissible value of the horizontal force factor K is given for

specific structural systems.

ii. Connections to permit movement in the plane stress of the panel should

include properly designed sliding connections using slotted or oversize holes,

or connections, which permit movement, or other suitable connections which

have been proved to be adequate. The minimum permissible value of the

horizontal force factor k is given for specific structural systems.

iii. Connections should have sufficient ductility and rotation capacity to preclude

brittle failure at or near welds or fracture of the concrete. Inserts in concrete

shall be attached to or hooked around reinforcing steel, or otherwise

terminated so as to transfer forces effectively to the reinforcing steel.

The Uniform Building Code (UBC, 1994) and the Structural Engineer Association of

California (SEAOC “Blue Book” 1990) indicate the following requirement and

recommendations (National Institute of Standards and Technology,

NIST, (GCR 95-681).

Exterior non-bearing, non shear wall panels or elements which are attached to or

enclose the exterior should be designed to resist forces, Fp, and should accommodate

movements of the structure resulting from lateral forces or temperature changes.

Such elements should be supported by means of cast-in-place concrete or by

mechanical connections and fasteners in accordance with the following provisions:

Fp is the seismic force applied to a component of a building or equipment at its

centre of gravity.


23

i. “Connections and panel joints should allow for a relative movement between

storeys of not less than two times story drift caused by wind, (3/8)Rw times

the calculated elastic storey drift caused by design seismic forces, of ½ inch

(13 mm), whichever is greater. Rw is the over strength and ductility factor

that is associated with the lateral load-resisting system. The value of Rw is 12

for steel and reinforced concrete special moment –resisting frames.

ii. “Connections to permit movement in the plane stress of the panel for storey

drift should be sliding connections using slotted or oversize holes,

connections which permit movement by bending of steel, or other

connections providing equivalent sliding and ductility capacity.

iii. “Bodies of connections should have sufficient ductility and rotation capacity

so as to preclude fracture of the concrete or brittle facture at or near welds.

iv. “The body of the connection should be designed for 1 1/3 times the force

determined for Fp.

v. “All fasteners in the connecting system such as bolts, inserts, welds and

dowels should be designed for 4 times the forces determined for Fp.

vi. “Fasteners embedded in concrete should be attached to, or hooked around,

reinforcing steel or otherwise terminated so as to effectively transfer forces to

the reinforcing steel.

The Uniform Building Code (UBC, 1994) contains requirements for storey drift

limitation. The storey drift is defined as the displacement of one level relative to the

level above or below due to lateral design forces. Calculated drift shall include

translational and torsional deflections. The calculated storey drift should not rise

above 0.04/Rw (where Rw is the numerical coefficient representing basic structural

system) or 0.005 times the storey height h for structures having a fundamental period

T of less than 0.7 s. For structures having a fundamental period T of 0.7s or greater,

the calculated storey drift should not surpass 0.03/Rw or 0.004 times the storey

height h. (Cohen, 1995).


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2.6. Performance Based Earthquake Engineering

Performance Based Earthquake Engineering (PBEE) has emerged as a

comprehensive procedure that treats the sitting, designing, constructing and

maintaining buildings in a way that they are competent of producing expected

performance under the earthquakes excitations. The performance of these buildings

should address various requirements of the owners, users and society and will be

measured in terms of the amount of damage sustained by a building under an

earthquake and the effect this will have on the post earthquake use of the building.

Performance based design concept involves multiple target performance (or damage

levels) which are expected to be achieved, or at least not exceeded, when the

building is subjected to an earthquake of a specified intensity.

PBEE is based on the supposition that structural behaviour can be predicted and

assessed with confidence so that the engineer and the client can make intelligent and

informed decisions based on life cycle considerations rather than the construction

costs alone. PBEE will necessitate a shift from empirical methods of design and

evaluation of structures to predictions based on their performance under realistic life

time loadings. Such an approach is feasible in view of improved knowledge on

earthquake loadings and structural response. PBEE methods will enable innovations

for enhancing performance in comparison to the rigid code based methods. The

concept is not limited to buildings alone, but applicable to all structures. (Krawinkler,

1999; Hamburger, 1997).

2.7. Basic components of facade connection systems

The facade panel has many different kinds of connection systems, but in general they

are all composed of the following three components:

i. Panel fasteners, which normally comprise an insert, built into the precast

panel to provide the panel anchorage.

ii. Structural fasteners, which anchor into the building structure and is a second

insert embedded in the concrete structure, typically with bolts, bearing plates,

angles plus bolts.


25

iii. Connector body, is typically a steel angle that forms the body of the structural

connection between the facade panel and the main structure and can be

constructed from partially or continuously threaded bars, gusset plated angles,

or tee sections, slotted or non-slotted angles.

Figure 2.3 Typical facade connection components (Earthquake Engineering and Structural Dynamics, Pinelli at al., 1996)

2.8. Common or conventional facade connection systems

For the serviceability drift limit the framing should remain basically elastic.

Currently, the maximum allowable storey drift is considered to be 0.005 of the storey

height, based on low pseudo-static design forces. For instance if 3657 mm storey

height is assumed then, this gives a storey drift of 0.005x12x3657.6 = 219.456mm.

NIST, (GCR 95-68). The UBC further requires that the panel should be provided

with two types of connectors.

i. The connector for gravity loads that are free to slide sideways to

accommodate drift movement.

ii. The connector should resist smaller horizontal forces and be flexible in the

opposite direction and will deflect to accommodate movement.

Hegle (1989) provided an explanation on design considerations to supply an

economical attachment to precast concrete facades in building structures. He stated

that the architectural precast concrete facade connections are usually designed for

transmitting the facade’s load to the structure exclusive of any effect on the response

of the structure to vertical loads and lateral wind or seismic loads. Floor and roof

members must be able to deflect and column drift must be accommodated with no

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enforcing loads on the facade connections to the structure. He also presented

information on facade panel configuration, panel connection design, and connection

types and loads. He stated that for facade panel configuration,

i. The architectural design of a precast building facade is typically improved by

the use of real and false joints to create a pattern. It is very important to

carefully choose the location of real joints between the individual facade

panels.

ii. The joint will create three types of panels namely; 1) storey height wall

panels, 2) horizontal spandrel panels and 3) vertical column cover type

panels. First, in order to follow the building drift under lateral loading, the

joints must allow the individual panels to move as required. Each storey

should be provided with at least one real horizontal joint continuous around

the building. This will allow the panels that are attached to one floor to move

with that floor’s drift relative to the panels above and below them which must

move with their floor’s drift.

iii. The location, size and capacity of the building structure must be considered in

order to support the loads from the facade panel connections. The panel

bearing connections should be placed at the building columns as they are

more economical and will provide stiffer resistance to the panel eccentric

loads. It is relatively important that the overall size and weight of each

individual panel be limited by the capacity of the local production facility,

truck transportation legal limits, truck and crane access around the structure,

as well as the available crane capacity.

It was stated that the connections of the facade panel must be able to transfer gravity

load as well as wind and seismic loads from the panels to the structure. NIST, (GCR

95-68). Each panel is allowed to have only one or two bearing connections and not

more than two. The use of more than two bearing points to support a panel will

create unknown loads in each connection, as the panels are usually very stiff

compared to the supporting structure. The bearing connections are generally placed

near the ends of the panels in order to provide a stable base during panel erection and

are designed to transfer panel gravity loads, wind and seismic loads perpendicular to


27

the panel. There is also the possibility that they transfer seismic loads parallel to the

panel. The lateral load connections are only transferring the loads that are

perpendicular to the panel. They are mainly designed in order to allow the structure

to move vertically and horizontally parallel to the panel while under perpendicular

loading. NIST, (GCR 95-68). The configuration and design of each type of panel

connection must take into consideration a number of important characteristics. In

order to make the building facade system safe and economical, connections must be

designed for the following.

i. To transfer erection as well as final loads to the structure.

ii. For ease of fabrication.

iii. To accommodate building construction tolerances.

iv. For economical panel erection.

v. To permit the structure to move: the connections must be capable of carrying

their design loads while the structure is deflecting due to the gravity or lateral

loading. This may be accomplished with slotted holes or bending of steel

connection members.

vi. To fit within the architectural finish.

Facade panels were considered non-load bearing components until relatively recently

by designers. In other words, facade panels were not designed to contribute to the

gravity and lateral load resistances of the structure. Facade design has often provided

similar guidelines to that provided by the Design Codes of America and the Precast

Concrete Institute (PCI). These design manuals have the following recommendations

and requirements:

i. In order to permit a more accurate determination of forces, a system of

connections should be statically determined.

ii. There should be a reduction in the internal stresses.

iii. In order to accommodate storey drift and volume change, the panel should be

allowed to move in its plane stress.


28

iv. During an earthquake contact should be prevented between the structural

frames. Torsional moments on supporting beams should also be minimised.

v. There must be movements at the connections by either the ductile bending of

steel connections or sliding within the slotted holes.

vi. The anchors (eg bolts and inserts) or welds that attach the connectors to the

concrete panels or the structure are designed for four times the force on the

panels.

Structural engineers frequently overlook the importance of facade and facade

connection design because of the misconception that the facade is a non-structural

component. As a result, engineers repeatedly leave the choice of facade and its

connections entirely to architects and contractors, (Spronken, 1989). Facade panels

are normally provided with four connections, two at the top of the panel, and the

other two connections at the bottom of the panel. The connections are responsible for

keeping the panel attached to the structural frame of the building by supporting the

dead weight which is normally generated by the panel. In general, the conventional

connections are divided into two categories due to their load carrying function either

bearing or non-bearing connections. The connections located at the bottom of the

panel are rigid connectors and are responsible for providing resistance to gravity and

lateral loads such as wind. These connections are called load bearing connections.

Figure 2.4 illustrates such a load bearing connection.

Figure 2.4 Load bearing connection (Based on Precast Concrete Pty Ltd Australia, 2003)

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The connections located at the top of the panel are non load bearing connections and

are commonly known as tie-back connections. The tie-back connector acquired its

name from its fundamental function of simply keeping the facade panel in the correct

plane stress. NIST, (GCR98-758) Figure 2.5 shows conventional facade connections.

Figure 2.5 Typical configuration of facade system (Based on Goodno et al., 1998)

The tie-back connection is designed to deform under lateral forces and thus does not

transmit racking forces to the panel. Furthermore the tie-back must have the

capability of accommodating the out-of-plane stress forces on the panel, containing

wind (Rihal, 1988). Indeed, the increasing number of failures in facades during

recent years caused an awareness and concern among engineers regarding facades

and methods for passive and active control to satisfy the dynamic response of

buildings. A great deal of attention is now given to facades and their connection

designs. As a result, several studies have revealed that conventional facade

connection, which totally disregards the panels ability to carry any lateral load or add

lateral stiffness, are not justified. In fact the research results have proved that facade

systems affect the structural stiffness noticeably and hence the dynamic response of

buildings, in contrast to the traditional beliefs that the facade is a non-load bearing or

non-structural element. Facade connections play a critical role in the interaction

process as facades induce interaction with the supporting moment-resisting frame as

well as restraining the racking deformation of the frame. As a consequence it

significantly stiffens it against lateral loading. Instead of reducing structural panel

interactions in an earthquake condition, there is a possibility to take advantage of it to

dissipate energy, thus decreasing the response of the structure.

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2.9. Advanced facade connections

To improve facade performance under seismic loads, some researches developed

what are called “advanced connections’’. The main idea for the design of advanced

connections is to reassign a structural role to the architectural facade in order to

introduce the added passive damping into the structural system. The traditional

method of facade design involves an attempt to try to isolate the facade through,

various designs of connections, however the advanced facade connections barely

attempt to integrate the facade system into the structural frame of the building. The

designing of an advance facade connection is a complex process and will be time

consuming if it is used for a commercial purpose. But it will be justified by the

overall increased efficiency of structural facade functioning in regard to dynamic

response, such as in a seismic situation. The advanced facade connection can provide

a better uniformly distributed energy dissipation over the height of the building

without involving any structural members. This can be the most remarkable benefit

that advanced facade connections have over conventional connections. The above

significant benefit preserves the structural integrity of the building. The use of

appropriate advanced connections for integrating the structural properties of the

facade should provide a reduction in the structural response of the building. In order

to attain this, the design of the advanced connections must be very accurate,

providing both lateral stiffness, ductility and also the ability to dissipate energy,

during an earthquake. Consequently, an advanced connection can demonstrate

greater properties of ductility and damping, which result in high-energy dissipation

with no failure throughout either moderate or strong earthquakes. In order to protect

the facade panels, the connections are also responsible for limiting the forces

transmitted into the panel.

2.10. Design criteria of advanced facade connections

The advanced connection must address practical issues such as manufacturability and

cost in addition to its ability to satisfy all structural requirements. The feasibility of

the advanced facade connection concept must consider the issues of practicality and

economics. The issues include sustaining wind and gravity loads, durability,

fabrication and installation as well as being simple, replaceable and cost effective.

Moreover, the structural expectations should be achieved through advanced


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connection design and should be capable of limiting forces transmitted into facade

panels. It should also ensure that inelastic responses will be mostly concentrated in

the facade system, thereby sparing the structure from extensive damage.

Finally, it is also important for the facade connection to be designed in such a way

that it will fail at a ductile weak link where it could bend beyond the elastic limits.

The connection can not fail in a fragile and disastrous manner. For an advanced

facade connection system, a number of passive procedures are discussed and they are

as detailed in the following sections:

2.10.1. Friction mechanism

A friction mechanism is the basis for a number of proposed connection designs

(Tyler 1977, Pall 1980 and Palsson 1982b). A potential candidate for friction damped

facade connection is the slotted bolted connection developed by (Grigorian, et al.

1987). One of the predominant benefits of the friction mechanism is its capability to

dissipate a huge amount of energy through friction because of its inelastic

functioning which is very well explained by a large rectangular hysteretic loop, while

exhibiting negligible fade over several cycles of reversal. The friction mechanism

also has some defects. Obviously this type of design experiences corrosion, and that

is a critical factor for friction mechanisms. In addition, as in conventional tie-back

connections, an insufficient length of the slot could reduce the effectiveness of the

friction mechanism. In general, friction mechanisms exhibit a wide range of

extremely desirable properties, and should be further explored through

supplementary experiments.

2.10.2. Composite material mechanism

The utilisation of a composite system which offers significant benefits can be another

choice for the design of an advanced facade connection. This involves a connection

manufactured from different types of materials, chosen for varying properties,

including ductility and strength. NIST, (GCR 95-681). A flexible connection made

from steel-rubber composite is a good example of this mechanism. Figure 2.6

illustrates a steel-rubber composite.


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Figure 2.6 Steel-Rubber composite (Based on Kemeny and Lorant, 1989)

The use of energy dissipating composite facade connections remains a relatively

unexplored system compared to other energy dissipation mechanisms, despite it

being well viewed in the past. It is important to say that the major requirement of an

excellent facade connection is one that is simple in design. Indeed, designs based on

the composite system have frequently led to enormous complexities. Therefore,

researchers have often tried to disregard the mechanism. NIST, (GCR 95-681).

However, based on this system some promising designs have been produced which

include ductile inserts (figure 2.7a), the ductile loop (figure 2.7b), double taper

flexure (figure 2.7c), and the single taper flexure (figure 2.7d).

Figure 2.7 Composite façade connection (Based on NIST GCR 98-758, 1998)

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2.10.3. Torsional mechanism

The torsional devices just like other systems, offer some distinct benefits.

Specifically, due to the relationship between uniform distribution of torsional

moment and the properties of the material, it provides greater energy absorption

qualities. On the other hand, a progressive ductile failure which is distributed over

the entire length of the connection device is also proposed by torsional devices.

NIST, (GCR 95-681). As with other systems, torsion connections have the capability

to reduce premature failures and are considered to have stable behaviour. However,

the concerned difficulty is an issue commonly linked to the design of a purely

torsional device.

Figure 2.8 Conceptual torsion connector (Based on NIST GCR 98-758, 1998)

The conversion of the inter-storey drift into a proportional rotation that is required to

activate the torsion device is very complicated. However, there have been several

appealing conceptual facade connection designs that are based on torsion in the past,

and are exemplified as in Figure 2.8. Generally, research presented up to now

regarding employing torsion as the base of an advanced facade connection design is

quite preliminary. However, the advantages of this system suggest the need for

further research.

2.10.4. Flexural mechanism

For many years the flexural mechanism has been recognized as one of the most

popular systems for advanced facade connection designs. A large number of designs

have been produced using this energy dissipation mechanism. NIST, (GCR 95-681).

In fact, flexural mechanism designs utilize the idea of flexural deformation to the

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connection system which is comparable to the concept of simple beam bending.

Flexure is effortlessly comprehended by all structural engineers as it is a basic

element of structural engineering. The following are two examples of advanced

facade connection designs which contain the flexural mechanism. Figure 2.9 shows

the ductile loop connection.

Figure 2.9 Ductile loop connection (Based on Earthquake Engineering and Structural Dynamics, 1996)

Pinelli et al. (1993a) conducted experimental testing on the behaviour of facade

connections when subjected to combined shear and bending. They continued with an

evaluation of advanced facade connection designs. The main purpose was to

establish and evaluate the characteristics of each of the connectors in terms of

stiffness, ductility and energy dissipation.

Figure 2.10 Advanced tapered facade connection (Based on Pinelli, Goodno, and Hsu 1993)

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The experimental results showed that these tapered designs will provide an almost

rectangular hysteretic loop. As a result of plastification these loops demonstrated

high-energy dissipation. The connector could be placed between a panel and the

supporting structure through a bolted attachment as shown in Figure 2.10.

Towashiraporn et al. (2002) reviewed passive energy dissipation devices for seismic

response modification applications and discussed current design guidelines. They

also discussed three resent applications of metallic hysteretic damping devices and

demonstrate the versatility of passive energy dissipation devices.

2.11. Interaction between structure and facade

It is very important to understand the level of contribution to seismic resistance that

is usually provided by a facade system. During an earthquake the interaction between

facades and the structure occurs and is considered to be one of the most substantial

relationships between them. (Arnold, 1989) outlines four levels of potential

interaction between the structure and the facade system.

i. Detachment: It could be anticipated that the facade gets completely detached

from the structure and will not strengthen or stiffen the building; it is

frequently based upon the use of a push-pull type connection. As complete

detachment is probably impossible, the facade does behave independently

from the structure.

ii. Accidental Participation: The facade actually plays a significant role in

strengthening or stiffening the structure, even though it is expected to detach.

iii. Controlled Stiffening or Damping: When a facade is designed it is expected

to stiffen or dampen the motion of the structure. This is typically engineered

using special connections that possess damping characteristics.

iv. Full Structural Participation: It is expected that the facade should fully

participate in the load carrying capability of the structure.


36

2.12. Viscoelastic dampers

Viscoelastic dampers consist of plates separated by inert polymer materials and

dissipate energy by shear deformation of the copolymer. Like all dampers, VE

dampers are temperature sensitive, which could create special challenges for external

fittings on structures. They are mostly used in structures where the damper undergoes

shear deformations. Force-displacement characteristics of VE dampers are influenced

by the function of either the relative velocity between the ends of the damper or the

frequency of motion. However, the response of these devices may also be a function

of relative displacement. In VE devices, stiffness and damping coefficients are

frequency dependant, and the damping force is proportional to velocity. In the early

1990s research and development of VE dampers for seismic application was started

and extensive experimental programs were designed and carried out for steel frames

and reinforced concrete frames. Fig. 2.11 shows Idealized force-displacement loop of

VE devices.

Figure 2.11 Idealized force-displacement loop of VE devices (Based on Soong et al., 1997)

VE dampers were found through experimental (shake table) testing of large-scale

reinforced concrete and steel frames that were fitted with VE material to play a very

significant role in improving the response of the frame which includes reduction in

the inter-storey drifts. This was confirmed by Min et al. (2004), Chung et al. (1995)

and Foutch et al. (1993).

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Figure 2.12 Typical VE solid damper (Based on ASCE, 1997)

The VE dampers developed by Showa and Shimizu corporations have confirmed a

50% reduction in the seismic response of the frame equipped with VE dampers.

Similarly, the VE shear damper (Super-plastic silicone rubber) developed by

Kumagai-Gumi Corporation has confirmed a reduction of up to 60% through a ½

scale 3-storey steel frame test. Fig.2.12 show typical VE solid damper.

An experimental test of direct shear seismic dampers and steel plate devices was

undertaken by Bergman and Hanson, (1988). The direct shear seismic dampers

utilize VE material in shear, and steel plate devices depend upon the yielding of their

steel plate elements for energy absorption. The results confirmed that all dampers

dissipated a sufficient amount of energy that caused a considerable amount of

damping in building frames. However some VE dampers may be dependent on shear

strain level, previous shear distortion and excitation frequency. It has been also found

that the damping and stiffness degradation of the steel plate devices are independent

of displacement amplitude. Moreover, the hysteretic behaviour of these devices is

untouched by the earlier cyclic distortion, and the fatigue resistance is likely to be

sufficient even during extreme earthquake situation.

Mahmoodi (1969) and Mahmoodi et al. (1989) carried out analytical studies on the

seismic performance of the same discrete VE dampers. The dampers were positioned

on the main diagonals of a ten storey steel frame structure. Sandwiched between a

centre plate and two flanges, the VE material deformed in pure shear, providing

energy dissipation in proportion to its volume. Damper stiffness values were

calculated based on damper dimensions and modal damping estimates were made

based on the cyclic shear deformation of the VE material using a relationship

between strain and absorbed energy. Frame response with the dampers was at least

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50% less at each floor level than the response of the bare frame when subject to

earthquake excitations. The behaviour aspects of the building facade systems have

been investigated by some researchers with varying objectives; some of them are

presented in the following chapter.

2.13. Research on seismic effects on facade

Weidlinger (1973) promoted the idea of using the facade as an integral part of the

wind bracing system. He observed that facades can be incorporated into structural

resistance system to increase the lateral stiffness of high-rise buildings; He also

studied the behaviour of shear panels. (Gjelsvik, 1973) reported on the interaction

between frames and precast panels. He focused on the effect of facade on the lateral

strength capacity of a frame with simple beam-column connections.

Kallros (1987) studied the behaviour of connections in thin precast concrete panels

under earthquake loading using experimental testing. He tested a number of

specimens to observe their behaviour under cyclic loading and found a failure in the

inelastic range. This failure was considered to be either because of spalling of the

concrete that would result in large deflections or due to rebar failure, which would

result in small deflections. It was also found that the yield stress of the rebars had an

influence on the fatigue rather than the strength of the connection. In addition, he

observed that the connections tied to embedded rebars showed better behaviour

compared to the connections tied to a wire mesh.

Oppenheim (1973) studied the effect of facade on the dynamic properties of a steel

building frame. It was concluded that in balanced designs (where panels are of

stiffness comparable to the frame) the upper storey panels will require large

deformation capacities because of the whipping effect. Goodno et al. (1983)

investigated the seismic response of facade buildings. It was noted that the addition

of facade stiffness changes the dynamic properties of the structure and causes it to be

less or more sensitive depending on the selected ground motion. As a result, it might

not always be conservative to neglect the lateral stiffness of facade during the design

process.

McCue et al. (1975, 1978) studied the effect of the facade stiffness put into a

structural frame in an earthquake situation and found that the stiffening effect of the


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facade could result in a shift of vibration frequencies of the building toward a more

critical earthquake ground motion frequency range. This could result in higher

seismic response.

Sack et al. (1981, 1989) conducted an experimental testing on a one-bay steel frame

that was subjected to in-plane stress dynamic forcing. The frame had two panels that

were made of precast concrete. The panels were connected by two clip angles at the

bottom and two rods at the top to the frame. They found that the rods were

susceptible to low cycle fatigue and the top connectors in horizontal bending were

found to be exceedingly stressed in horizontal bending when they were subjected to a

number of earthquake floor motion records.

Anicic et al. (1980) performed experimental studies on two reinforced concrete

facade panels, in which only cyclic loads perpendicular to the plane stress of the

panels were applied. Throughout the studies no difference in behaviour could be

observed between the panel with an opening and the one without an opening, and it

was shown that the panels withstood much higher loads than computed, failing by

plastic buckling of the main web reinforcement.

Rihal (1988,1989) studied the behaviour of precast concrete facade panel

connections using cyclic in-plane stress racking tests. The panels were fitted at the

top with threaded-rod lateral connections and at the bottom with bearing connections.

Relative motion across the connection elements was measured. He found that with

an increase in the length, the load-capacity of the threaded rod specimens reduced.

Research in the area of usage of facade in combination with the structural system has

been conducted since the 1960’s. Analytical and experimental studies conducted by

Goodno and Craig (1989) have shown that facades can have a major influence on

both the structure beneficial and detrimental behaviour of structure.

Freeman (1989) investigated the behaviour of a building fitted with facade under

earthquake loading. He found that the active participation of facade would cause an

increase in the damping of the structure and a dissipation of energy. He also reported

that with the structural stiffness increased with the period of vibration of the building

which could reduce and result in an increase in the seismic force from typical elastic


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design spectra. According to the static design analysis the additional stiffness will

result in smaller deflections, and in general this reduction in deflection would also be

seen in nonlinear dynamic analyses. However, Spronken (1989) reports the

contractual and legal implications which are required for a facade system to be used

as part of the structural system. He stated that these issues depend upon the

engineer’s responsibility for the detailing and performance of the facade. The

structural engineer is usually provided with a very limited review and design input

into the facade details.

Smith and Gaiotti (1989) studied the analytical interaction of building frames with

facade and without facade. They found that the detailing and construction according

to Precast Concrete Institute PCI did result in interaction occurring between the

facade and frame. The connections they considered were cantilever steel tube

bearing bottom connections and vertically slotted bolted angle top connections.

They showed that the building frame with facade could have racking stiffness as high

as 35 times to the building frame without facade with a resulting reduction in the

elastic deflection from 126 mm to 3.6 mm. This increase was the result of the

forward rotation of the panel due to bending of the beam that resulted in a reversing

moment being applied to the beam. They reported beams were placed in quadruple-

curvature bending deformation.

Charney and Harris (1989) reported that the precast facade sliding connections

should only resist the vertical and out-of-plane stress loads, typically by the use of a

horizontal slot in the steel angle used for the connections.

Pinelli et al. (1992) studied metallic dampers in a 6-storey 3-bay moment-resisting

steel frame building. They provided the test frame with a two precast facade panels

per bay, as shown in Fig. 2.13. The panels were considered to be rigid. Each panel

was attached at its bottom to the steel frame by two rigid bearing connectors and at

its top by two advanced connectors, which were metallic hysteretic dampers. The

computer program DRAIN-2D was used to carry out the analysis. Each bearing

connector was modelled using simple linear elastic spring with a very high stiffness.

The advance connectors were modelled as a nonlinear translational spring element

which could incorporate bilinear behaviour with strain hardening and inelastic


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unloading. A nonlinear dynamic (time-history) analysis was used to design the

facade connector system.

Several different earthquake ground motions with widely different frequency

content, duration, and peak acceleration were used. Results of the comparative

analyses were presented in terms of percentage of input energy dissipated in the main

structural elements and in the facade connectors, the maximum floor displacement,

thus the maximum inter-storey drift. It was reported that the advanced connectors

produced considerable energy dissipation up to 79% of the input energy and the main

structural system was still in the elastic range. They also confirmed that the

maximum displacement in the retrofitted frame was reduced to approximately 52%

of the reference case when the advanced facade connection system was fully

implemented. Fig.2.13 shows the building design model for (a) The DRAIN-2dx 2D

frame model and (b) a typical bay with panels and connections.

Figure 2.13 1/4-Scale Building design model (Based on Pinelli et al., 1992)

The application of the ductile or advanced Passive Energy Dissipation (PED) facade

connectors developed by Pinelli et al. (1992) was further investigated by Goodno et

al. (1998). They studied a 20-storey steel frame fitted with precast concert facade,

using computer analysis to investigate the performance of the building as well as the

validity of the facade connectors. For the bearing connections at the bottom panel

nodes, the connector elements in both horizontal and vertical directions were

assumed to be very stiff and elastic. The connectors at the two top panel nodes were

modelled as non-load-bearing tieback connectors, and each node included a vertical

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and a horizontal connector. The bottom bearing connection was assumed to unload

elastically. The vertical connector stiffness was set to near zero.

Figure 2.14 A 20-storey baseline building, (a) the elevation (b) the plan view (Based on NIST GCR 98-758, 1998)

The horizontal connectors were assumed to represent the advanced facade connectors

and were modelled as bilinear spring elements with inelastic unloading. The

advanced properties of the facade connectors were designed with an energy

dissipation criterion. Computer programme DRAIN-2Dx was used and nonlinear

time history dynamic analysis was carried out to investigate the behaviour and

performance of the baseline building as well as the validity of the advanced

connections. They found that the passive energy dissipation system performed well

and could reduce the response of building structures under dynamic loads.

Pinelli et al. (1989) studied the behaviour of low-cost friction-damped connections in

a 10-storey concrete frame office building, under the earthquake loading. The

architectural precast concrete facade panel were connected at the top with four

friction-damped connections. The bottom of the panel was connected with relatively

stiff traditional load support connections. Comparison of the results was made with

an unclad frame. Computer programme DRAIN-TABS (23), was used and a three

dimensional non-linear time-history dynamic analysis were carried out. They found

that in comparison with results of the unclad frame, the friction-damped connections

were more effective in reducing the overall response of the structure in an earthquake

simulation.

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Cohen et al. (1993) carried out a design study of structural facade panels with energy

dissipating facade to frame connections for a seismic resistant design using non

linear dynamic analysis. They found that the clad frames performed well, based on

observations on maximum inter-storey drift, maximum plastic hinge rotations in the

frames, and maximum ductility demands on the facade to frame connections. It was

also reported that the ductility demands on the facade to frame connections were

modest, and the forces transmitted to the facade panels were reasonable. They finally

concluded that the structural facade could substantially improve building behaviour

for the new design, and could be attractive for a seismic retrofit.

Behr et al. (1995) carried out dynamic racking tests on facade glass elements. The

main idea of their research was to investigate the breakage and fallout behaviour of

various types of architectural glass elements in a dry glazed facade system under in

plane stress and out of plane stress dynamic motions. The result shows that most of

the glass types that were found to be prone to glass fallout during the in-plane stress

tests were significantly broken or subsequently fallout when the out of plane stress

motion was added. They found the unanchored window film to be ineffective in

resisting post-breakage glass fallout under dynamic racking motions. In contrast

6mm annealed laminated glass and heat-strengthened laminated glass showed no

glass fallout during the out-of plane stress tests, similar to that which did not

exhibited fallout during the in-plane stress tests. The results from the out-of-plane

stress test also showed that 10mm heat-strengthened monolithic glass revealed no

fallout, while 9.525mm annealed monolithic glass showed insignificant glass fallout.

Wulfert and Behr (2000) conducted a dynamic racking and air leakage test. The test

was carried out on full-size specimens of a new, earthquake-isolated facade system

as well as a conventional facade system, which was used as an experimental control.

A comparison study between the responses of the Earthquake Isolated Curtain Wall

System (EICWS) to that of a comparable conventional facade system tested under

similar dynamic displacement conditions was carried out. They conducted air

leakage tests in order to identify the serviceability performance of both facade

systems during the dynamic racking tests. The main objective of the research was

that no glass cracking or glass fallout would occur in EICWS during simulated inter-

storey drifts and also no serviceability degradation would occur up to a drift index of


44

2 %, which is representative of inter-storey drift limits for life safety in model

building codes. The EICWS functioning to accomplish inter-storey structural

isolation by employing a continuous “seismic decoupled joint” at every single storey

level, in conjunction with a specialized structural support system to attach the

vertical mullions to the building frame at each storey level (as well as only at that

storey level).

The result showed that the earthquake isolated facade system had outstanding

performance in terms of both serviceability (glass cracking and air leakage) as well

as life safety (glass fallout). They did not observe any glass damage in the earthquake

isolated system during the test. The dynamic racking displacement limit of the test

facility corresponded to a drift index of 4.9%. The conventional system demonstrated

vulnerability which showed massive glass cracking and glass fallout at dynamic

racking drift. The drift was showed to be 1.9% and 3.1 %, respectively. The air

leakage rates through vision panels in the conventional system stayed constant up to

a drift index of 1.9 %, after which the air leakage rates increased rapidly. In contrast,

air leakage rates through vision panels in the earthquake –isolated system remained

unchanged up to the 4.9% drift index capacity of the test facility.

Wulfert and Behr (1998) proposed an “Earthquake-Immune System” to increase the

serviceability and life safety performance of facade systems under earthquake loads.

They confirmed that this system, can be adapted to stick-built, panellized and other

facade frame types, and is fundamentally immune to damage resulting from swaying

motions in the building frame. Figure 2.15 illustrate only the in-plane stress lateral

inter-storey drifts and also emphasizes the fundamental discrepancy between

conventional facade systems and the proposed EICWS.


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Figure 2.15 Schematic representations of fundamental vibration modes

For facade systems to be immune to earthquake-induced damage, the writers

submitted that it must not show any sign of serviceability degradation (i.e., frame

distortion, glass cracking, weather seal damage, increased air or moister infiltration,

etc.) during a moderate earthquake. Also not to show signs of exceeding an ultimate

limit state (i.e., glass fallout) during a severe earthquake.

Schematic depictions in Figure 2.15 contrast the fundamental vibration modes of

typical building frame facade with a conventional facade system to that of the same

building frame facade with an EICWS. In conventional facade systems the vertical

mullions span more than one building storey and are connected to the building frame

at more than one storey level. In the proposed earthquake isolated curtain wall

system the vertical mullions span only one building storey and are attached at the top

of the building frame at only that particular storey level. Consequently, in

conventional facade systems, inter-storey movements in the building frame can cause


46

facade frame distortion and subsequent facade panel damage (architectural glass

panels, aluminium panels, etc.). In contrast, these same inter-storey movements

should cause no damage in proposed EICWS because of the “decoupling” that is

achieved between adjacent storeys in EICWS frames.

Ali M. Memari1 et al. (2004) studied the effect of vertical ground motion on design

of precast concrete facade panels in seismic regions, mainly in near-source areas.

They chose a spandrel-type precast concrete facade panel for detailed study. In this

study, the seismic provisions of the International Building Code 2000 and Uniform

Building Code 1997 were used in order to verify the design forces on the facade

panels, that was originally designed as an example in a PCI publication. The

provisions of the two codes have been compared in terms of their needs in regard to

vertical ground motion considerations and near-source effects. In order to

demonstrate an example of incorporating vertical spectral acceleration effects

directly in load combinations, they have also used the results from the latest research

on the relationship between vertical and horizontal ground acceleration components

as a function of source-to-site distance. More specifically, they addressed the

analysis and design load calculations for a typical spandrel facade panel highlighting

the question of vertical ground acceleration and near-source effects. Design forces

were evaluated for cases with and without near-source effects. They conclude with a

discussion of finite-element modelling and frequency analysis results of the spandrel

and floor-to-floor types of facade panel. From this study they have determined that

vertical ground motion will cause an increase in the design forces for connections of

heavy facade panels, especially in near-source regions, with the magnitude of the

increase dependent on the source-to-site distance.

Bozorgnia et al. (1998) in their recent study have emphasised the importance of

vertical components that need to be paid attention in the analysis and design of non-

structural elements and their connections to structural systems especially in the near

source region and for sensitive non-structural elements. This emphasise was based on

the accessibility to the extensive near-source records, which demonstrate high (as

high as 85% g) vertical acceleration values during the recent earthquakes such as the

1994 Northridge earthquake (EERI,. 1995).


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Figure 2.16 Details of selected spandrel facade type (Based on Bozorgnia et al., 1998)

Studies carried out for example by Bozorgnia and Campbell (2004) have

demonstrated that the vertical-to-horizontal spectral ratio can surpass the 2/3

assumption that is recommended by codes, specifically in near-source areas. All the

structures or components have the fundamental periods, roughly in the range of 0.05

to 0.2s, the ratio of vertical to horizontal response spectra is possibly larger than 2/3,

especially when source-to-site distance becomes smaller. They highlighted the

importance of considering a properly developed vertical design spectra for such

conditions, as the use of the 2/3 factor may not be conservative. Details of the

selected spandrel facade type are shown in Figure 2.16.

With respect to the connections of heavy non-structural facade panels, this study has

confirmed speculation by some researchers that in close to site regions, vertical

ground acceleration can intensify the design forces. For near-source conditions,

vertical ground acceleration spectra should be considered for a more conservative

design according to the calculations following (UBC, 1997) and (IBC, 2000), and use

of recently suggested methods for generation of vertical ground acceleration spectra.

In addition, frequency analysis of a typical spandrel precast concrete facade panel as

well as finite-element modelling have shown that further amplification of vertical

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motion is normally improbable due to the huge values of dominant frequencies.

However, it has been mentioned that some amplification would happen for the type

of storey high facade panels considered in the study. Conversely, high vertical

accelerations that have been associated with high vertical frequency, will lead to

additional forces in the facade connections.

During the past few years the analytical and experimental research studies have

frequently shown that facades always unfavourably influences the behaviour of

building systems. On the other hand, the stiffness, strength, mass and damping

properties of the facade panels and connections remain to be neglected by designers.

In relation to the above issue Cohen (1995) has stated in his paper that a rational

basis must be developed and implemented for engineering of all facade that could

pose life-safety hazards and for designing heavy facade as an integral part of the

structure of three-dimensional building systems.

An experimental test of direct shear seismic dampers and steel plate devices was

undertaken by Bergman and Hanson (1988). The direct shear seismic dampers utilize

VE material in shear, and steel plate devices depend upon the yield of their steel

plate elements for energy absorption. The results confirmed that all dampers

dissipated a sufficient amount of energy that caused a considerable amount of

damping in building frames. However some VE dampers may be dependent on shear

strain level, previous shear distortion and excitation frequency. They also found that

the damping and stiffness degradation of the steel plate devices were independent of

displacement amplitude. Moreover, the hysteretic behaviour of these devices was

untouched by the earlier cyclic distortion, and the fatigue resistance could even be

sufficient during extreme earthquake situations.

2.14. Conclusions to the literature review

2.14.1. Summary of the literature review

Research on facade behaviour, facade – building interaction and connection

behaviour had been isolated and focused in different aspects.

The structural models treated by the different researchers were in general different

from each other with no attempt to develop research models. The existing research


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mostly considered low rise buildings of single construction type which were only

objected to one seismic event. This variability is research modelling resulted in test

data which could not be readily compared.

There is no comprehensive research available on the connection types applicable to

structures for a range of heights under different earthquakes. This project recognises

such a gap in the knowledge and aims to carry out a comprehensive research project

on building facade system. In this research VE dampers were used to model the

energy absorbing connections. The parameters considered are:

i. 4 Structural models (3,6,12 & 18 storey building)

ii. 2 Different load cases

iii. 3 Different earthquake records with different PGAs

iv. Different connections properties (and optimum values)

v. Facade types and influence of mass

This project will generate research information on building facade connections under

seismic load to facilitate optimum performance.

This literature review looked at the tremendous changes in building techniques in

terms of the use of industrialized components in facades. It then provided the basic

definition of facade and facade connections. A brief background of seismic activity

and seismic effect on building structures is then explained. The design of structures

to resist earthquake loadings through the current code requirements is presented next.

It was also important to look at the connection properties and structural detailing of

connections, followed by the basic components of facade connection systems,

common and conventional facade connection systems. Seismic mitigation principles

are discussed next, followed by a description of a number of available passive energy

dissipation devices using a range of material and damping mechanisms that work on

principles such as advanced facade connections, friction mechanism, composite

material mechanism, torsional mechanism and flexural mechanism. Viscoelastic

dampers were also described as part of the review of PED devices. Finally, the levels

of potential interaction between the structure and the facade system and a brief


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explanation about the unexpected interaction between the facade and structure are

also described.

A number of strategies and recommendations the effective use of passive dampers, as

well as numerical and experimental results is described. The literature review has

highlighted on increased use of facades in buildings, and that some research on

facade behaviour has been carried out. However, relatively small amount of research

has been carried out on the seismic response of building facade systems fitted with

dampers. Since earthquakes are universal, the proposed project findings will have

international applications.

2.14.2. Proposed research

Research in the seismic response of concrete building facade systems with energy

absorber connections or dampers is limited and this research project was undertaken

to enable the design of concrete building facade systems, which are less vulnerable

under seismic loads and to establish appropriate connection properties. The main aim

of this research project is to generate fundamental research information on the

influence of energy absorbing connections in mitigating the seismic response of

building facade systems and then use this information to develop guidelines for safer

and more efficient facade connection design. The main parameters in this study are

given in section 2.14.1. Initially, simple three storey building facade systems are

modelled and analysed under earthquakes, using Finite Element techniques, to

establish the feasibility of the procedure. It is then extended to the investigation on

seismic mitigation of multistorey building facade system with energy absorbing

devices inserted within the building facade system. The influence of facade mass on

the structure and finally the influence of important connection parameters such as

stiffness and damping capacity are evaluated. To further broaden understanding of

damping devices embedded within the building facade system, these structures are

treated under three different earthquake excitations and the results are compared in

order to view the behaviour of the structures and to create an efficient damping

system. Only in plane stress motion of the building facade system is considered in

this investigation.


51

Chapter 3

Development of Computer Model for Building

Facade System and Feasibility Study


52

3. Development of Computer Model for building Facade

System

3.1. Introduction

This study comprehensively investigates the seismic response of multi-storey

building facade systems. Energy absorbing connections in the from of viscoelastic

(VE) dampers were used to mitigate the adverse seismic effects on the system.

Though several structural models were treated in the thesis, the 12-storey models

were the focus, especially as their natural frequencies were within the range of the

dominant modes of the selected earthquakes. The development of the computer

model for the building façade system is hence described with respect to the 12 storey

model. The computer model was validated by comparing results with those from an

existing study. Finite element techniques were employed to investigate seismic

response of these structures under the El Centro, Kobe and Northridge earthquakes

scaled to peak ground acceleration (PGA) 0.2g to suit low seismic activities in

Australia. The feasibility of the present procedure was established through the

analysis of a simpler, 3-storey building façade system with and without dampers. The

structural façade systems were mainly precast concrete and glass facades.

3.2. Description of 12-storey structural models-undamped structure

Two-dimensional 12-storey, 4 span structures were chosen to carry out the initial

study. Columns and beams of the frame had cross-sectional dimensions of 0.6 x 0.6

m and 0.65 x 0.6 m, respectively to support the gravity loads. This structure had four

spans, each of 8.0 m and the height between storeys was 4.0 m, which made the

overall height of the structure 48.0 m.

Facade panels were conveniently modelled using plane stress elements. Precast

concrete was initially chosen for the facades as they are popular in Australia and

world wide. Normally, the height of the facade wall model is equal to the floor

height. In this study the dimensions of the facade panels were 7.9 m wide, 3.9 m high

and 0.15 m thick so as to accommodate the connections. The facade panels were

placed in the second storey and onward up to the 12 storey at 0.05 m distance from

the building frame. The connection between facade and frame were modelled as


53

linear springs. Each faced panel contained a total of eight connection points, 4

vertical connections at beam ends and 4 horizontal connections to the column ends. It

was necessary to determine the desired properties of the connections in terms of

stiffness and energy absorption capacity and this will be described in the next

section. Fig. 3.1 illustrates the model of twelve storey building façade system.

Figure 3.1 Model of 12-storeys building facade system

Based on Australian and New Zealand standard (AS/NZS 1170.1: 2002) dead and

live loads were calculated and applied to the structures in the form of uniformly

distributed loads. In order to investigate the influence of load magnitude, the

following two load cases were considered.

i. Load case 1: The vertical loading on the structure was 75 kN/m applied

to the lower storey beams while the load distributed to the top storey

beam was 50 kN/m.

ii. Load case 2: The vertical loading on the structure was 40 kN/m applied

to the lower storey beams while the load distributed to the top storey

beam was 34 kN/m.


54

3.2.1. Properties of the building facade connection

Figure 3.2 shows a typical L shaped steel connection between the frame and the

precast concrete facade as used in Australia. Each of these L-shaped connections

require two bolts, one attaching the connector to the column and facade and another

the connector to the beam and facade. As evident, this connection is stiff and has no

energy absorption capacity, and hence it can cause facade failure. To enable

meaningful analysis of the building facade systems in this study, properties of the

connections between the frame and facade must be defined. The stiffness of the

connections to be modelled and analysed in the undamped structure must be

comparable to that of these bolts, while the stiffness and damping properties of

energy absorbing connections will be separately developed.

Figure 3.2 Typical L shaped connection

(Based on Precast Concrete Pty Ltd Australia, 2003)

3.2.2. Description of 12-storey structural model with energy absorbing connections

For energy absorption at the connections, VE dampers were found to be appropriate.

These dampers have proven to be reliable (Marko et al., April 2006), and their

properties are easy to evaluate. Moreover, VE dampers are easy to model in finite

element programs. With this type of energy absorbing connection, this study is able

to comprehensively investigate the influence of the damping connections on the

seismic response of the building facade systems. The 12-storey building facade

system with the properties and loads described in Sec. 3.2 with the addition of the

VE damping devices, modelled by spring (represents stiffness) and dashpot

(represents damping) in parallel was investigated. These energy absorbing

connections were placed in the horizontal direction of the structure

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55

The stiffness and damping coefficients were defined by Abbas & Kelly (1993) as

follows:

t

AGkd

′=

(1)

ωt

AGCd

′′=

(2)

Where:

A is the shear area of the VE material

t is the thickness of the VE material

ω is the loading frequency of the VE damper

G′ is the shear storage modulus, and

G ′′ is the shear loss modulus.

The following expressions were used to obtain the moduli of the Viscoelastic

material as defined by Abbas and Kelly (1993):

( )TempeG 46.7223.051.00.16 −=′ γω (3)

( )TempeG 89.7320.051.05.18 −=′′ γω (4)

where γ is the shear strain.

In order to find the optimum values of connection properties different values of

stiffness and damping were investigated. The VE damping connections were used to

determine their capacity to effectively control the, facade distortion, deformation in

connections, forces in connections and the differential displacement between frame

and facade.

In this study the most extensive investigation was conducted on medium-rise12-

storey structures (Chapter 5) where a comprehensive evaluation of properties of


56

connections was performed. The properties of the damper for these 12 storey

structures were first calculated as stiffness kd = 18 x 106 N/m and damping

coefficient Cd = 30 x 106 Ns/m based on double layer damper in parallel with

dimensions of 310 mm by 160 mm by 4 mm and the values G’ = 1,102,885 Pa and

G” = 1,525,000 Pa. These moduli were calculated using the loading frequency f =

0.84 Hz, which corresponded to the fundamental frequency of the 12 storey structure

model. Results of the free vibration analysis of the 12 storey structural model are

presented in chapter 5. Damping properties of VE dampers for the 3, 6, and 18

storey models with f = 2.38 Hz, f = 1.19 Hz and f = 0.63 Hz, respectively were

calculated in a similar manner. These frequencies would give varying values for kd

and Cd, however in order to facilitate comparisons, approximate average values of

kd = 20 x 106 N/m and Cd = 35 x 106 Ns/m respectively, were determined and used

as properties of energy absorbing connections in all the subsequent analyses for the

structures with 3, 6, 12 and 18 storeys.

Figure 3.3 Typical VE solid damper

(Based on ASCE, 1997)

3.3. Material properties

The following structural materials were used in this study:

i. Concrete used for frame and facades: the material properties of

concrete with a Compressive strength, f′c of 32 MPa, Young’s modulus,

Ec of 30,000 MPa, Density, ρ of 2400kg/m3 and Poisson’s ratio, υ of

0.2.

ii. Glass used for facade: Simax glass having a tensile strength of 35-100

MPa and Young’s modulus, E of 64,000 MPa was chosen. The

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57

allowable tensile stress was 3.5MPa and the allowable compressive

stress was up to 100 MPa. Poisson’s ratio, υ was 0.2, and density,

ρ was 2,230 kg/m3.

iii. Rubber used as a sealant at the junctions between the aluminium frame

and glass facades: the material properties of rubber with Young’s

modulus, Ec of 0.7 MPa, Density, ρ of 1000 kg/m3 and Poisson’s ratio,

υ of 0.45.

iv. Aluminium used to construct the frame which was connected directly to

the glass facades via rubber sealants: the material properties of

aluminium with a Compressive yield strength, f′c of 0.035 MPa, tensile

yield strength of 0.035 Young’s modulus, Ec of 70,000 MPa, Density, ρ

of 2700kg/m3 and Poisson’s ratio, υ of 0.33.

The structural material concrete was mainly used for 3, 6, 12 and 18 storey

structures. The structural materials glass, aluminium and rubber were used only in a

12 storey building facade system.

3.4. Loading and boundary conditions

The seismic loading applied to the structural models in this study was from existing

earthquake records. These earthquake records are time histories of horizontal ground

accelerations. The acceleration was applied in the x-direction at the base of the

structure, as shown in Fig 3.1. In order to allow for this, the boundary condition was

defined as acceleration in the x-direction in which the earthquake record was applied.

The supports at the base of the structure were modelled as a rigid joint, restrained

against translation and rotation in x, y and z directions. The vertical loading on the

structure was in the form of uniformly distributed loads applied to the beams (as

described in Section 3.2).

3.5. Input earthquake records

Earthquakes have various properties such as, duration of strong motion, range of

dominant frequencies and peak acceleration. For that reason, they will have different

influences on the structures. Three well-known earthquake records were used in this

study to certify that the selected procedure for mitigation is efficient under varied


58

sorts of excitations. The selected earthquakes were applied for only the first 20

seconds of their durations. The range of dominant frequencies as well as the duration

of the strong motion was kept unchanged. In order to achieve consistent comparison

of the response of a structural model under different earthquakes, and to suit low

seismic activities in Australia, these earthquake records were scaled down to have a

common peak ground acceleration (PGA), or maximum acceleration of 0.1g initially

and then a higher value of 0.3g.

For investigation of the dynamic response of the structural models, the following

earthquake records were selected:

i. El Centro (1940) with duration of strong motion in the range of 1.5-5.5 seconds

and dominant frequencies in the range 0.39-6.39 Hz,

Figure 3.4 The El Centro earthquake record

ii. Kobe (1995) with duration of strong motion in the range of 7.5-12.5 seconds

and dominant frequencies in the range 0.29-1.12 Hz.

Figure 3.5 The Kobe earthquake record


59

iii. Northridge (1994) with duration of strong motion in the range of 3.5-8.0

seconds and dominant frequencies in the range 0.14-1.07 Hz

Figure 3.6 The Northridge earthquake record

3.6. Finite element analysis

Finite Element (FE) methods have been employed in this research to model, analyse

and evaluate the effects of the energy absorbing connections, using VE dampers, on

the seismic response of the building facade system. The program selected for the

numerical analysis was SAP2000. This programme was used for generating the

geometry, boundary conditions and loading conditions of the model as well as

analysis. To reduce the computational effort and to simplify the modelling of

selected structures, one dimensional frame elements were selected for beams and

columns and two dimensional plane stress elements were adopted for facade panels.

In a finite element analysis, selection of mesh size and layout is critical. Usually, it is

desirable to use as many elements as possible in the analysis to improve accuracy.

However, such an analysis will require excessive computer time. In this analysis,

adequate numbers of elements were chosen for both frame and facades in order to

obtain sufficient accuracy of results without excessive use of computer time after

carrying out a convergence study.

Time history dynamic analysis was selected to obtain the response of the structure

under seismic loading. This analysis assembles the mass, stiffness and damping

matrices and solves the equations of dynamic equilibrium at each point in time. The

response of the structure is obtained for selected time steps of the input earthquake

accelerogram. To investigate the effectiveness of the VE damping connections in


60

mitigating the seismic response of the building facade system, the following

important parameters are obtained from the results of the analysis,

i. deformation of connections in terms of (extension/compression of

spring)

ii. axial forces in springs

iii. differential displacement between facade and frame

iv. the distortion of facade

The results of the above parameters were then compared with those of structural

system, without energy absorbing connections.

In order to establish the adequacy of linear analysis in this study, the 12 storey

building frame was subjected to both linear and nonlinear analyses under the El

Centro earthquake scaled to a PGA of 0.2g. The maximum tip deflections were

68.60mm and 69.72mm respectively under the linear and nonlinear analyses

respectively, confirming that linear analysis in adequate for the present study.

3.7. Verification of results

The structural control investigation is significantly diversified at present time for

definite applications and requisite objectives. It is not possible to find any guideline

for the comparison of results from various algorithms and devices. The experimental

testing under conditions nearly close to the realistic physical structure should be

verified by experimental testing for each proposed control strategy. However, it is

unrealistic to conduct an experimental study for medium or high-rise structures

because of economical reasons.

Pinelli et al., 1992 from Georgia Institute of Technology, Atlanta, GA, USA studied

the energy dissipating cladding connections for passive control of building seismic

response. They had initially studied the behaviour of the anchor system, or inserts, in

an experimental test programme. Then, a series of simple steel designs for the

connection body, or connector, were tested in a specially designed laboratory fixture.

Based on the experimental results, lumped parameter analytical models of the insert

and the connector, which closely reproduce their hysteretic characteristics were


61

conceived. To solve the problem of parameter identification, an optimization

procedure was introduced. The models of the anchors were subsequently combined

in series to simulate a complete connection system, which was incorporated into a

2D structural model of a six storey building that carries two heavy cladding panels

per bay. The structural analysis was done by using a modified version of DRAIN-2D.

The response of the structure to earthquake excitation was discussed. Time histories

of the energy demand and supply to the building, both with and without cladding,

were provided. Result show that the connector elements can be responsible for the

total hysteretic energy dissipated in the system. In order to verify the validity of the

present research project, in this study, results of the structural model of a six storey

building fitted with two heavy cladding panels per bay, that is explained in detail in

the following section, was considered.

3.7.1. Model calibration

Pinelli et al. (1992) undertook parametric studies of a 6-storey steel frame building

that was fitted with two precast cladding panels per bay. They have studied the

incorporation of metallic dampers in the connectors used to attach architectural

cladding to a building. The study structure was a ¼ scale 6-storey 3-bay moment-

resisting steel frame building constructed in the 1980s for laboratory testing at the

National Centre for Earthquake Engineering Research. For the cladding–to-frame

interaction, the test frame was provided with two precast cladding panels per bay.

The panels were considered to be rigid. Each panel was attached at its bottom to the

steel frame by two rigid bearing connectors and at its top by two advanced

connectors, which was a metallic hysteretic damper. Each bearing connector was

modelled by a simple linear elastic spring of a very high stiffness.

The advance connectors were modelled as a nonlinear translational spring element,

which could incorporate bilinear behaviour with strain hardening and inelastic

unloading. A total of 35 cases were investigated, with the stiffness of the connections

in the range (0-17512.68 kN/m = 0-100 kip/in) and the yield load of the connections

in the range (17.51-175.12 kN/m = 0.10-1kip). The optimal values of k and fy were

found to be (2890 kN/m = 16.5 kip/in) and (1.023 kN = 0.23 kip) respectively. The

total weight of the structure including cladding panels was (16672 kN = 95.2 kip).


62

Computer program DRAIN-2D was used to carry out the analysis. The El Centro

earthquake ground motions scaled down to 50 % was applied to the structure.

A nonlinear dynamic (time-history) analysis was carried out. This relatively simple

model was found to give a very satisfactory representation of the connector

behaviour observed in laboratory test. For the validity of the present research

project, the following two cases are considered:

The case that was also called the unclad structure, with the cladding connected to the

structure only at the bottom, without any cladding participation to the lateral

stiffness. (This model represents the conventional design philosophy of non

participating cladding).

The case with the optimal values of the connection stiffness (k = 2890kN/m = 16.5

kip/in) and yield load (fy = 1.023 kN = 0.23 kip), respectively.

The frequencies for the two lowest modes were computed to be 1.84 Hz and 5.77 Hz

for case 1 (unclad structure) and the frequencies of the building for the two lowest

modes were computed to be 2.27 Hz and 7.09 Hz for case 2 (structure with

cladding). Results of the comparative analyses of the upper floor displacement –time

histories for both unclad and clad structure are presented. Fig.3.7 shows the building

design model, (a) a DRAIN-2dx 2D frame model; and (b) a typical bay with panels

and connections.

Figure 3.7 NCEER 1/4-scale building design model

(Based on earthquake engineering and structural dynamic, 2002)

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63

The comparison of responses for the undamped and damped structures showed that

the advanced connectors were able to reduce peak values of upper floor

displacement. This trend was evident in some of the models treated in this thesis. In

order to verify the validity of the present research project, a similar model was

created and treated under the same earthquake excitations in the computer program

SAP2000, as explained in the following section. Time history responses of upper

floor displacement for the structure with No tie-back connections and structure fitted

with advanced connectors are illustrated in Fig. 3.8.

Figure 3.8 Upper floor displacement of structure with No tie-back connections and structure with advanced connections

3.7.2. Results of analytical investigation using the parameters of (Pinelli et. al)

The analytical model created in the computer program SAP2000 was a six storey,

three bay steel frame. The structure had the overall dimension of 5.5m in height and

2.9m wide Fig. as shown in Fig. 3.7a. The frame was provided with two precast

cladding panels per bay. The panels were considered to be rigid. Each panel was

attached at its bottom to the steel frame by two rigid bearing connectors and at its top

by two energy absorbing connectors. The bearing connections were placed in the

bottom of the panel. Each bearing connector was modelled by a simple linear elastic

spring with a very high stiffness. The energy absorbing connectors were placed at the

top of the panel. They were modelled using Link/Support Type of Plastic (Wen) with

Nonlinear Directional Properties option. The optimal value of k and fy were (2890

kN/m = 16.5 kip/in) and (1.023 kN = 0.23 kip). The columns and beams were


64

modelled from solid steel and were made of steel profiles S 3 x 5.7 types. To adjust

natural frequencies to 2.27 and 7.09 Hz, additional lumped mass was applied at each

beam-column joint. The results of upper floor displacement for the structure with and

without energy absorbing connection, obtained by analytical models in computer

program SAP2000 are presented below. Time history responses of upper floor

displacement for the structure with No tie-back connections and structure fitted with

energy absorbing connectors under the El Centro earthquake excitations (scaled to 50

%) are illustrated in Fig. 3.9.

3.7.3. Results of analytical investigation for the optimum connections properties spring (kd = 20,000 kN/m) and dashpot (Cd = 35000 kN/m)

This Fig. shows that the analytical model has the same beam and column size as the

material properties and loads as described above was considered. Each bearing

connector was modelled by a simple linear elastic spring with a very high stiffness as

before. In this study the energy absorbing connections at the top were modelled as a

link support type of damper with linear directional properties. They were modelled

by spring and dashpot in parallel. The optimal value of kd and Cd were 20,000 kN/m

and 35,000 kNs/m respectively. The El Centro earthquake excitation (scaled to 50 %)

was applied. The results of upper floor displacement for the structure with and

without energy absorbing connection, obtained by analytical models in computer

program SAP2000 are presented below. Fig. 3.9 illustrates the time history responses

of upper floor displacement for the undamped structure and structure fitted with

dampers.


65

Six-Storey Steel Frame

-50.8

-40.8

-30.8

-20.8

-10.8

-0.8

9.2

19.2

29.2

39.2

0 2 4 6 8Time (Sec)

Upper Flo

or D

ispla

cem

ent(m

m)

No tie-back connections AD connections VE connections

Figure 3.9 Upper floor displacement for structure with no tie-back connections

and structure fitted with advanced and VE damping connections

Fig. 3.9 shows that comparing upper floor displacement, obtained from computer

program SAP2000 with results from computer programme DRAIN-2D, in terms of

upper floor displacement the results were in reasonably good agreement and in all the

cases followed similar trends.

As stated previously, it is not possible to carry out suitable experimental tests of

multi-storey structures under seismic conditions due to economic and logistical

problems. Therefore, in the present investigation, the validity of the method used

was confirmed on the test model. Due to the unavailability of some structural details,

it was not feasible to exactly model the test structure. In spite of this, the present

computer results agreed well with those from the literature study and verified the

validity of the considered method. For convenience results of both computer

programmes are presented in Table 3.1.


66

Table 3.1 Comparison of maximum (upper floor) deflections

Pinelli et al. 30.00

Present results using Pinelli's properties 33.00

Present results with optimum damper properties 31.80

Comparison of Maximum (Upper Floor) Deflections (mm)

3.8. Analysis of 3-storey building facade system and feasibility study

3.8.1. 3- Description of 3-storey frame structural model

A two-dimensional 3-storey, single span concrete frame was chosen to carry out the

feasibility study. The overall dimensions of this building frame were 12 m high and 8

m wide. The beams were 0.45 m deep and 0.35 m wide. The cross-sectional

dimensions of the columns were 0.35 m x 0.35 m. The height between storeys was

set at 4.0 m, as seen in Fig. 3.10, which made the overall height of the structures 12.0

m.

Figure 3.10 3- storey concrete frame

3.9. 3-storey building facade system structural model

In this investigation, the 3-storey building structural model fitted with facade, was

first considered without energy dissipating connections (undamped structure), and

then with energy dissipating connections (damped structure). Both structures, with

and without damping devices, were analysed under the same earthquake excitations.


67

3.9.1. Description of 3-storey structural model - undamped structure

The 3-storey frame with the properties described above with the addition of facades

is considered. Facade panels were suitably modelled using plane stress elements as

discussed earlier. The dimensions of the facade panels were 7.9 m wide, 3.9 m high

and 0.15 m as before. The facade panels were placed in the second and third storeys

at 0.05 m distance from the building frame. The connection between facade and

frame were modelled as linear springs. Dead and live loads of 75 kN/m in a form of

uniformly distributed loads were applied to the first and second storey beams while

the load distributed to the third storey beam was 50 kN/m (Load Case 1). Fig.3.11

shows the 3- storey concrete frame with facade panels

.

Figure 3.11 3-storey concrete frame with facade panels

The natural frequency and period of vibration of 3 storey structure is displayed in

Table 3.2.

Table 3.2 Natural frequencies of 3-storey structure

3- Storey Concrete Frame

Modes Natural

Frequency(Hz) Period of Vibration(T/Sec) First 2.38 0.42

Second 7.44 0.13 Third 12.41 0.08


68

3.9.2. Description of 3-storey structural model with energy absorbing connections

The 3-storey building facade system with the properties and loads described in Sec.

3.10.1 with the addition of the VE damping devices, modelled by spring (represents

stiffness) and dashpot (represents damping) in parallel was investigated to establish

the feasibility of the procedure used in this study. These energy absorbing

connections as discussed earlier were placed in the horizontal direction of the

structure as shown in Fig.3.12.

Figure 3.12 3-Storey building facade system with spring-dashpot connections

3.10. Seismic responses of 3-storey undamped structure with precast concrete facade - effect of spring stiffness

In order to study the effect of spring stiffness in an undamped structure, first, a 3-

storey structure as described in Section 3.10.1 was considered. The vertical

connections should be able to support the mass of the facades and provide minimum

deformation. The mass of the facade was calculated to be 113.011 kN. The stiffness

of the vertical connections k was chosen as 35,000 kN/m. Assuming 4 spring

supports, (113.011 / 4 x 35,000) x 1000 = 0.85 mm is approximate spring

deformation., which is quite reasonable. The stiffness of horizontal connections was

varied in the range 5,000-30,000 kN/m. The seismic load applied to the structural

system was horizontal and therefore, in this study only the behaviour of the

horizontal connections was considered. The effect of the connection stiffness on the


69

seismic response of the structural system, under the El Centro earthquake was

investigated. Table 3.3 display the maximum values of the response quantities, for

deformation and force in connections, differential displacement between frame and

facades and the distortion of facades under the El Centro earthquake excitation (with

PGA scaled to 0.1g).

Table 3.3 Maximum values of the response quantities, considering horizontal connections stiffness

5000 4.82 24.12 4.88 5.75E-0410000 3.55 35.50 3.63 4.37E-0415000 3.37 50.55 3.31 4.11E-0420000 3.12 62.43 3.23 4.18E-0425000 2.82 70.53 2.97 3.85E-0430000 2.52 75.77 2.67 3.51E-04

3-Storey Concrete Frame Fitted with Facades

Stiffness kN/m

Deformation (mm) Force (kN)

Differential Displacement

(mm)Distortion (Radian)

The results of the analysis showed that horizontal stiffness of the connection had

only a small effect on the seismic response of the structure when only moderate

variations in all investigated parameters were obtained. Hence the (common value

of) horizontal stiffness of kd = 20,000 kN, as discussed in section 3.2.2, was selected

for future modelling and analyses.

3.11. Seismic responses of 3- storey structure with precast concrete facade - effect of energy absorbing connection

A 3-storey structure as described in Section 3.10.2 was considered. This structure

was analysed under 2 different conditions.

i. The value of spring stiffness was after preliminary study determined to

be 20,000 kN/m (as discussed above). The values of dashpot damping

were in the range 15,000 - 50,000 kNs/m.

ii. The value of spring stiffness was in the range 5,000 - 35,000 kN/m. The

value of dashpot damping was 35,000 kNs/m.


70

A dynamic analysis of this structure with VE damping connections placed in the

second and third storeys was conducted under the El Centro earthquake excitations

scaled to peak ground acceleration (PGA) 0.1g. The connection was modelled as

elastic spring and dashpot in parallel, as described in Section 3.3.3. As before, a

stiffness of 35,000 kN/m was chosen for the vertical connection. The values of spring

stiffness for the horizontal connection were set to be 20,000 kN/m and the values of

dashpot damping were in the ranged from 15,000 - 50,000 kNs/m based on

preliminary calculations. The seismic loading applied to the structural system was

horizontal, therefore, in this study only the behaviour of the horizontal connections

was considered. The effect of the connection stiffness and damping on the seismic

response of the structural system was investigated. The response of the structure is

obtained for selected time steps of the input earthquakes accelerogram.

Important results pertaining to the reductions in the peak values for the deformation

of connections, axial force in connection, differential displacement between frame

and facades and the distortion of facades under the scaled El Centro earthquake

excitations are summarised in Table 3.4. The results of reduction in all investigated

parameters of the structure embedded with VE damping connections of varying

properties display overall very high performance. The results reveal the high level of

sensitivity of the structure to diverse damping properties. The best performance with

the highest reduction in all investigated parameters was recorded for dashpot with

damping parameter of Cd = 40,000 kNs/m. The results showed that the damping

parameter of 40,000 kNs/m caused the lowest values of deformation in connections

and differential displacement of 0.71mm and 0.73mm respectively. Similarly, the

distortion of facade was as small as 0.000055 radian. The damping parameter of

50,000 kNs/m also showed similar results. The next highest reductions were

recorded for dashpot with damping parameter of Cd = 35,000 kNs/m.

As seen from Table 3.4, the reductions in all investigated parameters were only

slightly different to the values reported earlier (for the damping parameter of 40,000

kNs/m). A deformation of 0.72 mm for connections and differential displacement of

0.74 mm between the frame and facade was experienced for dashpot with damping

parameter of Cd = 35,000 kNs/m. Similarly, the facade distortion of 0.000057 radian

was achieved. It may be concluded that the previously (in section 3.3.3) chosen


71

value for the damping parameter of Cd = 35,000 kNs/m is quite appropriate as

damping values beyond this did not show any appreciable improvement in results.

Table 3.4 Maximum values of the response quantities, considering connections stiffness kd and damping coefficient Cd

20000 15000 1.26 25.2 2.07 1.00E-0420000 20000 1.05 21 1.1 8.25E-0520000 25000 0.88 17.6 0.91 6.75E-0520000 30000 0.78 15.6 0.82 6.25E-0520000 35000 0.72 14.4 0.74 5.75E-0520000 40000 0.71 14.2 0.73 5.50E-0520000 45000 0.71 14.2 0.73 5.50E-0520000 50000 0.71 14.2 0.73 5.50E-05


StiffnesskN/m

Damping kNs/m

Deformation (mm)

Force (kN)



A 3-storey structure with the same load and properties as before was considered. At

this stage of the investigation, the values of spring stiffness were varied in the range

from 5,000 - 35,000 kN/m, while the damping parameter of Cd = 35,000 kNs/m was

kept constant. The main purpose of this exercise was to study the effect of the

horizontal spring stiffness (kd ) on the behaviour of the structure. A summary of the

results indicating reductions in the deformation of connections, axial force in

connection, differential displacement between frame and facades and the distortion

of facades under the El Centro earthquake excitations, are summarised in Table 3.5.

In general, the results showed good seismic control of the facade deformation with

respect to all investigated parameters for the range of stiffness 5000 - 20,000 kN/m.

However, an increase in the stiffness of the springs over the value of 20,000 kN/m

resulted in increases in the value for all investigated parameters. As can be seen in

Table 3.4, the best performance of the structure for all investigated parameters was

achieved when the spring stiffness (kd) was 20,000 kN/m.


72

Table 3.5 Maximum values of the response quantities considering connections stiffness kd and damping coefficient Cd

5000 35000 1.56 31.2 1.56 2.75E-0510000 35000 1.11 22.2 1.13 4.25E-0515000 35000 0.86 17.2 0.88 5.25E-0520000 35000 0.72 14.4 0.74 5.75E-0525000 35000 0.75 15.1 0.81 7.25E-0530000 35000 0.81 16.1 0.85 9.75E-0535000 35000 0.83 16.6 0.88 1.18E-04




StiffnesskN/m

Damping kNs/m

Deformation (mm)

Force (kN)

With regards to the investigated parameters, clearly the best results occurred when

stiffness of the spring was 20,000 kN/m. In general, the results from the analysis

showed that the influence of the stiffness (kd) was not very significant for the

optimum value of the dashpot damping (Cd) used in this part of the investigation.

The connection realised by spring (k) had only a small effect on the seismic response

of the structure, when only moderate reductions for all investigated parameters were

obtained. The results reveal the high level of sensitivity of the structure to diverse

damping properties of dashpot. The best performance with the highest reduction in

all investigated parameters was recorded for dashpot with damping a parameter of

Cd = 40,000 kNs/m. The second highest reductions were recorded for dashpot with a

damping parameter of Cd = 35,000 kNs/m with the reductions in all investigated

parameters only slightly different to the values obtained for the damping parameter

of 40,000 kNs/m.

When the algorithm of (Abbas and Kelly, 1993) see Section 3.3.3 was used to

evaluate the connections properties, the values of Cd = 35,000 kNs/m, and kd =

20,000 kN/m were obtained. The present investigation revealed that the best results

with the highest reduction in all investigated parameters occurred when the value of

spring stiffness was 20,000 kN/m and a value of dashpot damping of 40,000 kNs/m

was employed. When the dashpot damping was changed to 35,000 kNs/m, there was

an only marginal difference in the results. To make the present connection properties

compatible with the values from Abbas and Kelly and match those established for

other structures (section 3.3.3), it was decided to use Cd = 35,000 kNs/m, and kd =


73

20,000 kN/m, in all future analyses with precast concrete facades. The results from

the seismic analysis of the structure fitted with the VE damping connections will be

compared with those of the undamped structure in the following section.

3.12. Seismic response of 3-storey structure with precast concrete façade - undamped structure and structure with VE connections

The same 3-storey structure with the load and properties as before is considered. At

this stage of the investigation, the values of spring kd = 20,000 kN/m and dashpot

damping Cd = 35,000 kN/m as explained before were chosen. The effect of the

connection stiffness and damping on the seismic response of the structural system

was investigated. The response of the structure is obtained for selected time steps of

the input earthquake’s accelerogram scaled to PGA of (0.1g).

The typical time history responses of the deformation of connections, the axial forces

in connections, the differential displacements between frame and facade and the

distortion of facades under the El Centro earthquake excitations are presented in Fig.

3.13 - 3.16 These Figs. clearly demonstrates the influence of energy absorbing

connections. While the analysis of the structures was completed over the initial 20

seconds of the earthquake, the Fingers below show only the critical first 7 seconds in

order to display more clearly the behaviour of the structures in this time period. In all

simulations, after the 7 second point, all the parameters that were studied displayed

insignificant values that gradually decreased to negligible values by 20 seconds. For

this reason, the analysis presented below focuses on the initial 7 seconds of the

simulations.

In these figures “Low.F.VE”, represent lower façade with VE damping connection

located in the lower part of the façade panel and “Upp.F.VE”, represent upper façade

with VE damping connection located in the lower part of the façade panel, while

“Low.Fa.L.C”, represent lower façade connections located in the lower part of the

façade panel and “Upp.Fa.L.C”, represent upper façade connections located in the

upper part of the façade panel.


74

3-Storey Concrete Frame

-3

-2

-1

0

1

2

3

4

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Time (Sec)

De

form

ati

on

(mm

)

Lo w.F-VE Upp.F-VE Lo w. Fa .L.C Upp. Fa.L.C

Figure 3.13 3-storey structure with and without VE damping connections, time histories of deformation in upper and lower connection of facade

As can be seen from Fig 3.13, the deformation of the lower connections of the

second storey and lower connections of the third storey, between frame and facade

under the El Centro earthquake excitation, for the undamped structure were limited

to a short time interval of about 4.5 seconds with a magnitude of 3.12 mm and 1.39

mm respectively. However, the incorporation of the VE damping connection to the

structure resulted in significant reduction in the deformation of connections at the

same time interval of about 4.5 seconds by up to 76.9 % and 82 % respectively. It is

evident that the second storey experienced the largest deformation in connections for

both the undamped and the structure with VE damping connections, despite the fact

that, a significant reduction in the deformation of connections for both structures

were perceived in the third storey. Furthermore, it can be seen that after

approximately 1.8 seconds the undamped structure began to significantly increase the

deformation in connections. The increase is continued up to second 5 and then once

again begins to decrease. The time history of the structure with VE damping

connections and the undamped structure clearly showed that, while the magnitude of

the deformations increased in the undamped structure, the pattern of movement over

the 7 seconds was the same for both structures. A similar phenomenon can be seen in

Figs. 3.14- 3.16


75

Time history responses of axial forces under the El Centro earthquake excitation in

the undamped structure and in the structures with the VE damping connections

placed horizontally in the second and third storeys are illustrated in Fig. 3.14.


-60

-40

-20

0

20

40

60

80

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7

Time (Sec)

Fo

rce

(kN

)

Lo w.F-VE Upp.F-VE Lo w.F-UN UpP .F-UN

Figure 3.14 3- storey structure with and without VE damping connections, time histories of force in upper and lower connection of facade

The graphs show high efficiency of the VE damping connections in the upper storey

lower connection. As can be seen from Fig 3.14, the axial forces in the lower

connections of the second storey and lower connections of the third storey, for the

undamped structure were 62.46 kN and 27.13 kN, respectively. Whilst with the

insertion of the VE damping connections to the structure, the forces in the lower

connections of the second storey and lower connections of the third storey, between

frame and facade were significantly reduced by up to 76.9 % and 81.3 %

respectively. The graph once again shows that the maximum values of deformation

occurred only during short time intervals of about 4.5 sec, for both the undamped

structure and structure with the VE damping system. Fig. 3.10 showed that the VE

damping connections consistently reduced the axial forces response of the building

facade system.

In Fig. 3.15, the results show that the differential displacement between the frame

and second storey facade as well as the frame and the third storey facade for the

undamped structure were 3.23 mm and 1.42mm respectively. While the inclusion of

the VE damping connection to all horizontal connections between the frame and


76

facades, resulted in differential displacement reduction by up to 77 % between the

frame and second storey facade and 82 % between the frame and third storey facade.


-3.5-3

-2.5-2

-1.5-1

-0.50

0.51

1.52

2.53

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Time (sec)

Diff

ere

ntia

l Dis

pla

cem

en

t (m

m)

Upp.F-UN Low.F-UN Low. F-VE Upp. F-VE

Figure 3.15 3-storey structure with and without VE damping connections time histories for differential displacement between frame and facade

The graph again showed very high efficiency of the VE damping connections in the

upper storey. As can be seen from Fig. 3.15, the differential displacement between

frame and facade in the second storey is larger than the differential displacement

between frame and facade in the third storey in both undamped and structure

entrenched with VE damping connections. This can be attributed to the weakness of

the storey that has no facade panel. The maximum values of differential displacement

between frame and facade occurred only during short time intervals of about 4.5 sec,

for both the undamped structure and structure with VE damping system.

As can be seen from Fig. 3.16, the VE damping connection achieved a very high

level of efficiency. The maximum values of distortion occurred only during short

time intervals of about 4.5 sec. In addition, after approximately 1.8 seconds of the El

Centro earthquake, the undamped structure began to significantly increase the

distortion of facades in the second and third storey of the structure. The increase is

continued up to second 5 and then once again begins to decrease rapidly.


77


-0.0005-0.0004-0.0003-0.0002-0.0001

00.00010.00020.00030.0004

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

Time (sec)

Dis

tort

ion

(Ra

dia

n)

Upp.F-UN Lo w.F-UN Lo w. F-VE Upp. F-VE

Figure 3.16 3-storey structure with and without VE damping connection, time histories of distortion of facades

A similar phenomenon can be seen from the results of the structure with VE damping

connections where the response of the structure is significantly reduced. As can be

seen from Fig.3.16, the distortion of facade in the second and third storey for the

undamped structure was recorded to be 0.00041 and 0.000218 radian respectively.

However, the incorporation of the VE damping devices to all horizontal connections

between the frame and facade resulted in considerable distortion reduction by up to

86.1 % and 87.2 % respectively. The results show that the VE damping connections

experienced highest reduction in the distortion of facade almost equally in both

storey levels of the structure.

Important parameters such as the maximum deformation and forces in connections,

the differential displacements between the facade and frame, distortion of facade and

interstorey drifts, under the El Centro earthquake excitation were investigated. Fig.

3.13 - 3.16 showed that the VE damping connections consistently reduced all

investigated parameters of the building facade system by a great margin. In addition,

all peak values occurred only during a short time intervals of about 4.5 sec, for both

the undamped structure and structure with the VE damping system. After

approximately 1.8 seconds of the El Centro earthquake, the undamped structure

began to significantly increase the deformation in connections. The increase

continued up to second 5 and then once again began to decrease rapidly. The time

history of the structure with VE damping connections, and undamped structure


78

remained with the same trend throughout the duration of the excitation. In general

the damping system in the structure revealed a substantial reduction in the seismic

response of the building facade system. The same 3-storey structure with the load

and properties and values of spring kd = 20,000 kN/m and dashpot damping Cd =

35,000 kN/m as explained before were considered. The effect of the connection

stiffness and damping on the seismic response of the structural system under the El

Centro, Kobe and Northridge earthquakes was investigated.

Figs. 3.17-3.20 show comparisons between the damped response of the structure

with the undamped structure under the El Centro, Kobe and Northridge earthquakes.

They illustrate the maximum responses in terms of deformations and forces in

connections, differential displacements between frame and facade, interstorey drifts,

as well as distortion of facades. Additional results can be found in Appendix A. In

these Figures UN and VE denote the results of the undamped and damped systems

respectively.

Fig. 3.17 displays an efficiency of the damping systems in reducing the deformation

of connections under a variety of earthquake loadings. From the results it can be

stated that the deformation of connection in the second storey was larger than the

deformation of the connections in the third storey in both the undamped and the

structure with VE damping connections, under all selected earthquakes. The

incorporation of the VE damping connections in the structure consistently reduced

the deformation of connections response under the selected earthquake records in a

significant manner. As can be seen in Fig 3.17, the deformation of connection

experienced under the El Centro earthquake for the undamped structure was 3.12mm.

However with the insertion of the VE damping connections in the structure the

deformation of connections were reduced by up to 76 %. Again a very high

efficiency of the VE damping connections was achieved in the case of the Kobe

earthquake. The deformation of connection experienced under the Kobe earthquake,

for the undamped structure was 4.65mm.


79


0

1

2

3

4

5

S.2 S.3 S.2 S.3 S.2 S.3

El-Centro Kobe Northridge

Building Storey

De

form

atio

n (

mm

)

UNVE

Figure 3.17 3-storey structure with and without VE damping connections, maximum deformation in connection

The result showed that with the insertion of VE damping connections in the

structure, the deformation of connections were reduced by as much as 79 %. A

similar trend was observed in the case of the Northridge earthquake. The results

showed that the deformation of connection experienced under the Northridge

earthquake, for the undamped structure was 3.21mm. However after the VE damping

connections were fitted in the structure the deformation of connections was reduced

by up to 70 %.

It can be seen in Fig. 3.17, that the VE damping connections achieved excellent

reductions in deformation for all of the earthquake excitations with the reductions

being slightly higher in the Kobe earthquake excitation than the other two.

Fig. 3.18 displays the maximum reduction in the axial forces in connections under

the selected earthquakes for the undamped structure and structures embedded with

VE damping connections. As can be seen from this figure, the greatest reduction in

the axial forces in connections was achieved under the Kobe earthquake.


80


0

20

40

60

80

100

S.2 S.3 S.2 S.3 S.2 S.3


Building Storey

For

ce (

kN)

UN

VE

Figure 3.18 3- storey structure with and without VE damping connections, maximum forces in connections

The results show that the maximum axial forces in connections experienced under

the Kobe earthquake, for the undamped structure was 93.11 kN. However, the

insertion of VE damping connections in the structure improved the ability to reduce

the axial forces in the connections by as much as 79%. The second highest reduction

in the axial forces in connections occurred under the El Centro earthquake. The

maximum axial force in the connections under the El Centro earthquake, for the

undamped structure was 62.64 kN. On the other hand with the insertion of VE

damping connections in the structure the axial forces in the connections were

reduced by up to 76 %. Results of structure obtained under the Northridge

earthquake, were insignificantly lower than the Kobe and El Centro earthquakes.

The maximum axial forces in connections experienced under the Northridge

earthquake, for the undamped structure was 64.34 kN. However with the inclusion of

VE damping connections in the structure the axial forces in connections were

reduced by up to 70 %. In general, the results showed that the incorporation of the

VE damping connections in the building facade system improved the steadfastness of

the energy absorption and reduced the seismic effect on the all levels of the structure.

Fig. 3.19 illustrates the maximum differential displacement reduction between the

frame and facade experienced under the Kobe, El Centro and Northridge

earthquakes. As can be seen from this Fig. the maximum differential displacements

between the frame and facade experienced under the Kobe, El Centro and Northridge


81

earthquakes, for the undamped structure were 3.23mm, 4.88mm and 3.34mm

respectively. However the insertion of VE damping connections to the structure

displayed very high efficiency in the reduction of differential displacement between

the frame and facade.


0

1

2

3

4

5

S.2 S.3 S.2 S.3 S.2 S.3


Building Storey

Diff

ern

tial D

isp

lace

me

nt

(mm

)

UN

VE

Figure 3.19 3-storey structure with and without VE damping connections, maximum differential displacement between frame and facade

The highest differential displacement with a reduction of 79 % was achieved under

the Kobe earthquake excitation and only a slightly lower reduction of 77% was

experienced under the El Centro earthquake excitation.

The differential displacement reduction that occurred for the Northridge earthquake

was lower with an average of 70%. From the result of this analysis, it can be

concluded that the inclusion of VE damping connections in the structure produced

the greatest reduction in the differential displacement between the frame and facade.

Fig.3.20, explains the distortion of facades experienced under the El Centro

earthquake, in the undamped and structure fitted with VE damping connections. The

results show that the highest reduction in the distortion was recorded under the El

Centro and Kobe earthquake. The reductions under the Northridge earthquake were

also adequately high.

Fig. 3.20 illustrates that, the distortion of facades experienced under the El Centro

earthquake, in the undamped structure was 0.0004175 radian. However, the

incorporation of VE damping devices to the structure reduced the distortion of facade


82

considerably by up to 86.2%. Fig 3.20 also indicates that the distortion of facades

experienced under the Kobe earthquake excitation, for the undamped structure, was

0.00061 radian. With the insertion of VE damping connections to the structure, the

distortion of facades was reduced by the same amount of up to 87.7 % as the

distortion experienced under the El Centro earthquake.


0

0.0001

0.0002

0.00030.0004

0.0005

0.0006

0.0007

S.2 S.3 S.2 S.3 S.2 S.3


Buildinig Storey

Dis

tort

ion

(R

adia

n)

UN

VE

Figure 3.20 3-storey structure with and without VE damping connections, maximum distortion of facade

Similarly, the distortion of facades under the Northridge earthquake excitation, for

the undamped structure was 0.0000425 radian. On the other hand, after the VE

damping connections were introduced to the structure, the distortion of facades was

dramatically reduced by up to 83.7 %. In general, the VE damping connections

displayed a significantly higher efficiency in most cases under the El Centro, Kobe

and Northridge earthquakes.

In general, the results of the investigation of the damping system have demonstrated

an ability to reduce the seismic response of buildings by placement of damping

devices within the building facade system. Fig 3.17-3.20 clearly demonstrate that the

incorporation of VE damping connections to the structure have significantly changed

the effect of the seismic loading on the behaviour of the building facade system and

produced desirable results. A substantial reduction in value in all parameters can be

observed from the previous graphs and charts. There were varying degrees of

effectiveness of this damping system for the various earthquake records studied. The

structural response was, however, shown to be better with the VE damping


83

connections included in the structural system than without them. This efficiency

could be due to the varying intensities and frequency content of the earthquake, and

their impact on the VE damping connections. The results showed that the highest

reduction in all investigated parameters was achieved under the Kobe earthquake.

3.13. Seismic responses of 3- storey undamped structure and structure with VE connections under higher seismic loads

To test the feasibility, the same structure was analysed under the 3 earthquake

records with a higher PGA of 0.3g. 3-storey building facade systems with the

parameters, material properties and loads as described in Section 3.10.1 and 3.10.2

were considered. The selected earthquake records were scaled to PGA of 0.3 g. Fig.

3.21 displays an efficiency of the damping systems in reducing the deformation of

connections under a variety of earthquake loadings.

From the results it can be stated that the deformation of connection in the second

storey was larger than the deformation of the connections in the third storey in both

the undamped and the structure with VE damping connections, under all selected

earthquakes. The incorporation of the VE damping connections in the structure

consistently reduced the deformation of connections response under the selected

earthquake records in a significant manner.

Results are presented in the following sections when the values within brackets

indicate value under PGA 0.1g. As can be seen in Fig 3.17, the deformation of

connection experienced under the El Centro earthquake for the undamped structure

was 9.37mm (3.12 mm). However with the insertion of the VE damping connections

in the structure the deformation of connections were reduced by up to78 % (76 %).

Again a very high efficiency of the VE damping connections was achieved in the

case of the Kobe earthquake. The deformation of connection experienced under the

Kobe earthquake, for the undamped structure was 13.7mm (4.65 mm). The result

showed that with the insertion of VE damping connections in the structure, the

deformation of connections were reduced by as much as 80% (79 %).

A similar trend was observed in the case of the Northridge earthquake. The results

showed that the deformation of connection experienced under the Northridge

earthquake, for the undamped structure was 10.72mm (3.21 mm). However after the


84

VE damping connections were fitted in the structure the deformation of connections

was reduced by up to 70 % (70 %).

3-storey concrete frame

02468

101214

S.2 S.3 S.2 S.3 S.2 S.3


Building storey

De

form

ati

on

(m

m)

UN

VE

Figure 3.21 3-storey structure with and without VE damping connections, maximum deformation of connection

It can be seen in Fig. 3.21, that the VE damping connections achieved excellent

reductions in deformation for all of the earthquake excitations with the reductions

being slightly higher in the Kobe earthquake excitation than the other two. In these

Figures UN and VE denote the results of the undamped and damped systems

respectively.

Fig. 3.22 illustrates the maximum differential displacement reduction between the

frame and facade experienced under the Kobe, El Centro and Northridge

earthquakes. As can be seen from this Fig. the maximum differential displacements

between the frame and facade experienced under the Kobe, El Centro and Northridge

earthquakes, for the undamped structure were 11.17, 9.7 and 5.42 mm (3.23, 4.88

and 3.34 mm) respectively. However the insertion of VE damping connections to the

structure displayed very high efficiency in the reduction of differential displacement

between the frame and facade. The highest differential displacement with a reduction

of 82% (70%) was achieved under the Northridge earthquake excitation and only a

slightly lower reduction of 78% (77%) was experienced under the El Centro

earthquake excitation. The differential displacement reduction that occurred for the

Kobe earthquake was lower with an average of 70.36% (79%).


85

3-storey concrete frame

02468

10121416

S.2 S.3 S.2 S.3 S.2 S.3


Building storey

Diff

ere

nti

al d

isp

lace

me

nt (

mm

)

UN

VE

Figure 3.22 3-storey structure with and without VE damping connections, maximum differential displacement between frame and facade

From the result of this analysis, it can be concluded that the inclusion of VE damping

connections in the structure produced the greatest reduction in the differential

displacement between the frame and facade.

3.14. Seismic responses of 3- storey structure with glass facades - effect of spring stiffness and dashpot damping

A 3-storey structure frame having the same properties and loads as described in

Section 3.10.1 (Undamped structure) and Section 3.10.2 (structure with VE damping

connections) were considered. The facade panels placed in the second and third

storey of the structure was made of glass. Each storey contained a total of 8 glass

facades measuring 2 m x 2 m with a thickness of 0.012 m. Uniformly distributed

loads of 40 kN/m were applied to the first and second storey beams while a load

distributed to the third storey beam was reduced to 34 kN/m. The model was

analysed under the El Centro earthquake excitations scaled to 0.1g. Firstly, the effect

of the connection stiffness on the seismic response of the structural system was

investigated and then the building facade system fitted with the VE damping device

was analysed to investigate the effectiveness of the energy absorbing connections. In

this study 3 different conditions were considered:

i. Stiffness of horizontal connections (k) for the undamped structure

ranging from 5,000 - 30,000 kN/m.


86

ii. Stiffness of horizontal connections (kd) kept of 5,000kN/m and values

of dashpot damping (Cd) ranged from 5,000 - 40,000 kNs/m.

iii. Stiffness of horizontal connections (kd) ranged from 5,000 - 30,000

kN/m. Values of dashpot damping (Cd) kept constant at 25,000 kNs/m.

The vertical connections for both structures were kept at the stiffness value of

35,000kN/m. The seismic load applied to the structural system was horizontal,

therefore, only the behaviour of the horizontal connections was considered. Both

undamped and damped structures with the above mentioned conditions (1-3) were

analysed under the El Centro earthquake, one at a time, to compare the results.

Table 3.6 summarises the results of the peak values for the deformation of

connections, axial force in connection, differential displacement between frame and

facades and stress in facades for the undamped structure. The spring stiffness ranged

from 5,000 to 30,000kN/m. The results reveal that most of the parameters under

investigation depend little on the change in the stiffness of the spring. From these

results it can be seen that deformation, differential displacement were decreasing

with increasing values of spring stiffness. On the other hand, in the case of the stress

in facade panels, the reverse trend was observed. So, while a stiffness value of

30,000kN/m resulted in the lowest values for almost all investigated cases, stress in

the facade panel was the highest of any of the simulated conditions (15.4 MPa). For

this reason, despite the excellent values in the other parameters, a stiffness of

30,000kN/m was not chosen as the stiffness value for further investigation of

building facade system with glass facades. The maximum allowable stress in the

glass used in this investigation was 3.5 MPa. It was determined, therefore that the

connections with a stiffness value of 5,000 kN/m, which produced a stress of 9.10

MPa, were the lowest of any of the simulated conditions at this stage of the study.


87

Table 3.6 Maximum values of the response quantities, considering connections stiffness

The results for the same investigated parameters obtained by the 3-storey frame

structure with a connection realised by spring and dashpot in parallel under the El

Centro earthquake excitation are presented in Table 3.7. The parameter of the spring

was 5,000 kN/m for all investigated cases, while values of the dashpot ranged from

5,000 to 40,000 kNs/m. From the results it can be seen that in the range of dashpot

values 5,000 - 25,000 kNs/m, its efficiency regularly increased for all investigated

parameters. On the other hand, increase in dashpot over the value 25,000 kNs/m had

no effect on additional improvement of structural response.

Table 3.7 Maximum values of the response quantities, considering connections stiffness and damping coefficient

5000 3.71 18.56 3.89 9.10 10000 2.43 24.32 2.60 11.90 15000 1.79 26.85 1.92 14.00 20000 1.40 28.18 1.56 14.00 25000 1.16 29.05 1.31 15.40 30000 0.98 29.61 1.15 15.40

3-Storey Concrete Frame with Glass Facade

Stiffness kN/m

Deformation (mm)

Force (kN)


(mm) Stress (Mpa)

Damping kNs/m

5000 5000 1.34 6.70 1.39 3.365000 10000 0.96 4.80 0.98 2.385000 15000 0.72 3.60 0.73 1.825000 20000 0.56 2.80 0.56 1.405000 25000 0.54 2.70 0.54 1.405000 30000 0.54 2.70 0.54 1.405000 35000 0.54 2.70 0.54 1.405000 40000 0.54 2.70 0.54 1.40


Stiffness kN/m

Deformation (mm)

Force (kN)


(mm) Stress (Mpa)


88

The results for the same three-storey building facade system with glass panels where

the connections between frame and facade was modelled by spring and dashpot of

different values are presented in Table 3.8. In this case damping of the dashpot was

kept constant at the value of 25,000kNs/m while investigated stiffness of the spring

was in the range 5,000-30,000 kN/m. It can be clearly seen from Table 3.8, that the

best results were once again obtained when the stiffness of the spring was

5,000kN/m. It is also evident that the consequent increase in this value of spring

resulted in a regular increase in all investigated parameters.

Table 3.8 Maximum values of the response quantities considering connections stiffness and damping coefficient

When the algorithm of (Abbas and Kelly, 1993) see Section 3.3.3, was used to

evaluate the connections properties, the values of Cd = 7,800 kNs/m, and kd = 4710

kN/m were obtained. These values which will fall in the range of average values of

kd = 5000 kN/m and Cd = 5,000 - 10,000 kNs/m respectively, were determined. The

present investigation revealed that the best results with the highest reduction in all

investigated parameters occurred when the value of spring stiffness was kd = 5,000

kN/m and a value of dashpot damping of 25,000 kNs/m were employed. When the

dashpot damping was changed to 20,000 kNs/m, there was an only marginal

difference in the results. Connections with properties determined from the theory of

Abbas and Kelly did perform well and avoided cracking of the glass panels.

However considering the results displayed in Table 3.8, and to minimise the stress

even more in the glass facade it was decided to use kd = 5,000 kN/m and Cd =

20,000 kNs/m in further analyses in a 12-storey structure with glass facades. These

connection properties will offcourse require a bigger shear area of the VE damper.

5000 25000 0.54 2.70 0.54 1.4010000 25000 0.62 6.20 0.65 3.0815000 25000 0.62 9.30 0.68 4.9020000 25000 0.57 11.40 0.63 6.3025000 25000 0.56 14.00 0.64 7.0030000 25000 0.56 16.80 0.66 8.40


Stiffness kN/m

Damping kNs/m

Deformation (mm)

Force (kN)


(mm) Stress (Mpa)


89

While comparing the results from Tables 3.6-3.8, it can be seen that the connection

between frame and facade has only a minor effect on the seismic response of the

frame structure. In general the results showed that the incorporation of the VE

damping connections into the structure enabled moderate to significant reductions of

the various parameters of the structure that occurred during the earthquake.

3.15. Summary of finding

Based on the results following statements can be presented:

i. It is feasible to use energy absorbing connections in building facade

system to control facade deformation under seismic loads and minimise

facade failure.

ii. Connection properties have significant influence in the response and

have optimum values of stiffness kd = 20,000 kN/m and damping Cd =

35,000 kNs/m. There properties have been shown to be close to those

provided in the theory of Abbas and Kelly, 1993.

iii. The results from the proposed model calibrated well with existing

results and provided confidence.

iv. The application of selected earthquake records scaled to a PGA of 0.3g

had significant effects on the seismic response of building facade

system, as larger values in response for all investigated parameters

occurred compared to those under earthquake records scaled to a PGA

of 0.1g. However the energy absorbing connections were able to

control the deformation and forces in the connections, differential

displacement between frame and facade and the distortion of facades

reasonably well. bourn

v. The controlling criterion for this study was failure of the facades.

However the energy absorbing connections were also able to exert some

control on the overall structure as well.

vi. The seismic response of the building facade system, under the Kobe

earthquake, for the undamped structure was significantly higher in

values for all investigated parameters compared to the Northridge and


90

El Centro earthquakes. However considering the structure fitted with

the VE damping connections, the best result with the greatest reduction

in all investigated parameters were also achieved under the Kobe

earthquake excitations. The second highest reductions were obtained

under the El Centro earthquake. The reductions under the Northridge

earthquake were the lowest.

vii. In addition to controlling facade response, the energy absorbing

connections were able to exert some control on the overall structure as

well.

The use of energy absorbing connections (damping devices) to mitigate the seismic

simple three storey building facade system was first investigated in this study. The

results showed that the connection properties had significant influence on seismic

response of building facade system. The optimum values for spring stiffness and

dashpot damping were found as kd = 20,000 kN/m and Cd =35,000 kNs/m

respectively. The closer investigation of the three storey structure showed that the

effectiveness of the energy absorbing connectors varied under the different

earthquake records. This can be attributed to the varying intensity and frequency

content of the earthquake. The results of the study indicated that an increase in the

stiffness of spring did not have influence in controlling the behaviour of the facade.

However an increase in the dashpot damping value up to the optimum value has

shown to have an important role in reducing values in all parameters. Beyond this

value, the response of the seismic loading on the structure, started to increase. From

the several time history analyses carried out, it has been evident that with the

implementation of appropriate connection properties, the differential displacement

between the facade and the frame and the facade distortion can be considerably

reduced. Moreover the connection deformation and the connection forces can be kept

within reasonable and practical limits. Results have shown that the connection

stiffness and energy absorption capacity have a great influence in mitigating the

adverse effects of earthquakes. The feasibility of the computer analysis procedure

was established and the computer model was calibrated. The study has indicated the

possibility of developing connections with appropriate properties so as to minimise

facade failure during earthquakes.


91

This chapter concludes that it is feasible to design facade connection to minimize

their failure during seismic events. In the next chapter, the technique developed here

will be applied to 6, 12 and 18 storey buildings. The energy absorbing connections

can considerably reduce facade distortion and the differential displacement between

facade and frame, thus the energy absorbing connections have a favourable effect on

overall structure behaviour and are able to reduce inter-storey drifts.

After establishing the feasibility of the procedure, the efficiency of the VE damping

connections was investigated in three additional structural models, namely a 6-storey

building facade system model, a 12-storey building facade system model and an 18-

storey building facade system model which will be explained in the following

chapters.


92


93

Chapter 4

Analysis of 6-Storey Building Facade System


94

4. Analysis of 6-storey building facade system

4.1. Introduction

This chapter presents results from the finite element analysis of the second type of

structure - 6 storey 4-span building facade system. Undamped structure and structure

with VE damping connections with the varied properties and loads were considered.

The structure was analysed considering 2 separate load cases, as will be explained in

Section 4.2.1. These structures were analysed under the El Centro, Kobe and

Northridge earthquakes. In order to facilitate comparison of results all records were

scaled to PGA 0.1g to suit Australian conditions of lower seismic activity and to

facilitate comparison of results under the different seismic events. The results from

the finite element analysis of these structure in terms of the effect of the facades

mass, deformation of connections in terms of (extension/compression of spring),

axial forces in springs, differential displacement between facade and frame distortion

of facade and the interstorey drift are also presented in this chapter.

4.2. 6-storey building facade system

4.2.1. Description of 6-storey structural models

These structures have material and connection properties described in Sections (3.2

and 3.2.2). The facade panels were constructed from plane stress elements of the

same parameters in the previous models, and columns and beams with cross-

sectional dimensions increased to 0.4 x 0.4 m and 0.45 x 0.4 m, respectively. This

structure had four spans and the spans of the beams were 8.0 m and the height of the

storeys was 4.0 m, which gave an overall height of 24 m.

Energy absorbing connections were modelled with a spring and dashpot

(representing a VE damper). Both damped and undamped structures were analysed

under the above-mentioned (refer Section 4.1) earthquake excitations, considering

two load cases, to investigate the influence of load magnitude.

i. Load case 1: The vertical loading on the structure was in the form of

uniformly distributed loads of 75 kN/m applied to the lower storey

beams while the load distributed to the top storey beam was 50 kN/m.


95

ii. Load case 2: The vertical loading on the structure was in the form of

uniformly distributed loads of 40 kN/m applied to the lower storey

beams while the load distributed to the top storey beam was 34 kN/m.

Fig. 4.1 illustrates the model of the 6storey building –facade system.

Figure 4.1 Model of 6- storeys building facade system

The natural frequencies and periods of vibration of the 6 storey structure are

displayed in the following table.

Table 4.1 Natural frequencies a of 6-storey structure


Modes Natural

Frequency(Hz) Period of Vibration(T/Sec)

First 1.19 0.83 Second 3.69 0.27 Third 6.43 0.15

4.3. Seismic response of 6-storey structure for load case 1

There are various ways of assessing seismic response of the building facade system.

Computation of the deformation of connections in terms of (extension/compression

of spring), differential displacement between facade and frame, distortion of facade,

and interstorey drift provide meaningful effect of the earthquake on the building

facade systems.

The connections between the frame and facade in the undamped structure were

modelled as linear springs in the horizontal and vertical direction to replicate the

stiffness of the original connection. Spring stiffness was considered to have the value


96

of 20,000 kN/m for the horizontal connection and 35,000 kNs/m for the vertical

connection respectively as discussed before. The connections between the frame and

facade in the structure fitted with the VE damping connections were modelled by

springs and dashpots and were placed in the horizontal direction. Spring stiffness and

dashpot damping were considered to have the value of 20,000 kN/m and 35,000

kNs/m, respectively as discussed before. The vertical connections were modelled as

linear spring connections, with a stiffness of 35,000 kN/m. The seismic loading

applied to the structural system as mentioned previously, was horizontal, therefore

only the behaviour of the horizontal connections was considered. The model was

analysed under the El Centro, Kobe and Northridge earthquake excitations. Firstly,

the effect of the connection stiffness on the seismic response of the structural system

was investigated. Later on the building facade system was fitted with the VE

damping connections and was reanalysed to investigate the effectiveness of energy

absorber connection

Figures 4.2- 4.10 show the results of maximum responses of the undamped structure

and structure with the VE damping connections in terms of displacements between

frame and facade, interstorey drifts, deformations and forces in connections, as well

as distortion of facades (in the vertical and horizontal directions) obtained under the

El Centro, Kobe and Northridge earthquakes. Additional results can be found in

Appendix B. The reduction in the deformation of connections, forces in connections,

differential displacement between frame and facade, interstorey drifts and distortion

of facades in all storeys of the structure for the undamped structure and structure

with VE damping connections across the height of the structure (in panel 1) are

displayed in Figs. 4.2-4.6. In these figures UN and VE represent the undamped and

damped structures respectively. Herein x-axis refers to the story number which is

denoted by S. <number>; the “number” represents storey number (where n = 1 – 6).

In general, the results show that the second storey has the largest deformation and

forces in connections, differential displacement between frame and facade,

interstorey drifts and distortion of facade under all selected earthquakes. As it can be

observed in Fig. 4.2, the maximum deformation of connections under the El Centro

earthquake for an undamped structure was in ranged 1.03 – 4.47 mm. However, with

the introduction of VE damping connections to the structure, the deformation of


97

connections was reduced by an average of 80% across all storeys. In the case of the

Kobe earthquake, the deformations of connections were in range 1.25- 5.33 mm for

the undamped structure, while with the insertion of the VE damping connections, the

deformation of connections were reduced by an average of 84%.


0

1

2

3

4

5

6

7

8

S.2 S.3 S.4 S.5 S.6 S.2 S.3 S.4 S.5 S.6 S.2 S.3 S.4 S.5 S.6


De

fro

ma

tio

n (

mm

)

UN

VE

Figure 4.2 6-storey structure with and without VE damping connections, maximum

deformation of connections

The maximum deformation of connections under the Northridge earthquake was in

the range 1.37-7.15 mm. On the other hand, after the VE damping connections were

placed in the structure, the deformation of connections was reduced by an average of

81.55 %. The magnitudes of these improvements were of the same order as those of

others (Pinelli et al.)

As can be seen in Fig. 4.3, the greatest reduction in the axial forces in connections

was achieved under the Kobe earthquake. The maximum forces in connections under

the Kobe earthquake, for the undamped structure were in the range 25.01- 106.7 kN.

After the VE damping connections were placed in the structure an average reduction

of 84.11% was obtained across all storeys of the structure. This was followed by

reduction in the axial forces in the connections that occurred during the Northridge

earthquake. The maximum forces in connections under this earthquake, for

undamped structure were in the range 27.51 -143.1 kN. However, with the

introduction of VE damping connections, the forces in the connections were reduced

by an average of 81.56%.


98


0

30

60

90

120

150

180



Fo

rce

(kN

)UN

VE


force in connections

The reductions obtained under the El Centro earthquake were slightly lower, when

the maximum forces in connections for the undamped structure were in the range

20.83- 89.46 kN, whereas after the VE damping connections were fitted in the

structure, the forces in the connections decreased by an average of 80.41% across all

storeys. The overall results showed that the integration of the VE damping

connections to the building facade systems enhanced the reliability of the energy

absorption and decreased the seismic effect on the all level of the structure. However,

the performance of the VE damping connections in the upper levels provided better

mitigation of the forces than in the lower levels.

Very high efficiency of the damping connections was obtained also in terms of

reduction in differential displacement between frame and facade. As can be observed

in Fig. 4.4 the largest differential displacement between the frame and facade in the

undamped structure occurred under the Northridge earthquake excitation. A slightly

lower displacement was experienced under the Kobe earthquake. The differential

displacement that occurred under the El Centro earthquake was noticeably lower.

Fig. 4.4 illustrates that the maximum differential displacement between frame and

facades experienced under the El Centro earthquake for the undamped structure was

in the range 0.955 - 4.609 mm. However, with the introduction of the VE damping

connections, the differential displacement between the frame and facades were

reduced by an average of 79.43%.


99


0

1

2

3

4

5

6

7

8



Diff

ere

nti

al D

isp

lace

me

nt

(mm

)

UN

VE


differential displacement between frame and facade

The efficiency of the VE damping connections under the Kobe earthquake was even

higher, when the values of maximum differential displacement was in the range 0.76

- 5.57 mm for the undamped structure were reduced by an average of 82.7% for the

structure fitted with the VE damping connections.

The maximum differential displacement between frame and facade under the

Northridge earthquake, in the undamped structure was in the range 1.35–7.38 mm.

The greatest reduction in the peak values of differential displacement by an average

of 81.75% was achieved after the VE damping connections were placed in the

structure. The result showed that the incorporation of VE damping connections in

the building facade system improved the steadfastness of the energy absorption and

reduced the seismic effect on the all levels of the structure.

As can be seen in Fig. 4.5, the greatest interstorey drift occurred between the first

and second storey of the structure. The maximum interstorey drift under the El

Centro earthquake, for the undamped structure, was in the range 2.35 -23.17 mm.

However a considerable reduction with an average of 77.9% in the interstorey drift

was achieved during the same earthquake after the VE damping connections were

fitted in the structure. The interstorey drift under the Kobe and Northridge

earthquakes, for the undamped structure were in the range 2.04-27.74 mm and 3.38-

38.70 mm respectively.


100


05

10

15202530

354045

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7


Inte

rsto

rey

Dri

ft (

mm

)

UN

VE


interstorey drift

The structure fitted with the VE damping connections experienced even higher

reduction in the interstorey drift by an average of 81.78% for the Kobe and 80.66%

for the Northridge earthquakes respectively. The results showed that the structure

fitted with VE damping connections displayed an excellent performance under all

selected earthquakes. The reductions were usually increased towards the top storeys

and the range of the results was very close across all selected earthquakes.

The maximum reductions in the peak values of the distortion of facade experienced

by the undamped structure and the structure fitted with VE damping connections

under the El Centro, Kobe and Northridge earthquake are presented in Fig.4.6.

From the results it can be stated that the distortion of the facade under the El Centro

earthquake, for the undamped structure were in the range 0.000175-0.000353

Radian. However, a great reduction with an average of 79.22% in the distortion of

the facade was achieved across all storeys, when the structure was fitted with the VE

damping connections. The maximum distortions of facades experienced under the

Kobe earthquake for the undamped structures were in range 0.000182 - 0.000405

Radian. While after the VE damping connections were placed, the distortion of the

facade was reduced by an average of 82.7%. Similarly high efficiency was

experienced under the Northridge earthquake. The maximum distortion, of the facade

under this earthquake in the undamped structure were in the range from 0.000254 -

0.000554 Radian. With the placement of the VE damping connections in the

structure, the distortion of facades were reduced by an average of 81.75%.


101

Overall, the VE damping connections displayed extraordinary performance under all

selected earthquakes. In addition the efficiency of the VE damping connections in the

upper storeys provided better performance in terms of facade distortions.

The results indicated that so far in the majority of the cases the second storey

experienced the highest values in the response for all the investigated parameters. For

this reason, the behaviour of the structure under the seismic loading in the horizontal

direction of the structure was studied only in the second storey. The results also

showed that the middle spans of the second storey of the structure experienced the

largest values under all investigated parameters compare to the side spans under the

all selected earthquakes.


0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006



Dis

tort

ion

(Ra

dia

n)

UN

VE


distortion of facade

Fig. 4.7-4.10 demonstrates the reduction in response of the deformation in

connections, forces in connections, the differential displacement between frame and

facade and the distortion of facade under the El Centro, Kobe and Northridge

earthquakes in the second storey level across the width of the structure (horizontal

direction). In these Figures UN and VE represent the undamped and damped

structures respectively as mentioned before. Herein n.C-R represents “nth” column

right and n.C-L represent “nth” column left (where n = 1 – 5).

As can be observed in Fig. 4.7, the largest deformation in connections in the

undamped structure was obtained under the Northridge earthquake. The deformation


102

experienced under the Kobe earthquakes was slightly lower, while the lowest

deformation occurred under the El Centro earthquake.

The highest reductions in the deformation of connections were achieved under the

Kobe earthquake excitations when the maximum deformation for the undamped

structure 5.39 mm was reduced by 78.8%, when the VE damping connections were

fitted in the structure. The reduction obtained under the Northridge earthquake was

slightly lower. The maximum deformation of 7.25 mm for the undamped structure

was decreased by 75.77%, after the VE damping connections were introduced to the

building facade system.


0

12

3

45

6

78

9

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L


De

form

ati

on

(m

m)

UN

VE


deformation of connections

The lowest reduction in the deformation of connections was experienced under the El

Centro earthquake excitations. The deformation of connections experienced under

this earthquake for the undamped structure was 4.53 mm. However, when the VE

damping connections were fitted in the structure, the deformation of connection

decreased by up to 72.94%.

Fig. 4.8 demonstrates the effectiveness of the VE damping connections in terms of

axial forces under the El Centro, Kobe and Northridge earthquake excitations. The

results showed the same trend under the selected earthquakes for both the undamped

structure and the structure with VE damping connections.


103

Fig.4.8 illustrates that the best results with the greatest reductions were yet again

obtained under the Kobe earthquake. When the maximum forces of 107.91 kN in

connections for the undamped structure were reduced by 78.85%, with the insertion

of the VE damping connections to the structure. The maximum forces in the

connections under the Northridge earthquake, for the undamped structure were

145.25 kN. However, the incorporation of the VE damping connections in the

structure significantly reduced the forces in the connections by 75.80%.

The maximum forces in connections under the El Centro earthquake, for the

undamped structure were 90.83 kN, whereas, with the insertion of the VE damping

connections, the forces were reduced by up to 72.97%.


0

30

60

90

120

150

180

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L


Fo

rce

(kN

)

UN

VE


forces in connections

Fig. 4.9 illustrates the maximum reductions in the differential displacement between

frame and facade under the El Centro, Kobe and Northridge earthquake excitations.

As can be observed in Fig. 4.9, the maximum differential displacement between

facade and frame under the Northridge, Kobe and El Centro earthquakes, in the

undamped structure was 7.39 mm, 5.57 mm and 4.61 mm respectively. While with

the placement of the VE damping connections to the structure, the differential

displacement was reduced by 79.28% under the Kobe, 75.76% under the Northridge

and 72.24% under the El Centro earthquakes. In general, the results showed that the

reductions in differential displacement between frame and facade under the Kobe

earthquake were at a satisfactory high level. The reductions under the Northridge


104

earthquake were a little lower. The reductions under the El Centro were yet again the

lowest.


0123456789

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L

1.C

-R2

.C-L

2.C

-R3

.C-L

3.C

-R4

.C-L

4.C

-R5

.C-L


Diff

ere

nti

al D

isp

lace

me

nt (

mm

)

UN

VE

Figure 4.9 6 storey structure with and without VE damping connections, maximum

differential displacement between facade and frame

Fig.4.10 illustrates the reductions in the peak values of facade distortions obtained by

the 6-storey structure embedded with the VE damping connections compared with

that of the undamped structure. In contrast to the other investigated parameters, the

maximum distortion in facades was observed in the side spans.


0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p


Dis

tort

ion

(Ra

dia

n)

UN

VE




105

As regard to the undamped structure, the maximum distortion of facades under the

Northridge earthquake, for the undamped structure reached up to 0.000554 radian.

The maximum distortion of facades under the Kobe and El Centro earthquakes were

0.000405 radian and 0.000353 Radian respectively. The greatest results with

reductions of 79.49% in the distortion of facade were obtained under the Kobe

earthquake. This was followed by still significantly high reductions of 76.69%

recorded under the Northridge and 74.22% under the El Centro earthquake. In

general the results suggested that the VE damping connections operated effectively

under all selected earthquakes.


6-storey undamped structure and structure with VE damping connections as

discussed in Section 4.2.1 were considered. Uniformly distributed loads of 40 kN/m

were applied to the lower storey beams while a load distributed to the top storey

beam reduced to 34 kN/m as discussed earlier. These structures were analysed under

the El Centro, Kobe and Northridge earthquakes scaled to PGA of 0.1g.

Fig. 4.11-4.15 presents the results of maximum responses of the undamped structure

and structures with the VE damping connections in terms of displacements between

frame and facade, interstorey drifts, deformations and forces in connections, as well

as distortion of facades obtained under the El Centro, Kobe and Northridge

earthquakes. Additional results can be found in Appendix B. The largest

deformation of connections in the undamped structure occurred under the Northridge

earthquake excitation and only a slightly lower deformation was experienced under

the Kobe earthquake.

The deformation which occurred for the Northridge earthquake was lower. As it can

be seen from Fig. 4.11, the greatest reduction in the deformations of connections

occurred under the Kobe earthquake. The deformations of connections under this

earthquake were in the range from 1.64- 5.39 mm for the undamped structure. After

the VE damping connections were fitted in the structure the deformation was reduced

by an average of 75% across all storeys. The second highest reduction in the

deformation of connections occurred under the Northridge earthquake, when the

maximum deformation of connections for the undamped structure was in the range


106

from1.6– 5.5 mm. Whereas after the VE damping connections were inserted in the

structure, the deformation of connections was reduced by an average of 71.76%.


0

1

2

3

4

5

6



De

fro

ma

tio

n (

mm

)

UN

VE


deformations of connections

The reduction obtained under the El Centro earthquake was slightly lower. The

maximum deformation of 1.07-3.34 mm for the undamped structure decreased by an

average of 59.73% with the introduction of VE damping connections in the structure.

In these Figures UN and VE denote the results of the undamped and damped systems

respectively.

When the axial force experienced in the connections was evaluated (Fig. 4.12), the

best results were obtained under the Northridge earthquake excitation, where the

range of 32.8-110.05 kN obtained by undamped structure was reduced by an average

of 71.79% when the VE damping connections were fitted in the building facade

system. The efficiency of the VE damping connections under the Kobe earthquake

was noticeably more variable with the connection forces for undamped structure

32.89- 107.95 kN being reduced by an average of 75.08% when the structure was

fitted with VE damping connections. The lowest efficiency of the VE damping

connections was again experienced under the El Centro earthquake, where the range

of forces in connections was reduced from 21.45-66.8 kN by an average of 71.79 %

for the structure fitted with VE damping connections.


107


0

20

40

60

80

100

120



Fo

rce

(kN

)

UN

VE


force in connections

A very high efficiency of the damping connections was obtained also in terms of

reduction in differential displacement between frame and facade. From Fig. 4.13 it

can be observed that maximum differential displacement between frame and facades

experienced under the El Centro earthquake, for the undamped structure ranged from

0.59- 3.46 mm. However, with the introduction of the VE damping connections in

the structure, the differential displacement between the frame and facades was

reduced by an average of 73.86% across all storeys.

The efficiency of the VE damping connections was even higher under the Kobe

earthquake when the maximum differential displacement of 1.56- 5.63 mm for the

undamped structure was reduced by an average of 86.86%, after the VE damping

connections were fitted in the structure. The reduction under the Northridge

earthquake was adequately high when the maximum differential displacement

decreased by an average of 81%, with the introduction of the VE damping

connections to the structure.


108


0

1

2

3

4

5

6



Diff

ere

nti

al D

isp

lace

me

nt (

mm

)UN

VE


differential displacement between frame and facade

The results in terms of the interstorey drift of 6-storey structure are presented in Fig.

4.14. The maximum interstorey drift occurred between the first and second storey of

the structure. In relative terms, the best performance of the damping connections was

obtained under the Kobe earthquake, where the interstorey drift were in the range

3.59- 27.99 mm for the undamped structures, was reduced by an average of 86% for

the structures equipped with the VE damping connections.

A slightly lower reduction in the interstorey drift was achieved under the Northridge

earthquake. The maximum interstorey drift under this earthquake for the undamped

structure were in the range 3.22- 29.06 mm. However, with the introduction of the

VE damping connection to the structure, the interstorey drift was reduced by an

average of 80.40% across all storeys. The maximum interstorey drift under the El

Centro earthquake, for the undamped structure, were in the range 1.45-18.12 mm.

Whilst after the VE damping connections were placed in the structure, the interstorey

drift was reduced by an average of 74%. As can be seen from these results, under all

three selected earthquake excitations, a reduction in interstorey drift usually

increased towards the uppermost storeys. In general however, the VE damping

connections functioned perfectly well in all storeys and the range of the results across

all three earthquakes was very close.


109


0

5

10

15

20

25

30

S1

-2S

2-3

S3

-4S

4-5

S5

-6S

6-7

S1

-2S

2-3

S3

-4S

4-5

S5

-6S

6-7

S1

-2S

2-3

S3

-4S

4-5

S5

-6S

6-7


Inte

rsto

rey

Dri

ft (

mm

)

UN

VE


interstorey drift

The results in terms of the maximum distortion of the facade are illustrated in Fig.

4.15 The distortion of facade under the El Centro, Kobe and Northridge earthquakes,

for the undamped structure were in the range 0.000113 - 0.00025 Radian, 0.00024-

0.00042 Radian and 0.000223 -0.00042 Radian respectively. However, with the

introduction of the VE damping connections to the structure, the distortion of facade

was reduced by an average of 75.23, 85.92 and 81.11% respectively


00.000050.0001

0.000150.0002

0.000250.0003

0.000350.0004

0.00045



Dis

tort

ion

(R

ad

ian

)

UN

VE


distortion of façade


110

The efficiency of the VE damping connections in terms of the distortion of facade

was significantly high across all storeys under the selected earthquakes.

4.5. Seismic response of 6-storey building facade system for load case 2: -effects of facade mass (undamped structure)

A six storey building structure with the properties and loads as described in section

4.2.1 was considered. The main purpose of this investigation was to study the effect

of the facade mass. A façade material was selected and its thickness was varied to

give different masses and the behaviour of the building facade system was observed.

Thus, precast concrete facade panels were selected and modelled, with a thickness of

180, 150 and 100 mm. The structure with facade panels of 180 mm thick represented

22% of the total structural mass. The structure with facade panels of 150 mm thick

represented 19% of overall mass of the building structure and finally, the structure

fitted with facades having thickness of 100 mm, represented 13.5% of the overall

structural mass.

Stiffness parameters of 35,000 kN/m and 20,000 kN/m were determined for the

vertical and horizontal connections respectively. The structure was subjected to the

El Centro, Kobe and Northridge earthquake excitations scaled to PGA of 0.1g, and

was analysed considering load case 2. The response of the structure was obtained for

selected time steps of the input earthquakes accelerogram. The maximum

deformation and axial force in connections, the differential displacement between

facade and frame, the distortion of the facade and the interstorey drift were the key

parameters and they are shown in Fig 4.16-4.20. Additional results can be found in

Appendix B.

The result of the investigated parameters for the structure with facade panels of 180

mm was compared with that of the structure with the thickness of 150 mm and 100

mm. As can be observed in Fig.4.16, the deformation of the connection under

Northridge earthquake, was in the range of 1.69-5.73 mm, 1.64-5.5 mm and 1.53-

5.07 mm for the structure fitted with a facade panel of thickness 180 mm, 150 mm

and 100 mm respectively. The deformation of connections under the Kobe

earthquake, varied in range from 1.68-5.48 mm, 1.64-5.39 mm and 1.59-5.25 mm for

the structure fitted with facade panels of thickness 180 mm, 150 mm and 100 mm

respectively. Under the El Centro earthquake, the deformation were in the range


111

1.14-3.51 mm, 1.07-3.34 mm and 0.93-3.01mm for the structures fitted with facade

panels of thickness 180 mm, 150 mm and 100 mm respectively.


01234567



Building Storey

De

form

ati

on

(m

m)

180 150 100


deformations in connections

As can be seen from these results, the deformation in connections under all three

selected earthquakes, regularly decreased towards the uppermost storeys, however

the range of the results was very close across all selected earthquakes.

The results of the axial forces in the connections are presented in Fig 4.17. The axial

forces in the connections which occurred under the Northridge earthquake were in

the range from 33.91-114.7 kN, for facades with thicknesses of 180 mm, 32.8-110.05

kN for facades with thickness of 150 mm and 30.73-101.52 kN, and for facades with

thickness of 100 mm.

In the case of the Kobe earthquake, the axial forces in the connections were in the

range 33.78-109.67 kN for facades with a thickness of 180 mm, 32.89-107.95 kN

and 31.92-105.16 kN and for facades with a thickness of 150 mm and 100 mm

respectively. The axial force in connections, under the El Centro earthquake were in

the range from 22.98-70.32 kN for facades with a thickness of 180 mm, 21.45-66.8

kN for facades with thickness of 150 mm and 18.64-60.2 kN for facades with a

thickness of 100 mm correspondingly.


112


020406080

100120140



Building Storey

Fo

rce

(kN

)

180 150 100


forces in connections

As it can be seen from Fig. 4.18, the highest interstorey drifts occurred under the

Northridge earthquake where in the case of the structure fitted with a facade of

thickness 180 mm range the interstorey drift was 3.27-30.139 mm; in the structure

fitted with facade panels of thickness 150 and 100 mm range the interstorey drift was

3.22-29.06 mm and 3.16-27.15 mm respectively.

The interstorey drift under the Kobe earthquake, were in the range from 2.82-27.92

mm for structure with facades of thickness 180 mm, 3.59-27.99 mm and 3.65-

26.54mm for structure with facades of thicknesses of 150 mm and 100 mm

respectively.

The inter-storey drift under the El Centro earthquake was in the range 1.67-19.1 mm,

for structure with facades of thickness 180 mm. It ranged from 1.45-18.12 mm and

1.2-16.39 mm for a structure with facades of thicknesses 150 mm and 100 mm

respectively.


113


05

101520253035

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7

S1

-2

S2

-3

S3

-4

S4

-5

S5

-6

S6

-7


Building Storey

Inte

rsto

rey

Dri

ft (m

m)

180 150 100


interstorey drifts

Fig 4.19 shows the results in terms of differential displacement between frame and

facade. As it can be seen in this Fig., the differential displacement under the El

Centro earthquake was in range 0.73-3.64 mm, 0.59-3.46 and 0.49-3.14 mm, for

facades with thicknesses of 180 mm, 150 mm and 100 mm respectively.

6-Storey Concrete Fram

01234567



Building Storey

Diff

ere

nti

al D

isp

lace

me

nt (

mm

)

180 150 100



The differential displacement between frame and facades under the Kobe earthquake

excitations, varied in range 1.23-5.72 mm, 1.56-5.63 mm and 1.52-5.39 mm, for the

structures with facades of thickness of 180 mm, 150 mm and 100 mm respectively.

In the case of the Northridge earthquake, differential displacement ranged from 1.45-


114

5.97 mm, 1.39-5.74 mm and 1.29-5.13 mm, for the structure fitted with facades of

thickness of 180 mm 150 mm and 100 mm respectively.

As it can be seen from Fig. 4.20, the distortion of the facade under the El Centro

earthquake was in the range 0.00012-0.00025 radian, 0.00011-0.00025 Radian and

0.000092-0.00023 radian for the structure fitted with facades of thicknesses 180 mm,

150 mm and 100 mm respectively.

The distortion of the facade under the Kobe earthquake, varied in range from

0.00020-0.00043 radian, 0.00024 -0.00042 radian and 0.00024-0.00042 radian for

the structure fitted with facades of thicknesses 180 mm, 150 mm and 100 mm

respectively. In the case of the Northridge earthquake, the distortion of facade

ranged from 0.00022-0.00044 radian, 0.00022-0.00042 radian and 0.00021-0.00039

radian, for facades with thicknesses of 150 mm, 180 mm and 100 mm respectively.


0

0.0001

0.0002

0.0003

0.0004

0.0005



Building Storey

Dis

tort

ion

(Ra

dia

n)

180 150 100



From Fig 4.16-4.20, it can be observed that the mass of the facade had a very little

effect on the deformation and axial force in connections, differential displacement

between facade and frame, the distortion of the facade and interstorey drifts.


115

4.6. Summary of findings

The results from the 6-storey building facade system with and without VE damping

connections considering 2 separate load cases 1 and 2, under the El Centro, Kobe and

Northridge earthquakes were investigated. The results from the undamped structures

revealed high levels of the deformation and axial forces in connections, differential

displacement between facade and frame, distortion of facade, and interstorey drift

under the selected earthquake excitations. The largest values for all the investigated

parameters under the load case 1 (larger load), was experienced under the Northridge

earthquake. It was followed by the significantly high values obtained under the Kobe

earthquake. The values obtained under the El Centro earthquake were the lowest.

Considering load case 2 (smaller load), similarly the largest values for all the

investigated parameters were experienced under the Northridge earthquake. The

values obtained under the Kobe earthquakes were very close to those of the

Northridge. The El Centro earthquake yet again produced the lowest values for all

the investigated parameters.

The overall results showed that the integration of the VE damping connections to the

building facade systems enhanced the reliability of the energy absorption and

decreased the seismic effect on facade at the all levels of the structure. However, the

performance of the VE damping connections in the upper levels provided better

seismic mitigation than in the lower levels. Reduction in all investigated parameters

usually increased towards the uppermost storeys under all three earthquake

excitations.

Considering load cases 1 and 2, the results showed that the greatest average

reduction in deformation and forces in connections, differential displacement

between facade and frame, and the distortion of facade was experienced under the

Kobe earthquake excitation, which was characterised by a strongly narrow dominant

frequency range (0.29-1.12 Hz). The second highest average deflection reduction

occurred under the Northridge earthquake, which had a strongly dominant narrow

frequency range (0.14-1.07 Hz). In the case of the El Centro earthquake excitation,

which exhibit a wide band of dominant frequencies (0.39-6.39Hz), the efficiency of

the VE damping connections was slightly lower, probably because the natural

frequency of the structure was within this band of earthquake dominant frequencies.


116

Under load case 1 (larger load), structure provided higher reductions in all

investigated parameters in comparison to those obtained under load case 2 (smaller

load). However, the energy absorbing connections in building facade system were

able to control facade distortion reasonably well considering both load cases under

the chosen earthquake excitations.

The results of deformation and axial forces in connections, differential displacement

between frame and facade and distortion of the facade under the El Centro, Kobe and

Northridge earthquake excitations in the second storey level across the width of the

structure (horizontal direction) were very close.

Increase in the facade mass under the Kobe earthquake, gave a complex response on

the deformation of connections, distortion of facade, differential displacement

between frame and facade and interstorey drift. However, under the El Centro and

Northridge earthquake excitations, an increase in the facade mass displayed a very

little effect in the all investigated parameters.

Overall, the connections properties developed in this research are able to have

favourable results even when the natural frequencies of the structure are within the

dominant frequencies of the earthquakes.


117

Chapter 5



118


5.1. Introduction

This chapter presents results from the finite element analysis of the third type of

structure - 12 storey building facade system. Damped and undamped structures fitted

with precast concrete and glass facades were considered. These structures were

analysed considering 2 load cases. The structures fitted with precast concrete

facades, were analysed under the El Centro, Kobe and Northridge earthquakes scaled

to PGA 0.2g, while the structures with glass facades were analysed only under the El

Centro earthquake scaled to PGA 0.1g. As mentioned earlier, the 12-storey models

have natural frequencies within the range of the dominant modes of this earthquake

and hence this study also included resonant conditions.





Modes Natural

Frequency(Hz) Period of

Vibration(T/Sec) First 0.84 1.17

Second 2.58 0.38 Third 4.44 0.22

5.2. Seismic response of 12-storey building facade system with precast concrete facade for load case 1

The facade panels of the twelve-storey building facade system, as described in

section 3.2 were modelled using two-dimensional plane stress elements. The

dimensions of the facade panels were 7.9 m wide, 3.9 m high and 0.15 m thick. The

connections between the frame and facade in the undamped structure as mentioned

earlier were modelled by springs, in order to replicate the stiffness of the original

connections. The horizontal connection had a spring stiffness of 20,000 kN/m and

the vertical connections had a spring stiffness of 35,000 kNs/m as discussed before.

Energy absorbing connections were modelled by springs and dashpots, (in the

horizontal direction). Spring stiffness and dashpot damping were considered to have


119

the values of kd = 20,000 kN/m and Cd = 35,000 kNs/m, respectively as discussed

before. The vertical connections were modelled as spring connections having a

stiffness of 35,000 kN/m. The results in terms of differential displacements between

frame and facade, deformations and forces in connections, distortion of facades as

well as interstorey drifts in all storeys of the structure for the undamped structure and

structure with VE damping connections across the height of the structure (in panel 1)

are presented in Figures 5.1 - 5.5. Additional results can be found in Appendix C.

Herein x-axis refers to the story number which is denoted by S. <number>; the

“number” represents storey number (where n = 1 – 12). Moreover, UN and VE

represent the undamped and damped structures respectively.

In the case of the El Centro earthquake, the undamped structure experienced

deformations in connection (Fig. 5.1) varying in the range 1.59-12.58 mm. On the

other hand, with the introduction of VE damping connections in the building facade

system, the deformation of connection for investigated parameters was reduced by an

average of 83%. Similarly, under the Kobe earthquake the undamped structure

experienced deformation in connections in the range 2.45-6.23 mm, whereas when

VE damping connections were used, the deformations in the connections were

reduced by an average of 79.59%. The lowest deformation reductions were

experienced under the Northridge earthquake, where the range of deformation was in

range 1.63 -12.4 mm for the undamped structure and was reduced by an average of

78.32% when the connecting VE damping connections were installed.

When the force experienced in the connections was evaluated (Fig. 5.2), the best

results were obtained under the El Centro earthquake excitation, where the range of

31.92-251.65 kN obtained by the undamped structure was reduced by an average of

83%. When the VE damping connections were fitted in the building facade system.


120


0

2

4

6

8

10

12

14

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


De

form

ati

on

(m

m)

UN

VE

Figure 5.1 12-storey structure with and without VE damping connections, maximum deformations in connection.

The efficiency of the VE damping connections under the Kobe earthquake was

slightly lower when the connection forces for the undamped structure (92.2-124.7

kN) was reduced by an average of 79.6%, after the structure was fitted with VE

damping connections. The lowest efficiency of the VE damping connections was

again experienced under the Northridge earthquake, where the range of forces in the

connections was reduced in the range 32.72 -248.12 kN by an average of 78.25%, for

the structure fitted with VE damping connections.


0

50

100

150

200

250

300

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Fo

rce

(kN

)

UN

VE

Figure 5.2 12 - storey structure with and without VE damping connections, maximum forces in connection


121

Fig. 5.3 shows the results in terms of the differential displacement between facade

and frame. As can be seen in this figure, differential displacement under the El

Centro earthquake for the undamped structure was in the range 1.56-12.92 mm. In

comparison, when the building facade system was fitted with the VE damping

connections the differential displacement was decreased by an average of 80.83%.

Slightly lower reductions in differential displacements were experienced under the

Northridge earthquake, where the differential displacement between the frame and

facade for the undamped structure of values 1.25-12.32 mm was reduced by an

average of 79.38% when VE damping connections were used. In the case of the

Kobe earthquake excitations the undamped structure experienced differential

displacement in the range 1.61-6.1 mm, whereas with the introduction of VE

damping connections to the building facade system, the differential displacement

decreased by an average of 75.95%.


0

2

4

6

8

10

12

14

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Diff

ere

nti

al D

isp

lace

me

nt(

mm

)

UN

VE

Figure 5.3 12-storey structure with and without VE damping connections, maximum differential displacements

The results in terms of the interstorey drift of 12-storey drift are presented in Fig. 5.4.

The highest performance of the VE damping connections was obtained under the El

Centro earthquake excitations, where the interstorey drift ranged from 5.86 mm to

29.41 mm for the undamped structures was reduced by an average of 79.8% for the

structures equipped with VE damping connections.


122

12-Story Concrete Frame

0

5

10

15

20

25

30

35

S1

-2S

2-3

S3

-4S

4-5

S-5

-6S

6-7

S7

-8S

8-9

S9-

10

S1

0-1

1S

11-

12

S1

2-1

3S

1-2

S2

-3S

3-4

S4

-5S

-5-6

S6

-7S

7-8

S8

-9S

9-1

0S

10-

11

S1

1-1

2S

12-

13

S1

-2S

2-3

S3

-4S

4-5

S-5

-6S

6-7

S7

-8S

8-9

S9-

10

S1

0-1

1S

11-

12

S1

2-1

3


Inte

rsto

rey

Dri

ft (

mm

)

UN

VE

Figure 5.4 12-storey structure with and without VE damping connections, maximum interstorey drift

Slightly lower performance of the connecting VE damping connections occurred

under the Northridge earthquake, where the interstorey drift for the undamped

structures in the range 5.4-28.75 mm were reduced by an average of 77.46% when

VE damping connections were used. In general, it can be stated that VE damping

connections obtained significant results in all storeys and under all excitations. The

range of the results for the Kobe earthquake was noticeably more open when the

interstorey drift for the undamped structures, in range 5.26-15.37 mm, was reduced

by an average of 75.08 % for the structure equipped with VE damping connections.

VE damping connections also have a dramatic influence on the distortion in the

facade (Fig. 5.5). Under the El Centro and Kobe earthquake excitations undamped

structures experience facade distortions of range 0.000777- 0.001134 and 0.000233 -

0.000871 radian, respectively, with the introduction of VE damping connections

causing an average reduction of 79.27 and 70.47%. A similar effect was observed

under the Northridge earthquake excitation with the distortion in facade experienced

by the undamped structure (0.000979- 0.001232 radian) being reduced by an average

of 77.35% by the presence of VE damping connections.


123


0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Dis

tort

ion

(R

ad

ian

)

UN

VE

Figure 5.5 12- storey structure with and without VE damping connections, maximum distortion of façade.

Figures 5.6-5.9 illustrate the maximum responses of the structure in terms of

displacements between frame and facade, deformations and forces in connections,

distortion of facades as well as interstorey drifts in the second storey level across the

width of the structure (horizontal direction) under all three earthquakes. In these

Figures UN and VE represent the undamped and damped structures respectively as

mentioned before. Additional results can be found in Appendix C. Herein n.C-R

represents “nth” column right and n.C-L represent “nth” column left (where n = 1 –

5).

It can be clearly observed in Fig. 5.6 that the deformation in connection experienced

by the undamped structure under the El Centro earthquake (12.48-12.84 mm), was

reduced by an average of 77.9% by the presence of damping in the connections.

Under the Northridge earthquake conditions a slightly lower decrease in deformation

in connections was observed with the deformations between 12.3-12.73 mm in the

undamped structure being reduced by an average of 67.31%. The deformation under

the Kobe earthquake varied in range from 6.18-6.24 mm for the undamped structure

and this was reduced with the introduction of VE damping connections in the

building facade system by an average of 60. 8%.


124


0

2

4

6

8

10

12

14

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L


De

form

atio

n (

mm

)

UN

VE

Figure 5.6 12-storey structure with and without VE damping connections, maximum deformation in connections

Fig. 5.7 presents the decrease in force in connection that result from the presence of

VE damping connections. The results showed that the axial forces in connections

experienced under the El Centro, Kobe and Northridge earthquakes excitations for

the undamped structure were in the range 249.69-257.19 kN, 123.67-124.97 kN and

246.25-254.89 kN, respectively. Once again, the 12 storey structure showed

significant decreases in this parameter under the El Centro, Kobe and Northridge

earthquakes when the VE damping connections were introduced. These average

reductions were in the ranges by 77.9%, 60. 80% and 67.31% respectively.


0

50

100

150

200

250

300

1.C

-R2.C

-L2.C

-R3.C

-L3.C

-R4.C

-L4.C

-R5.C

-L

1.C

-R2.C

-L2.C

-R3.C

-L3.C

-R4.C

-L4.C

-R5.C

-L

1.C

-R2.C

-L2.C

-R3.C

-L3.C

-R4.C

-L4.C

-R5.C

-L


Fo

rcr (k

N)

UN

VE

Figure 5.7 12-storey structure with and without VE damping connections, maximum force in connection


125

The data in Fig. 5.8 demonstrates the differential displacement between frame and

facade experienced, under the El Centro earthquake. Values for the undamped

structure varied in the range from 12.75-13.12 mm, however by the introduction of

VE damping connections in the building facade system, were decreased by an

average of 87.82%.

The differential displacement between frame and facade experienced under the Kobe

earthquake for the undamped structure ranged from 6.3-6.4 mm, while, with the

introduction of viscoelastic damping connections in the building facade system, the

deformation of connection decreased by an average of 60.69%. The differential

displacement between frame and facade under the Northridge earthquake, for

undamped structure were in the range 12.14-12.57 mm, however, with the

introduction of VE damping connection in the building facade system, the

differential displacement decreased by an average of 66.29%.


0

2

4

6

8

10

12

14

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L


Diff

ere

nti

al D

isp

lace

me

nt

(mm

)

UN

VE

Figure 5.8 12-storey structure with and without VE damping connections, maximum differential displacement between facade and frame.

The distortion in the facade experienced by the 12 storey structure was also greatly

reduced by VE damping connections and this is demonstrated in Fig. 5.9.


126


0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p


Dis

tort

ion

(Ra

dia

n)

UN

VE

Figure 5.9 12-storey structure with and without VE damping connections, maximum distortion of façade.

Under the El Centro earthquake the undamped structure showed distortions in the

facade varying in the range from 0.00089 - 0.001054 radian. The distortion in the

facade experienced under the Kobe and Northridge earthquakes, for the undamped

structure varied in range from 0.000413 -0.000432 Radian and 0.000895 - 0.00108

Radian, respectively. The introduction of VE damping connections in the building

facade system resulted in an average reduction of 77.95% in this distortion under the

El Centro earthquake. Similar reductions in distortion in the facade were also

observed under the Kobe and Northridge earthquake conditions with an average

value of 58.2 % and 69.20% respectively.

5.3. Seismic responses of 12-storey building facade system for load case 2


discussed in Section 3.2 and 3.2.2 were considered. The connections with the same

properties as discussed in Sec. 5.3.1 were chosen. Uniformly distributed loads of 40

kN/m were applied to the lower storey beams while a load distributed to the top

storey beam reduced to 34 kN/m as discussed earlier. These structures were analysed

under the El Centro, Kobe and Northridge earthquakes scaled to PGA of 0.2g.


127

Figs. 5.10 - 5.12 display the typical time history responses of the deformation of

connections, the differential displacement between frame and facade, and the

distortion of facade for the 12-storey undamped structure and structure with VE

damping connections at second storey.

12-Storey Building Facade System

-8-6-4-202468

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (Sec)

De

form

ati

on

(mm

)

UN

VE

Figure 5.10 12-storey structure with and without VE damping connections, time histories of deformation in upper and lower connection of facade

As can be seen from Fig 5.10, the maximum deformation of connection under the El

Centro earthquake excitation, for the undamped structure was limited to a short time

interval of about 6.3 seconds with a magnitude of 5.99mm. However, the

incorporation of the VE damping connections to the structure resulted in significant

reduction in the deformation of connections at the time interval of about 2.94

seconds by up to 67.4 %. In these Figures UN and VE denote the results of the

undamped and damped systems respectively.

As can be observed from Fig 5.11, the maximum differential displacement between

frame and facade under the El Centro earthquake excitation, for the undamped

structure was limited to a short time interval of about 6.3 seconds with a magnitude

of 6.16 mm. While the integration of the VE damping connection to the structure

resulted in considerable decrease in the differential displacement at the time interval

of about 2.94 seconds by up to 67.37 %.


128


-8-6-4-202468

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Time (Sec)

Diff

ere

nti

al

Dis

pla

cem

en

t (m

m)

UN

VE

Figure 5.11 12-storey structure with and without VE damping connections, time histories of differential displacement between frame and façade.

Similarly, Fig 5.12 shows that the distortion of facade under the El Centro

earthquake excitation, for the undamped structure was limited to a time interval of

about 6.3 seconds with a magnitude of 0.00050 radian. However, the inclusion of the

VE damping connection to the structure resulted in significant reduction in the

distortion of facade at the time interval of about 2.94 seconds by up to 67.6 %.


-0.0006-0.0005-0.0004-0.0003-0.0002-0.0001

00.00010.00020.00030.00040.00050.0006

0 1 2 3 4 5 6 7 8 9 10

Time (Sec)

Dis

tort

ion

(R

ad

ian

)

UN

VE

Figure 5.12 12-storey structure with and without VE damping connections, time histories of distortion of façade.


129

Figures 5.13 – 5.17 illustrates the maximum responses in terms of displacements

between frame and facade, deformations and forces in connections, interstorey drifts,

as well as distortion of facades under El Centro, Kobe and Northridge earthquakes.

Additional results can be found in Appendix C.

As can be seen from Fig. 5.13, the maximum deformation of connections under the

El Centro earthquake for the undamped structure, ranged from 1.79-5.99 mm.

However, with the introduction of VE damping connections in the building facade

system, the deformation of connections was reduced by an average of 68.8%.

The maximum deformation of connections under the Kobe earthquake, for the

undamped structure varied in range 2.27- 6.81 mm. While with the introduction of

the VE damping connections in the structure the deformation of connections was

reduced by an average of 73.61%. The maximum deformation of connections under

the Northridge earthquake, for the undamped structure ranged from 1.71–9.75 mm.

However, with the introduction of the VE damping connection in the structure the

deformation of the connection decreased by an average of 71.32%


0123456789

10

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

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De

form

ati

on

(m

m)

UN

VE

Figure 5.13 12-storey structure with and without VE damping connections, maximum deformations in connection

As it can be seen from Fig. 5.14, the maximum forces in the connections under the El

Centro earthquake in the undamped structure were in range 35.92 -119.96 kN. The

highest value of 119.96 kN occurred at 2nd storey, then decreased towards the5th

storey, and increased towards to 7th storey and then began to decrease toward the


130

top. Whereas, with the introduction of the VE damping in the structure the forces in

connections reduced by an average of 68.8%.


020406080

100120140160180200

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

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2


Fo

rce

(kN

)

UN

VE

Figure 5.14 12-storey structure with and without VE damping connections, maximum forces in connection

The maximum forces in connections under the Kobe earthquake, for undamped

structures varied in a range 45.42 - 136.32 kN with the highest value of 136.32 kN at

the 2nd storey, then decreasing up to 4th storey, then up to 7th storey were increasing

and decreasing up to the top. However, with the introduction of VE damping

connections in the structure, the forces in connections were decreased by an average

of 73.6%. The maximum forces in connections under the Northridge earthquake, in

the undamped structure were in range 34.33 -195.19 kN with the highest value of

195.19 kN at 2nd storey and were decreasing toward the top. While, with the

introduction of VE damping connections in the structure, the forces in the

connections decreased by an average of 70.04%.

As it can be seen from Fig. 5.15, the maximum differential displacement between the

frame and facade under the El Centro earthquake for the undamped structure were in

range 1.4 - 6.16 mm with the highest value of 6.16 mm at 2nd storey, then decreasing

up to the 6th storey, then increasing up to the 9th storey and then decreasing toward

the top. However, with the introduction of VE damping connections to the structure,

the differential displacement between the frame and facade was reduced by an

average of 78.17%.


131

The differential displacement between the frame and facade under the Kobe

earthquake, for the undamped structure, was in range 1.91- 6.99 mm with the highest

value of 6.99 mm at 2nd storey, then decreasing up to 6th storey, and then once again

in 7th storey it increased rapidly and then decreased up to the top. On the other hand,

with the introduction of VE damping connections to the building facade system, the

differential displacement between the frame and facade was reduced by an average

of 81.14%.

The maximum differential displacement between the frame and facade under the

Northridge earthquake, for the undamped structure, ranged from 1.11 – 10.02 mm

with the highest value of 10.2 mm at 2nd storey decreasing up to the top. However,

with the insertion of the VE damping connections in the structure the differential

displacement between the frame and facade was reduced by an average of 80.27%.


-1

1

3

5

7

9

11

S.2

S.3

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S.5

S.6

S.7

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.3S

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.5S

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.10

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S.1

0S

.11

S.1

2


Diff

ere

nti

al D

isp

lace

me

nt(

mm

)

UN

VE

Figure 5.15 12-storey structure with and without VE damping connections, maximum differential displacement

As can be seen form Fig. 5.16, the maximum interstorey drifts under the El Centro

earthquake, in the undamped structure was in range 7.75-14.05 mm with the highest

value of 14.05 mm at 2nd storey decreasing up to the 6th storey, then increasing up

to the 10th storey and then decreasing up to the top. However, with the introduction

of the VE damping connection to the structure, the interstorey drifts decreased by an

average of 76.18 %.


132

The maximum interstorey drifts under the Kobe earthquake, for the undamped

structure, were in the range 9.15- 16.05 mm with highest value of 16.05 mm at the

2nd storey decreasing up to 6th storey, then increasing up to 8th storey and then

decreasing up to the top. However, with the insertion of VE damping connections in

the structure, the maximum interstorey drifts were reduced by an average of 80.08%.

The interstorey drift under the Northridge earthquake, for the undamped structure,

were in range 7.04- 22.86 mm with the highest value of 22.86 mm at the 3rd storey

and then were decreased toward the top. On the other hand, with the introduction of

VE damping connection to the structure, the interstorey drifts were reduced by an

average of 78.6%.


0

5

10

15

20

25

S1

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10

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S3

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2-3

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11-

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Inte

rsto

rey

Dri

ft (m

m)

UN

VE


As can be seen form Fig. 5.17, the maximum distortion of facade under the El Centro

earthquake, for the undamped structure was in range 0.00048 - 0.00081 radian.

However, with the introduction of VE damping connection to the structure, the

distortion of facade reduced by an average of 76.36%.


133

12 Storey Concrete Frame

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

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.11

S.1

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S.8

S.9

S.1

0S

.11

S.1

2


Dis

tort

ion

(R

ad

ian

)

UN

VE

Figure 5.17 12-storey structure with and without VE damping connections, maximum distortion of façade

The maximum distortion of facades under the Kobe earthquake, for the undamped

structure was in range 0.000418 - 0.000857 radian. However, with the introduction

of VE damping connections to the structure, the distortion of facades was reduced by

an average of 80.92%. The maximum distortion of the facade under the Northridge

earthquake, for the undamped structure was in range 0.00068 - 0.00101 radian. On

the other hand, with the insertion of VE damping connections in the structure, the

distortion of facades was reduced by an average of 79.40%.

From Figures 5.13 - 5.17 the seismic responses of building facade system associated

with maximum force in connections, deformation in connection, differential

displacement, interstorey drift, distortion, differential displacement, displayed similar

trends. All responses for building facade system with VE damping connections

produced significantly better results than building facade system without VE

damping connections. The structures fitted with VE damping connections exhibited

significantly high improvement in all investigated parameters under the El Centro

Kobe and Northridge earthquakes.

5.4. Seismic responses of 12-storey undamped structure and structure with VE connections under higher seismic loads

The same 12-storey building facade systems with the parameters, material properties

and loads as described in Section 5.4 was also analysed under the El Centro, Kobe

and Northridge earthquake records, however this time scaled to PGA of 0.5g.


134

Uniformly distributed loads of 40 kN/m were applied to the lower storey beams,

while a load distributed to the top storey beam was reduced to 34 kN/m (load case 2).

Results are presented in the following sections where the values within brackets

denote results for PGA 0.2g.

Figures 5.18 – 5.22 illustrates the maximum responses in terms of displacements


as well as distortion of facades under El Centro, Kobe and Northridge earthquakes.

Additional results can be found in Appendix C.

In these Figures UN and VE denote the results of the undamped and damped systems

respectively. As can be seen from Fig. 5.19, the maximum deformation of

connections under El Centro earthquake for the undamped structure, were in range

3.89-14.98 mm (1.79-5.99 mm). However, with the introduction of VE damping

connections in the building facade system, the deformation of connections was

reduced by an average of 76.85% (68.8%). The maximum deformations of

connections under the Kobe earthquake, for the undamped structure were in range

5.22- 17.03 mm (2.27- 6.81 mm). While with the introduction of the VE damping

connections in the structure the deformation of connections were reduced by an

average of 80.67% (73.61%). The maximum deformations of connections under the

Northridge earthquake, for the undamped structure were in range 3.66-24.39 mm

(1.71–9.75 mm). However, with the introduction of the VE damping connection in

the structure the deformation of the connection were decreased by an average of 77%

(71.32%).


135

12-Storey Building Façade System

02468

101214161820222426

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

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S.5

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S.8

S.9

S.1

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.11

S.1

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De

form

ati

on

(m

m)

UN

VE

a) Maximum deformations in connection, results under 0.5g


0123456789

10

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


De

form

ati

on

(m

m)

UN

VE

b) Maximum deformations in connection results under 0.2g

Figure 5.18 12-storey structure with and without VE damping connection, maximum deformations

As it can be seen from Fig. 5.19, the maximum forces in the connections under the El

Centro earthquake for the undamped structure were in range 77.93-299.69 kN (35.92

-119.96 kN) with highest value of 299.69 kN (119. 96 kN) at 2nd storey then values

decreased up to the5th storey, then increased further up to 7th storey and once again

began to decrease toward the top. Whereas, with the introduction of the VE damping

in the structure the forces in connections were reduced by an average of 76.87%

(68.8%).


136


050

100150200250300350400450500

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Fo

rce

(kN

)UN

VE

a) Maximum forces in connection, results under 0.5g


020406080

100120140160180200

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Fo

rce

(kN

)

UN

VE

b) Maximum forces in connection, results under 0.2g

Figure 5.19 12-storey structure with and without VE damping connections, maximum forces in connection

The maximum forces in connections under the Kobe earthquake, for undamped

structures were in range 104.42 -340.62 kN (45.42 - 136.32 kN) with the highest

value of 340.62 kN (136.32 kN) at the 2nd storey then decreased up to 4th storey,

then up to 6th storey is increased and once again decreased up to the top. However,

with the introduction of VE damping connections in the structure, the forces in

connections were decreased by an average of 80.68% (73.6%).


137

The maximum forces in connections under Northridge earthquake, in the undamped

structure were in range 73.29-487.86 kN (34.33 -195.19 kN) with the highest value

of 487.86 kN (195.19 kN) at 2nd storey, then decreased up to the top. While, with the

introduction of VE damping connections in the structure, the forces in the

connections decreased by an average of 77% (70.04 %.)

As it can be seen from Fig. 5.20, the maximum differential displacement between the

frame and facade under the El Centro earthquake for the undamped structure were in

range 3.49-15.38 mm (1.4- 6.16 mm) with the highest value of 15.38 mm (6.16 mm)

at 2nd storey then decreased toward the 6th storey, then increasing up to the 9th

storey and once again decreasing toward the top. However, with the introduction of

VE damping connections to the structure, the differential displacement between the

frame and facade was reduced by an average of 78.46% (78.17%).

The differential displacement between the frame and facade under the Kobe

earthquake, for the undamped structure, was in range 4.78 - 17.48 mm (1.91- 6.99

mm) with the highest value of 17.48 mm (6.99 mm) at 2nd storey, then decreased

toward the 6th storey, and then once again rapidly increased in 7th storey and then

decreased up to the top. On the other hand, with the introduction of VE damping

connections to the building facade system, the differential displacement between the

frame and facade was reduced by an average of 81.47% (81.14%).

The maximum differential displacement between the frame and facade under the

Northridge earthquake, for the undamped structure, were in range 2.78-25.07 mm

(1.11 – 10.02 mm) with the highest value of 25.07 mm (10.2 mm) at 2nd storey and

then decreased up to the top. However, with the insertion of the VE damping

connections in the structure the differential displacement between the frame and

facade was reduced by an average of 80.49% (80.27%).


138


-2

2

6

10

14

18

22

26

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

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S.9

S.1

0S

.11

S.1

2


Diff

ere

nti

al D

isp

lace

me

nt(

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)

UN

VE

a) Maximum differential displacement, results under 0.5g


-1

1

3

5

7

9

11

S.2

S.3

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S.5

S.6

S.7

S.8

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.9S

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S.5

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S.1

2


Diff

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al D

isp

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me

nt(

mm

)

UN

VE

b) Maximum differential displacement, results under 0.2g


As can be seen from Fig. 5.21, the maximum interstorey drift under the El Centro

earthquake, in the undamped structure were in range 19.37-35.14 mm (7.75-14.05

mm) with the highest value of 35.14 mm (14.05 mm) at 2nd storey decreasing up to

the 6th storey, then increasing up to the 10th storey and then decreasing up to the top.

When VE damping connections were introduced to the structure, the interstorey

drifts decreased by an average of 76.18% (76.18%). The maximum interstorey drifts

under the Kobe earthquake, for the undamped structure, were in range 19-40 mm

(9.15- 16.05 mm) with highest value of 40 mm (16.05 mm) at the 2nd storey


139

decreasing up to 6th storey, then increasing up to 8th storey and then decreasing up

to the top. However, with the insertion of VE damping connections in the structure,

the maximum interstorey drifts were reduced by an average of 80.09% (80.08%).

12 Storey Building Facade System

0

10

20

30

40

50

60S

1-2

S2

-3S

3-4

S4

-5S

5-6

S6

-7S

7-8

S8

-9S

9-1

0S

10

-11

S1

1-1

2

S1

-2S

2-3

S3

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4-5

S5

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S7

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11

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Inte

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rift

(m

m)

UN

VE

a) Maximum interstorey drift, results under 0.5g


0

5

10

15

20

25

S1

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2-3

S3

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10

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0-1

1S

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12

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2-3

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6-7

S7

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S7

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10

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0-1

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11-

12


Inte

rsto

rey

Dri

ft (m

m)

UN

VE

b) Maximum interstorey drift, results under 0.2g

Figure 5.21 12-storey structure with and without VE damping connections, maximum interstorey drifts

The interstorey drift under the Northridge earthquake, for the undamped structure,

were in range 17.59-57.47 mm (7.04- 22.86 mm) with the highest value of 57.47 mm

(22.86 mm) at the 3rd storey and then decreased toward the top. On the other hand


140

with the introduction of VE damping connection to the structure, the interstorey

drifts were reduced by an average of 78.6 % (78.6%).


0

0.0003

0.0006

0.0009

0.0012

0.0015

0.0018

0.0021

0.0024

0.0027S

.2S

.3S

.4S

.5S

.6S

.7S

.8S

.9S

.10

S.1

1S

.12

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Dis

tort

ion

(R

ad

ian

)

UN

VE

a) Maximum distortion of façade, results under 0.5g


0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2

S.2

S.3

S.4

S.5

S.6

S.7

S.8

S.9

S.1

0S

.11

S.1

2


Dis

tort

ion

(R

ad

ian

)

UN

VE

b) Maximum distortion of façade, results under 0.2g

Figure 5.22 12-storey structure with and without VE damping connections, maximum distortion of façade

As can be seen form Fig. 5.22, the maximum distortion of facade under the El Centro

earthquake, for the undamped structure were in range 0.00119-0.0020 radian

(0.00048 - 0.00081 radian). However, with the introduction of VE damping

connection to the structure, the distortion of facade was reduced by an average of

76.41% (76.36%).


141


structure were in range 0.00104- 0.00214 radian (0.000418 - 0.000857 radian).

However, with the introduction of VE damping connections to the structure, the

distortion of facades was reduced by an average of 80.96% (80.92%). The maximum

distortion of the facade under the Northridge earthquake, for the undamped structure

were in range 0.001703- 0.00253 radian (0.00068 - 0.00101 radian). On the other

hand, with the insertion of VE damping connections in the structure, the distortion of

facades was reduced by an average of 79.42% (79.40%).

From Figures 5.18 - 5.22 it can be seen that the seismic responses of building facade

system associated with maximum force in connections, deformation in connection,

differential displacements, interstorey drifts, distortions, differential displacements,

displayed similar trends. The undamped building facade systems produced larger

values of all the response parameters compared to those of the building facade

system with VE damping connections. The structures fitted with VE damping

connections exhibited significantly high improvement in all investigated parameters,

under the El Centro, Kobe and Northridge earthquakes.

5.5. Seismic responses of 12-storey structure with precast concrete facade - effect of damping to stiffness ratio

A 12-storey structure as described in Section 5.4 was considered. This structure was

analysed under 2 different conditions to investigate the influence of damping to

stiffness.

The value of dashpot damping ( Cd ) was determined to be 20,000 kN/m and the

value of spring stiffness ( kd ) was varied to be in the range 5,000 - 35,000 kNs/m.

This gave the damping to stiffness ratio a range of 4 – 0.55. The value of dashpot

damping ( Cd ) was determined to be 35,000 kNs/m and the value of spring stiffness(

kd ) was varied to be in the range from 5,000 - 35,000 kN/m. The damping to

stiffness ratio for this case had the range 7 – 1.

A dynamic analysis of this structure with VE damping connections placed in all

storeys were conducted under the El Centro earthquake excitations scaled to PGA

0.3g. The connections were modelled as elastic spring and dashpot in parallel, as

described earlier and were placed horizontally at each storey of the structure. The


142

value of dashpot damping ( Cd ) was determined to be 20,000 kN/m and the values

of spring stiffness ( kd ) were varied in the range from 5,000 - 35,000 kNs/m. The

undamped structure had connections with the spring stiffness (k) of 20,000kN/m for

horizontal connections and spring stiffness (k) of 30,000kN/m for vertical

connections.

The seismic loading applied to the structural system was horizontal, therefore, in this

study only the behaviour of the horizontal connections was considered. The effect of

the connection stiffness and damping on the seismic response of the structural system

was investigated. The response of the structure is obtained for selected time steps of

the input earthquakes accelerogram.

Important results pertaining to the reductions in the peak values for the differential

displacement between frame and facades under the scaled El Centro earthquake

excitations are summarised in Table 5.2. The results for reductions in all investigated

parameters of the structure inserted with constant VE damping and varying stiffness

properties displayed overall very high performance.

Table 5.2 Maximum values of the response quantities, considering connections stiffness kd and damping coefficient Cd

The best performance with the highest reduction in all investigated parameters was

recorded for the damping to stiffness ratio of 0.55, which had a spring stiffness of kd

= 35,000 kN/m. The results showed that the stiffness parameter of kd = 35,000 kN/m

caused the lowest values of differential displacement in range 0.25-3.99 mm. The


143

increase in spring stiffness (kd) had different effects in the results across the storeys

as shown in Table 5.2. There was no regular pattern of decrease in the differential

displacement.

A 12-storey structure with the same load and properties as before was considered. At

this stage of the investigation, the values of spring stiffness were in the range 5,000 -

35,000 kN/m., while the damping parameter of Cd = 35,000 kNs/m was kept

constant. A summary of the results indicating reductions in the differential

displacement between frame and facades under the El Centro earthquake excitations,

are summarised in Table 5.3.

In general, the results showed good seismic control of the facade differential

displacement with respect to all investigated parameters for the range of stiffness

5,000-20,000 kN/m. However, an increase in the stiffness of the springs over the

value of 25,000 kN/m resulted in increases in the value at second storey for the

investigated parameter.

Table 5.3 Maximum values of the response quantities considering connections stiffness kd and damping coefficient Cd

As can be seen in Table 5.3, the best performance of the structure for the investigated

parameter was achieved when the spring stiffness (kd) was 25,000 kN/m, for the

damping to stiffness ratio of 1.4. However the spring stiffness (kd) of 20,000 kN/m

produced very close values of reduction for the investigated parameter. In general,

the structure inserted with VE damping connections, having dashpot damping of


144

Cd = 35,000 kNs/m produced better reductions in the differential displacement

between the frame and facade, compared to the structure with VE damping

connections having the dashpot damping value of Cd = 20,000 kNs/m.

Fig.5.23 show the differential displacement between the frame and facade for the

undamped structure and structure inserted with VE damping connections having

dashpot damping values of Cd = 20,000 kNs/m and Cd = 35,000 kNs/m. From this

figure it can be observed that both damped structures are very effective in controlling

the seismic response in the system and, as expected the system with the higher

damping value performed better. The effectiveness of energy absorbing connections

is clearly evident from this below Figure.


5.6. Seismic Analyses of 12-storey building facade system for load case 2: - effects of facade mass

A 12-storey building structure with the properties and loads as described in section

5.4 was considered. The main purpose of this investigation was to study the effect of

the facade mass on the behaviour of the building facade system. The facade panels

had a range of mass and varied from those corresponding to the lightest material such

as aluminium to the heaviest material such as marble. The structure with the lightest

facade panels represented 0.81% of the total structural mass. It was followed by the

middle mass facade panels representing 3.81%, 8.98%, 14.13%, 19.80%, 22.85% of

structure mass and finally the heaviest facade panels represented 26.58% of overall


145

mass of the building structure. Connections of the undamped structure had the

stiffness parameters of k = 35,000 kN/m and k = 20,000 kN/m for the vertical and

horizontal connections respectively. The structure inserted with the VE damping

connections had the stiffness and damping parameters of Cd = 35,000 kNs/m and

kd = 20,000 kN/m.

The structure was subjected to the El Centro earthquake excitations, scaled to PGA

of 0.3g. The response of the structure was obtained for selected time steps of the

input earthquakes accelerogram. Fig 5.24 displays the differential displacement

between facade and frame.

The result of the investigated parameter for the structure with facade panels of mass

ratio of 0.81% was compared with that of the structure with facade panels of higher

mass ratio. As can be observed in Fig. 5.24, the differential displacement between

frame and facades under the El Centro earthquake in the undamped structure with

panels of 0.81% of mass ratio were in range 0.82-7.36 mm, however with the

insertion of the VE damping connections in the building facade system the

differential displacement was reduced by 73.8%.

The differential displacement under the El Centro earthquake in the undamped

structure with panels of 3.81% of mass ratio were in range 0.75-8.05 mm, on the

other hand with the insertion of the VE damping connections in the building facade

system the differential displacement was reduced by 76.4%.

The differential displacement between frame and facades under the El Centro

earthquake in the undamped structure with panels of 8.98% of mass ratio were in

range 1.25-8.51 mm, When the VE damping connections were fitted a reduction of

78.4% for differential displacement was obtained.

In terms of panels of 14.13% of mass ratio, the efficiency of the VE damping

connections was even higher under the El Centro earthquake when the maximum

differential displacement of 1.62-8.42 mm for the undamped structure was reduced

by an average of 79.3%, after the VE damping connections were fitted in the

structure.


146

The differential displacement between frame and facades under the El Centro

earthquake in the undamped structure with panels of 19.80% of mass ratio varied in

range from 2.09-9.23 mm, while with the introduction of the VE damping

connections in the structure the differential displacement was reduced by an average

of 78.3%. Structures with panels of 22.85% of mass ratio experienced differential

displacement were in range 2.49-10.28 mm. However, after the VE damping

connections were fitted, the differential displacement was reduced by an average of

76.1%.


0123456789

10111213

0.81% 3.81% 8.98% 14.13% 19.80% 22.85% 26.58%

Diff

ere

nti

al

Dis

pla

cem

en

t (m

m)

S.2 S.4 S.6 S.8 S.10 S.12

Str

uct

ure

with

VE

co

nn

.

Un

da

mp

ed

Str

uct

ure

Figure 5.24 Differential Displacements in 12-storey structure- effect of façade mass

A slightly lower reduction in the differential displacement was achieved under the El

Centro earthquake for structure with panels of 26.58% of mass ratio. The differential

displacement in the undamped structure were in range 0.49-11.86 mm, however with

the insertion of the VE damping connections in the building facade system the

differential displacement was reduced by 67.2%. In general, as can be seen from

these results, the differential displacement between frame and facade under the El

Centro earthquake regularly decreased towards the uppermost storeys. Figure 5.24

and Table 5.4 show the differential displacement between frame and facade,

considering the facade mass ratio. In this figure VE denotes the results of the damped

systems.

From this study, it can be inferred that:

i. For the undamped structure significant increase in the mass ratio resulted in

higher average percentage reductions in differential displacement.


147

ii. For the damped structure increase in the mass ratio up to 15% resulted in the

increase of average percentage reduction in differential displacement

followed by smaller reductions in this parameter at higher mass ratios.

Table 5.4 Maximum values of the response quantities considering facade mass ratio

UN VE UN VE UN VE UN VE UN VE UN VE UN VES.2 7.36 2.51 8.05 2.53 8.51 2.68 8.42 2.79 9.23 3.01 10.28 3.13 11.86 3.28S.4 5.32 1.82 5.92 1.82 6.72 1.93 6.69 2.04 7.29 2.21 7.85 2.3 8.94 2.42S.6 4.97 1.41 5.34 1.37 6.22 1.45 6.96 1.52 5.53 1.63 5.82 1.686.26 1.77S.8 3.71 0.95 4.47 0.91 4.84 0.97 6.02 1.01 5.33 1.1 3.36 1.15 3.36 1.21S.10 2.59 0.52 2.8 0.5 3.48 0.53 4.84 0.57 5.87 0.62 4.5 0.64 1.81 0.67S.12 0.82 0.12 0.75 0.12 1.25 0.131 1.62 0.15 2.09 0.17 2.49 0.17 0.49 0.19

0.81% 3.81% 8.98%Storeys

14.13% 19.80% 22.85% 26.58%

Differential Displacement (mm)

5.7. Seismic responses of 12-storey building with glass facades for load case 1

The twelve-storey building facade system had an overall height of 48 m and a span

of 8m and was described in chapter 3. The Aluminium frame that was used around

the glass facade had a thickness of 0.002 m and width of 0.060 m. The rubber

sealants used at the junctions between the aluminium frame and glass facades had a

thickness of 0.012 m and width of 0.002 m. Each storey contained a total of 8 glass

facades with dimensions of 2m x 2m and thickness of 0.012 m. The concrete

structural frame was connected to the Aluminium façade frame by a total of 4

vertical and 4 horizontal connections. All connections were assumed to have a

stiffness of k= 5000 kN/m. In this stage of the investigation uniformly distributed

loads of 40 kN/m applied to the lower storeys beams while the load distributed to the

top storey beam was 34 kN/m. Since the seismic loading applied to the structural

system was horizontal, only the behaviour of the horizontal connections was

considered.

The energy absorbing connections were modelled by spring and dashpot in parallel

as before and were placed in the horizontal direction. Spring stiffness and dashpot

damping were considered to have the values of 5,000 kN/m and 20,000 kNs/m

respectively. The vertical connections were modelled as spring connections with a

stiffness of 5,000 kN/m. The models were analysed under the El Centro earthquake

excitations scaled to have a PGA of 0.1g. Firstly, the effect of the horizontal

connection stiffness on the seismic response of the building facade system was

investigated, with no damping. Later on, the building facade systems fitted with the


148

VE damping devises were reanalysed to investigate the effectiveness of energy

absorbing connections.

As mentioned before the seismic response of the building facade system can be

evaluated in many ways. However computation of the deformation of connections in

terms of (extension/compression of spring), differential displacement between facade

and frame, distortion of facade, and interstorey drift reveal significantly effect of the

earthquake on the building facade systems.

Figs. 5.25 - 5.29 illustrate the maximum responses in terms of displacements


as well as distortion of facades under the El Centro earthquake. Additional results

can be found in Appendix C.

As can be observed from Fig. 5.25 the maximum deformation of connections for the

undamped structure was in the range 0.501-2.2 mm. On the other hand, with

insertion of VE damping connections in the structure, the deformation of connections

was reduced by an average of 50.37%. In these Figures UN and VE denote the

results of the undamped and damped systems respectively.


0

0.5

1

1.5

2

2.5

S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 S.11 S.12

El-Centro

De

form

ati

on

(m

m)

UN

VE

Figure 5.25 12-storey structure with and without VE damping connections, maximum deformation in connections

As can be seen from Fig. 5.26, the maximum forces in connection under the El

Centro earthquake, for undamped structure were in range 2.50-11.01 kN. However,


149

with the introduction of VE damping connections to the structure, the forces in

connections were reduced by 50.42%.


0

2

4

6

8

10

12

S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 S.11 S.12

El-Centro

Fo

rce

(kN

)UN

VE

Figure 5.26 12- storey structure with and without VE damping connections, maximum force in connections

In terms of reduction in the differential displacement between frame and facade,

surprisingly a huge range of results was displayed.


0

0.5

1

1.5

2

2.5

3

S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 S.11 S.12

El-Centro

Diff

ere

nti

al D

isp

lace

me

nt(

mm

)

UN

VE

Figure 5.27 12- storey structure with and without VE damping connections, maximum differential displacement between frame and façade

From the Fig. 5.27 it can be observed that the maximum differential displacement for

undamped structure experienced under the El Centro earthquake, was in the range

0.17- 2.48 mm. However, with the introduction of VE damping connections in the

structure, the differential displacement between the frame and facade was reduced by


150

an average of 30.52%. The results show that in storeys 1-8 and 12 a high level of

efficiency was obtained, however in storeys 9-11 the VE damping connections did

not demonstrate efficiency and slight increase in displacement was recorded at these

storeys.

A significantly high damping connections performance was obtained also in terms of

reduction in the maximum interstorey drift. (Fig. 5.28) The maximum interstorey

drift occurred between the first and second storey of the structure. The interstorey

drift under the El Centro earthquake for the undamped structure ranged 1.2-7.0 mm.

On the other hand, with the introduction of VE damping connections to the structure,

the interstorey drift reduced by an average of 32.12%. The results show that the VE

damping connections performed very well in the lower storeys, however the

efficiency of the VE damping connections for storeys 9-11 was very low.


0

2

4

6

8

10

12

S0

-1

S1

-2

S 2

-3

S 3

-4

S 4

-5

S 5

-6

S 6

-7

S 7

-8

S 8

-9

S 9

-10

S 1

0-1

1

S 1

1-1

2

El-Centro

Inte

r-S

tore

y D

rift

(mm

) UN

VE


High efficiency of the damping connections was obtained also in terms of reduction

in differential displacement between upper and lower facade. From Fig. 5.29 it can

be observed that maximum differential displacement experienced under the El

Centro earthquake for undamped structure, was in range 0.41-4.49 mm. With the

insertion of a VE damping connection to the structure the differential displacement

between upper and lower facade reduced by an average of 28.11%.


151


0

1

2

3

4

5

S.2

-3

S.3

-4

S.4

-5

S.5

-6

S.6

-7

S.7

-8

S.8

-9

S.9

-10

S.1

0-1

1

S.1

1-1

2

El-Centro

Diff

ere

nti

al D

isp

lace

me

nt

(mm

)

UN

VE

Figure 5.29 12-storey structure with and without VE damping connections, maximum differential displacement between upper and lower facades

The results demonstrate that the VE damping connections showed reasonably high

efficiency in the lower storeys; however the efficiency of the VE damping

connections for storeys 10 and 11 was insignificant. The maximum stress in the

facade panel under the El Centro earthquake for the undamped structure was in range

0.40-5.60 MPa. After the VE damping connections were fitted in the structure the

maximum stress was reduced to range 0.19-2.66 MPa.



connections considering load cases 1 and 2, under the El Centro, Kobe and

Northridge earthquakes were investigated. The structures fitted with precast concrete

facades were investigated considering load case 1 and 2, under all three selected

earthquake excitations, while the structures fitted with glass facades were

investigated considering case 1, under the El Centro earthquake excitation only.

In general, the results from the undamped structures revealed high levels of the

deformation and axial forces in connections, differential displacement between

facade and frame, distortion of facade, and interstorey drifts under all the selected

earthquake excitations. Considering load case 1, the largest values for all the

investigated parameters, in the structure fitted with precast concrete facade were

experienced under the El Centro earthquake. It was followed by the significantly

high values obtained under the Northridge earthquake. The values obtained under the


152

Kobe earthquake were slightly lower. Considering the load case 2, the biggest values

for all the investigated parameters occurred under the Northridge earthquake. It was

followed by the notably high values obtained under the Kobe earthquake. The values

obtained under the El Centro earthquake were the lowest.

The results from the undamped structure showed that in most cases, the vertical load

had a significant affect on the behaviour of the building facade system. The structure

under the larger load case (Case 1) has produced larger values in response compare

to the smaller load case (Case 2), when subjected to the El Centro and Northridge

earthquake excitations. In the case of the Kobe earthquake the response values

produced under both load cases were approximately the same.

The overall results showed that the incorporation of the VE damping connections to

the building facade systems enhanced the reliability of the energy absorption and

decreased the seismic effect on facade at the all level of the structure. However,

while considering load case 1, the performance of the VE damping connections in

the upper storeys provided better mitigation of the seismic load than in the lower

storeys. Reduction in all investigated parameters usually increased towards the

uppermost storeys under all three earthquake excitations. Considering the load case

2, while investigating the deformation and forces in connections, the result revealed a

better performance of the VE damping connections in the middle levels, providing

better mitigation of the seismic load than in the lower and upper levels. In the case of

the differential displacement between frame and facade, distortion of facades and

interstorey drift, the VE damping connections provided better mitigation of the

seismic load in the upper storeys than the lower storeys.

Considering the load case 1 (larger load), the results showed that the greatest average


between facade and frame, and the distortion of facade was experienced under the El

Centro earthquake excitation, which exhibit a wide band of dominant frequencies

(0.39-6.39Hz). The second highest average deflection reduction occurred under the

Northridge earthquake, which had a strongly dominant narrow frequency range

(0.14-1.07 Hz). In the case of the Kobe earthquake excitation, which was

characterised by a strongly narrow dominant frequency range (0.29-1.12 Hz) the

efficiency of the VE damping connections was slightly lower. The behaviour of the


153

structure under the all three earthquakes demonstrated the complex behaviour of the

building facade system under seismic loads.

In terms of the reduction of deformation and axial forces in connections, differential

displacement between frame and facade and distortion of the facade under the El

Centro, Kobe and Northridge earthquake excitations in the second storey level across

the width of the structure (horizontal direction), the results obtained were very close.

Considering the load case 2 (smaller load), the results showed that the greatest

average reduction in deformation and forces in connections, differential displacement


Kobe earthquake excitation, The second highest average reduction occurred under

the Northridge earthquake, while in the case of the El Centro earthquake, the

efficiency of the VE damping connections was slightly lower. Similar to the case 1,

the results for the load case 2 displayed a complex behaviour of the building facade

system under the all three earthquakes.

For the undamped structure increase in the mass ratio resulted in higher average

percentage reductions in differential displacement. However, for the damped

structure increase in the mass ratio up to 15% resulted in the increase of average

percentage reduction in differential displacement followed by smaller reductions in

this parameter at higher mass ratios.

In terms of the structure fitted with glass facade the undamped structure experienced

significantly high levels of the deformation and axial forces in connections,

differential displacement between facade and frame, distortion of facade, and

interstorey drift under the selected earthquake excitations. Overall, the insertion of

the VE damping connections in the structure provided significant reductions in all

investigated parameters.

The efficiency of the energy absorbing connections while considering the

deformation and force in connections was more or less the same across all storeys.

However, considering the differential displacement between frame and facade,

interstorey drift and the differential displacement between upper and lower facades,

the VE damping connections provided the best performance in the lower storeys.

The results also demonstrated that the effectiveness of the VE damping connections


154

for storeys 10 and 11 was insignificant. This can be explained by the fact that the

natural frequency of the 12 storey building is within the frequency of dominant

motions of the El Centro earthquake. The stresses found in the glass panel in the

undamped structure were significantly high; however with the insertion of the VE

damping connections, the maximum stress in the glass panel was reduced to an

acceptable limit in which the panel will not break.


155

Chapter 6



156


6.1. Introduction

The fourth structural type investigated in this study was represented by 18-storey

structures, (Fig. 6.1). These structures have the load and material properties

described in Sec. 3.2 and 3.2.2. The facade panels were placed in all storeys, at 0.05

m distance from building frame as before. The structure was analysed considering 2

load cases, as will be explained in Section 6.2.1. These structures were analysed

under the El Centro, Kobe and Northridge earthquakes scaled to PGA 0.3g to

facilitate comparison of results. The effect of the connection stiffness and the effect

of the damping on the seismic response of the structural system were investigated.

The results from the finite element analysis of the undamped structure and structure

fitted with VE damping connections are presented. The 18-storey models have

natural frequencies within the range of dominant earthquake modes; hence this study

also includes resonant conditions.

6.2. 18-storey building facade system

6.2.1. Description of 18-storey structural models

These structures have the columns and beams with cross-sectional dimensions of 0.7

x 0.7 m and 0.75 x 0.7 m respectively, and the spans were 8 m. The height of each

storey was 4.0 m, which gave an overall height of 72 m. The connections between

the frame and facade were modelled by springs in the horizontal and vertical

direction to replicate the stiffness of original connection. Spring stiffness was

considered to have the value of 20,000 kN/m for horizontal and 35,000 kNs/m for

vertical connections respectively. The energy absorbing connections between the

frame and facade were modelled by springs and dashpots and were placed in

horizontal direction. Spring stiffness and dashpot damping were considered to have

the value of 20,000 kN/m and 35,000 kNs/m, respectively as before. The vertical

connections were modelled as spring connections, having a stiffness of 35,000 kN/m.

Both damped and undamped structures were analysed under the three selected

earthquake excitations, considering two separate load cases, to investigate the

influence of load magnitude.


157

Load case 1: The vertical loading on the structure was in the form of uniformly

distributed loads of 75 kN/m applied to the lower storey beams while the load

distributed to the top storey beam was 50 kN/m.

Load case 2: The vertical loading on the structure was in the form of uniformly

distributed loads of 40 kN/m applied to the lower storey beams while the load

distributed to the top storey beam was 34 kN/m.

Figure 6.1 Model of 18-storeys, building facade system





Modes Natural

Frequency(Hz) Period of

Vibration(T/Sec) First 0.63 1.58

Second 1.92 0.52 Third 3.32 0.3


158


As mentioned previously, the deformation of connections in terms of (extension /

compression of spring), axial forces in springs, differential displacement between

facade and frame, distortion of facade, and the interstorey drifts were considered to

be the key parameters in this study.

The connections between the frame and facade in an undamped structure were

modelled by springs in the horizontal and vertical direction as discussed before.

Spring stiffness k was considered to have the value of 20,000 kN/m for the horizontal

and 35,000 kN/m for the vertical connection respectively as before. The connections

between the frame and facade in the damped structure were modelled by springs and

dashpots and were placed in the horizontal direction as mentioned earlier. Spring

stiffness and dashpot damping were considered to have the value of kd = 20,000

kN/m and Cd = 35,000 kNs/m respectively. The vertical connections were modelled

as spring connections, having a stiffness of k = 35,000 kN/m.

The results in terms of the maximum responses of differential displacements between

frame and facade, deformations and forces in connections, distortion of facades as

well as interstorey drifts in all storeys of the structure for the undamped structure and

structure inserted with VE damping connections across the height of the structure (in

panel 1) under the El Centro, Kobe and Northridge earthquakes are presented in

Figures 6.2-6.6. Additional results can be found in Appendix D.

Herein x-axis refers to the storey number which is denoted by S. <number>; the

“number” represents storey number (where n = 1 – 18), thus the UN and VE

represent the undamped and damped structures respectively.

In general, the results show that in most cases the lower storeys experienced the

largest values for all investigated parameters under selected earthquakes, for both

undamped structures and structures fitted with the VE damping connections. As can

be observed from Fig. 6.2, the deformation in connections for the undamped

structure under the El Centro earthquake for lower and middle storeys oscillated in

the range 10-14mm, while for upper storeys were significantly lower. However,

when the VE damping connections were installed reduction in the range by an

average of 76.22% was obtained across all storeys. In the case of the Kobe


159

earthquake, the deformations of connections were in range 1.88-8.11mm for the

undamped structure. However, with the insertion of the VE damping connections the

deformation was reduced by an average of 76.50 % across all storeys. The maximum

deformation of connections under the Northridge earthquake was in range 1.8-

10.7mm. On the other hand, after the VE damping connections were introduced, the

deformation was reduced by an average of 67.95%.

Overall, the results showed that the largest deformation of connections in the

undamped structure was obtained under the El Centro earthquake excitation and only

a slightly lower deformation was experienced under the Northridge earthquake. The

deformation that occurred during the Kobe earthquake was the lowest. However, the

addition of the VE damping connections in the structure notably changed the effect

of the seismic loading on the behaviour of the structure and produced desirable

results. In terms of reduction in the deformation of connection, the best results were

recorded under the Kobe earthquake.


0123456789

101112131415

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8


De

form

ati

on

(m

m)

UD

VE

Figure 6.2 18-storey structure with and without VE damping connection, maximum

deformation in connection

The second greatest reduction in the peak values of the deformation was achieved

under the El Centro earthquake. The reduction in the deformation of connections

achieved under the Northridge was the lowest. As can be seen from these results,

under all three selected earthquake excitations, the decrease in deformations of

connections was normally greater towards the highest storeys. In general, the VE


160

damping connections operated very well on all storeys and the range of the results

was very close across all selected earthquakes.

As can be seen from Fig. 6.3, the axial forces in connections for the undamped

structure under the El Centro earthquake for lower and middle storeys oscillated in

the range 201.78-286.3kN, whereas the figures for the upper storeys were

significantly lower. After the VE damping connections were installed an average

reduction of 76.20% was obtained across all storeys.

In the case of the Kobe earthquake, the axial forces in connections ranged from

37.71-162.41kN for the undamped structure. With the insertion of the VE damping

connections the deformations were reduced by an average of 76.47% across all

storeys. The maximum deformation of connections under the Northridge earthquake

was in range 36.32-214.17 kN. On the other hand, when the VE damping

connections were inserted, the deformation reduced by an average of 67.94%.


0

50

100

150

200

250

300

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8


Fo

rce

(kN

)

UD

VE

Figure 6.3 18-storey structure with and without VE damping connection, maximum

force in connection

In general, the largest amount of axial forces in connections in the undamped

structure was obtained under the El Centro earthquake excitation. It was followed by

the axial forces obtained under the Northridge earthquake. The axial forces which

occurred under the Kobe earthquake were the lowest.


161

In terms of reduction in the peak values of axial forces, the best results were recorded

under the Kobe earthquake. The second greatest reduction in the peak values of the

axial forces was achieved under El Centro the earthquake and reduction in the axial

forces of connections achieved under the Northridge earthquake was the lowest. As

can be observed from the results, under all three earthquake excitations, a greater

decrease in axial forces in connections was recorded in the higher storeys.

As can be seen from Fig. 6.4, the largest differential displacement between frame and

facade in the undamped structure was obtained under the El Centro earthquake. The

Kobe earthquake demonstrated the least displacement with Northridge falling in

between.

In terms of reduction in the differential displacement between frame and facade, a

surprisingly wide range of results was produced under the Kobe earthquake. Fig.6.4

demonstrates that the maximum differential displacement between frame and facade

occurred under the Kobe earthquake, with the undamped structure were in range

0.41- 8.3 mm. With the insertion of the VE damping connections the differential

displacement between frame and facades was reduced by an average of 59.58%. The

results show that in storeys 1-10 and 14-18 a high level of efficiency was obtained

through the VE damping connections; however this was not the case in storeys 11-13

where an increase in differential displacement was recorded.

As described in Section 3.6 the Kobe earthquake can be characterised as an

excitation with a very narrow range of dominant frequencies and also with several

strong motions. The natural frequency of 18-storey structure is within this range.

Based on this, it is possible that this increase in differential displacement is due to

resonant problems.

The maximum differential displacement between frame and facades experienced

under the El Centro earthquake for the undamped structure ranged from 1.8- 14.65

mm. Maximum displacements was observed in lower storeys and displacement

reduced uniformly as storey height increased. However, with the introduction of the

VE damping connections, the differential displacement between frame and facades

was reduced by an average of 67.64% across all storeys. The maximum differential

displacement between frame and facade under the Northridge earthquake, in the


162

undamped structure were in range 0.67- 10.98 mm. After the VE damping

connections were fitted the differential displacement between frame and facade was

reduced by an average of 65.79%.

The results clearly indicated that the reduction in the differential displacement

between frame and facade under the El Centro and Northridge earthquake excitations

demonstrated the very high efficiency of the VE damping connections. However in

the case of the Kobe earthquake, the energy absorbing connections did not display

improvement in storeys 11-13, where an increase in differential displacement was

recorded. The best results with a significant reduction were recorded under the El

Centro earthquake. The second greatest reduction in the peak values of the

differential displacement was achieved under the Northridge earthquake. The

reduction in the deformation of connections achieved under the Kobe earthquake was

the lowest. Similar trend was observed in the case of the distortion of facade.


0123456789

101112131415

S.2

S.4

S.6

S.8

S.1

0

S.1

2

S.1

4

S.1

6

S.1

8S

.2

S.4

S.6

S.8

S.1

0

S.1

2

S.1

4

S.1

6

S.1

8S

.2

S.4

S.6

S.8

S.1

0

S.1

2

S.1

4

S.1

6

S.1

8


Diff

ere

nti

al D

isp

lace

me

nt

(mm

)

UD

VE



Fig. 6.5 illustrates the results in terms of maximum distortion of facade for the

undamped structure and structure fitted with VE damping connections. As can be

seen in this figure, distortion of facade for the undamped structure under the El

Centro earthquake for middle and upper storeys oscillated in the range 0.0012-

0.002mm, while for the lower storeys the results were significantly lower. However,

when the VE damping connections were installed an average reduction of 63.42%

was obtained across all storeys.


163

The distortion of the facade for the undamped structure under the Kobe earthquake

for upper storeys ranged from 0.00132-0.00148 radian, while for lower and middle

storeys the distortion was radically less. When VE damping connections were

embedded an average reduction of 51.37% was obtained across storeys 1-11 and 16-

18. However in storeys 12-15 the VE damping connections did not display the same

level of efficiency with an increase in distortion being recorded at these levels.

As mentioned earlier the Kobe earthquake can be characterised as an excitation with

a very narrow range of dominant frequencies (0.29-1.12 Hz) with several strong

motions. The natural frequency of an 18-storey structure is within this range.

Because of this, it is possible that this increase in differential displacement is due to

resonant problems. The distortion of facade for the undamped structure under the

Northridge earthquake for middle and upper storeys oscillated in the range 0.0016-

0.0020mm, while for the lower storeys the results were significantly lower.

However, when the VE damping connections were installed an average reduction of

64.15% was obtained across all storeys.

The result clearly demonstrated that the largest differential displacement between

frame and facade in the undamped structure was obtained under the El Centro

earthquake excitations. Kobe demonstrated least displacement with Northridge

falling in between. In terms of reduction in the distortion of facades, the best results

were recorded under the Northridge earthquake. The second greatest reduction in the

peak values of the distortion of facades was obtained under the El Centro earthquake.

The reduction in the distortion of facades achieved under the Kobe earthquake was

the lowest.


164


-0.0002

0.0001

0.0004

0.0007

0.001

0.0013

0.0016

0.0019

0.0022

0.0025

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8

Kobe Northridge

Dis

tort

ion

(R

ad

ian

)UD

VE

Elcentro

Figure 6.5 18-storey concrete frame with and without VE damping connections,

maximum distortion of façade

Fig. 6.6 illustrates, that the largest interstorey drift in the undamped structure was

once again obtained under the El Centro earthquake. The Kobe earthquake

demonstrated the least displacement. The displacement occurred under Northridge

earthquake was somewhere between.

In terms of reduction in the interstorey drift, a huge range of results was

unexpectedly displayed under the Kobe earthquake. Fig.6.6 demonstrates that the

maximum interstorey drift under the Kobe earthquake, for the undamped structure in

the upper and lower storeys fluctuated in the range 7.70- 19.32 mm, while the results

for the middle storeys were significantly lower. When the VE damping connections

were installed an average reduction of 62.15% was obtained across all storeys.

The results show that in storeys 1-10 and 16-18 a high level of efficiency was

achieved with the VE damping connections; however this was not maintained in

storeys 11-15 where an increase in the interstorey drift was recorded.

The maximum interstorey drift experienced under the El Centro earthquake for the

undamped structure was in the range 15.38- 34.13 mm. However, with the

introduction of the VE damping connections, the interstorey drift was reduced by an

average of 66.41% across all storeys. The maximum interstorey drift under the

Northridge earthquake, in the undamped structure were in the range 7.30- 26.76 mm.


165

After the VE damping connections were fitted the interstorey drift was reduced by an

average of 63.34%.

Overall, best results with the greatest reduction were recorded under the El Centro

earthquake. The next greatest reduction in the peak values of the interstorey drifts

was achieved under the Northridge earthquake. Under these earthquake excitations, a

greater reduction in interstorey drift usually occurred in the uppermost storeys. The

reduction in the interstorey drifts achieved under the Kobe was lower than the El

Centro and Northridge earthquakes. As can be seen from these results, under the

Kobe earthquake, the VE damping connections did not demonstrated its efficiency in

storeys 11-15 where an increase in the interstorey drift was recorded.


0

5

10

15

20

25

30

35

S.1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18

S.1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18

S.1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18


Inte

rsto

ery

Drif

t (m

m)

UN

VE


interstorey drift

The results signify that so far in the majority of the cases the lower storeys

experienced the highest values in the response for all considered parameters under

both undamped and damped structures. For this reason, the behaviour of the structure

under the seismic loading across the width of the structure (horizontal direction) was

studied only in the lower storey. Figures 6.7 - 6.10 demonstrates the results of

deformation in connections, forces in connections, the differential displacement

between frame and facade and the distortion of facade under the El Centro, Kobe and

Northridge earthquakes in the second storey level across the width of the structure

(horizontal direction). Additional results can be found in Appendix D. In these

Figures UN and VE represent the undamped and damped structures respectively as


166

mentioned before. Herein n.C-R represents “nth” column right and n.C-L represent

“nth” column left (where n = 1 – 5).

Fig. 6.7 demonstrates that the maximum deformation of connections experienced

under the El Centro earthquake excitations for the undamped structure was 14.66mm.

When the VE dampers were fitted in the structure, the deformation was decreased by

66.91%. The deformation experienced under the Kobe earthquake for the undamped

structure was 8.32 mm. However, after the VE damping connections were fitted, the

deformation decreased by 61.41%.


0123456789

101112131415

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

Elcentro Kobe Northridge

De

form

ati

on

(m

m)

UD

VE

Figure 6.7 18-storey structure with and without VE damping connections (horizontal

direction), maximum deformation in connection

The maximum deformation of connections experienced under the Northridge

earthquake excitations for the undamped structure was 11.07 mm. After the VE

damping connections were fitted in the structure, the deformation of connections

decreased by 46.88%.

Fig. 6.8 demonstrates that the maximum axial force in the connections under the El

Centro earthquake for the undamped structure was 293.3 kN. However, with the

insertion of the VE damping connections in the structure, the axial force was reduced

by 67.19%. The maximum axial force in the connections under the Kobe earthquake,

for the undamped structure was 166.57 kN. With the placement of the VE damping

connections, the axial force was reduced by 61.67%. The maximum force in

connections under the Northridge earthquake, for the undamped structure was 221.54


167

kN. However, after the VE damping connections were fitted, the axial forces were

reduced by 46.87%.


0

50

100

150

200

250

300

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L


Fo

rce

(kN

)UD

VE

Figure 6.8 18-storey structure with and without VE damping connections (horizontal

direction), maximum force in connection

Fig. 6.9 demonstrates that the maximum differential displacement between facade

and frame under the El Centro earthquake, in the undamped structure was 14.91mm.

While with the placement of VE damping connections in the structure, the

differential displacement was reduced by 67.15%. The maximum differential

displacement under the Kobe earthquake, in the undamped structure was 8.46mm.

When the VE damping connections were fitted, the differential displacement was

reduced by 61.56%. The maximum differential displacement under the Northridge

earthquake, in the undamped structure was 11.29 mm. However, after the VE

damping connections were embedded in the structure, the differential displacement

was reduced by 46.94%.

Fig. 6.10 displays the maximum distortion of facades under El Centro Kobe and

Northridge earthquake excitations. As can be observed from Fig. 6.10, the maximum

distortion of facades under El Centro earthquake, for the undamped structure was

0.001227 radian. However, with the insertion of VE damping connections in the

structure, the distortion of facades was reduced by 65.73%.


168


0123456789

10111213141516

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L

1.C

-R2.

C-L

2.C

-R3.

C-L

3.C

-R4.

C-L

4.C

-R5.

C-L


Diff

ere

nti

al D

isp

lace

me

nt

(mm

) UD

VE

Figure 6.9 18-storey structure with and without VE damping connections (Horizontal

Direction), maximum differential displacement between facade and frame


-0.00005

0.00015

0.00035

0.00055

0.00075

0.00095

0.00115

0.00135

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p

1-S

p

2-S

p

3-S

p

4-S

p


Dis

tort

ion

(R

ad

ian

)

UD

VE

Figure 6.10 18-storey structure with and without VE damping connections (horizontal direction), maximum distortion of façade


structure was 0.000702 radian. However, after the VE damping connections were

fitted, the distortion of facades was reduced by 60.27%. The maximum distortion of

facades under the Northridge earthquake, for the undamped structure was 0.001006

radian. When the VE damping connections were introduced, the distortion of facades

was reduced by 50.61%.


169

As can be seen from Fig. 6.7-6.10, the highest values for all the investigated

parameters for the undamped structures were obtained under the El Centro

earthquake excitation. The values obtained under the Northridge earthquake were

lower and the values occurred under the Kobe earthquake was the lowest. Similar

trend was observed from the structure fitted with the energy absorbing connections.

With regards to the reduction in all the investigated parameters, the best results with

a significant reduction in all parameters were recorded under the El Centro

earthquake. The second greatest reduction in the peak values of the all investigated

parameters was achieved under the Kobe earthquake. The reduction in the

parameters achieved under the Northridge was the lowest.



discussed in Section 6.3 were considered. The connections with the same properties

as discussed in Sec. 6.2 were chosen. Uniformly distributed loads of 40 kN/m were

applied to the lower storey beams while the load distributed to the top storey beam

was 34 kN/m as discussed earlier. These structures were analysed under the El

Centro, Kobe and Northridge earthquakes scaled to PGA of 0.3g.

Figures 6.11 - 6.15 illustrate the deformation and axial force in connections, the

differential displacement between facade and frame, the distortion of facade, and the

interstorey drift. Additional results can be found in Appendix D. In these Figures UN

and VE denote the results of the undamped and damped systems respectively.

Fig. 6.11 demonstrates that the maximum deformation of connections under the El

Centro earthquake, for the undamped structure were in the range 1.88- 13.07 mm.

With the insertion of the VE damping connections the differential displacement

between frame and facades was reduced by an average of 72.25%. The results show

that considerably high efficiency of the VE damping connections was obtained in the

storey 1-16, however the efficiency of VE damping connections was significantly

lower in storeys 17 and 18. The deformation of connections under the Kobe

earthquake, for the undamped structure, was in the range 2.6- 7.61 mm. However,

with the introduction of VE damping connection the deformation were reduced by an

average of 68.65%. The deformation of connection under the Northridge earthquake,

for the undamped structure, was in the range 1.87–11.64 mm. While with the


170

placement of VE damping connections in the structure the deformation of connection

were reduced by an average of 64.41%.


0

2

4

6

8

10

12

14

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8


De

form

ati

on

(m

m)

UD

VE


deformation in connection

As can be seen from Fig. 6.11, the largest deformation of connections in the

undamped structure was obtained under the El Centro earthquake excitation. The

deformation experienced under the Northridge earthquake was lower. The lowest

deformation was achieved under the Kobe earthquake.

In terms of reduction in the deformation of connection, the best results were recorded

under the El Centro earthquake. The second greatest reduction in the peak values of

the deformation was achieved under the Kobe earthquake. The reduction in the

deformation of connections achieved under the Northridge was the lowest. In

general, the VE damping connections operated very well in all storeys and the range

of the results was very close.

Fig. 6.12 demonstrates that the maximum axial forces in the connections under the El

Centro earthquake, for the undamped structure were in the range 37.74 -261.49 kN.

With the placement of VE damping connections in the structure, the axial forces in

connections were reduced by an average of 72.29%. The results show that

considerably high efficiency of the VE damping connections was obtained in the

storey 1-16, however the efficiency of VE damping connections was lower in storeys

17 and 18.


171

The axial forces under the Kobe earthquake for the undamped structure oscillated in

the range 52.07-152.23 kN. However, with the introduction of VE damping

connections to the structure, the axial forces in connections were decreased by an

average of 68.68%. The maximum axial forces in connections under the Northridge

earthquake, for the undamped structure were in the range 37.52 -232.92 kN. While

with the placement of VE damping connections the axial forces were reduced by an

average of 64.45%.

As can be seen from Fig. 6.12, the largest forces in connections in the undamped

structure were achieved under the El Centro earthquake excitation. The axial forces

experienced under the Northridge earthquake were lower and the axial forces

obtained under the Kobe earthquake was the lowest. In terms of reduction of axial

forces in the connections, the best results were recorded under the El Centro

earthquake.

The second greatest reduction in the peak values of the axial forces was achieved

under the Kobe earthquake and reduction in the axial forces of connections achieved

under the Northridge earthquake was the lowest. In general, under all three selected

earthquake excitations, the decrease in axial forces was greater towards the highest

storeys; however the reduction in the axial forces in the top storey was considerably

lower compared to the storeys 1-17.


-20

10

40

70

100

130

160

190

220

250

280

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8


Fo

rce

(kN

)

UD

VE


force in connection


172

Fig.6.13 also shows that the maximum differential displacement between frame and

facade under the El Centro earthquake, for the undamped structure, oscillating in the

range 1.35- 13.36 mm. However, with the introduction of VE damping connections

to the structure, the differential displacement was reduced by an average of 77.33%.

The differential displacement under the Kobe earthquake fluctuated in the range

1.43- 7.8mm. When the VE damping connections were fitted a reduction of 69.54%

for upper and lower storeys was obtained. Reduction in the middle storeys obtained

was significantly lower. The maximum differential displacement under the

Northridge earthquake, for the undamped structure, was in the range 0.66 –

11.94mm. However, after the VE damping connections were fitted, the differential

displacement was reduced by an average of 71.71%.

It can be observed from Fig. 6.13, the largest differential displacement between

frame and facade in the undamped structure was obtained under the El Centro

earthquake excitations. Kobe demonstrated least displacement with Northridge

falling in between. In terms of reduction in the differential displacement between

frame and facade, the best results were recorded under the El Centro earthquake.

Reduction in the peak values of the differential displacement under the Northridge

earthquake was lower and reduction in the differential displacement achieved under

the Kobe earthquake was the lowest. In general the results showed that the VE

damping connections operated very well under all three selected earthquake

excitations and great reductions in the peak values of all investigated parameters

were achieved.


173


0

2

4

6

8

10

12

14

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8


Diff

ere

nti

al D

isp

lace

me

nt

(mm

)

UD

VE



Fig. 6.14 demonstrates that the maximum interstorey drifts under the El Centro

earthquake, for the undamped structure, were in the range 12.64-31.18 mm. However

with the insertion of VE damping connections in the structure, the maximum

interstorey drifts were reduced by an average of 75.66 %. The maximum interstorey

drifts under the Kobe earthquake, for the undamped structure, were in the range 6.98-

17.47 mm, whereas with the placement of VE damping connections, the interstorey

drifts were reduced by an average of 65.81%.

The maximum interstorey drifts under the Northridge earthquake, for the undamped

structure, were in the range 8.97- 28.27 mm. However, after the VE damping

connections were fitted, the interstorey drifts were reduced by an average of 70.70%.

As can be seen from these results, under all three selected earthquake excitations, the

decrease in interstorey drifts was normally increased towards the highest storeys, in

general however, the VE damping connections worked perfectly well in all storeys

and the range of the results was very close across all selected earthquakes. Fig. 6.14

illustrates that the largest interstorey drift in the undamped structure was obtained

under the El Centro earthquake excitations. Kobe demonstrated the least interstorey

drift with the Northridge earthquake falling in between.


174


-1258

1114172023262932

S1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18

S1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18

S1

-2S

.3-4

S.5

-6S

.7-8

S.9

-10

S.1

1-1

2S

.13-

14

S.1

5-1

6S

.17-

18


Inte

rsto

ery

Dri

ft (

mm

)

UN

VE

Figure 6.14 18-storey structure with and without VE damping connections,

maximum interstorey drifts

In terms of reduction in the interstorey drifts, the best results with the greatest

reduction were recorded under the El Centro earthquake. The next greatest reduction

in the peak values of the interstorey drifts was achieved under the Northridge

earthquake. The reduction in the interstorey drifts achieved under the Kobe was

lower than the Northridge and El Centro earthquakes.

Fig.6.15 also shows that the maximum distortion of facade for the undamped

structure under the El Centro earthquake for the middle and upper storeys oscillated

in the range 0.0018-0.0022 radian, while for figures for the lower storeys were

significantly less. However, with the introduction of VE damping connections, the

distortion of the facades was reduced by an average of 75.25%.

As can be seen in Fig. 6.15, distortion of the facade for the undamped structure under

the Kobe earthquake for middle and upper storeys oscillated in the range 0.0012-

0.0014 radian, while for lower storeys were significantly less. With the placement of

the VE damping connections in the structure, the distortion of the facades decreased

by an average of 57.88%. The maximum distortion of facades under the Northridge

earthquake, for the undamped structure was in the range 0.001148- 0.001918 radian.

On the other hand, after the VE damping connections were fitted in the structure the

distortion of the facades was reduced by an average of 71.62%. Generally from

these results, it can be stated that the VE damping connections under all three


175

selected earthquake excitations, confirmed high efficiency across all selected

earthquakes.


-1E-04

0.0002

0.0005

0.0008

0.0011

0.0014

0.0017

0.002

0.0023

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8S

.2S

.4S

.6S

.8S

.10

S.1

2S

.14

S.1

6S

.18

S.2

S.4

S.6

S.8

S.1

0S

.12

S.1

4S

.16

S.1

8

Kobe Northridge

Dis

tort

ion

(R

ad

ian

)UD

VE

Elcentro

Figure 6.15 18-storey structure with and without VE damping connections,

maximum distortion of facade

As Fig. 6.15 indicates, the largest distortion of the facade in the undamped structure

was obtained under the El Centro earthquake. The distortion experienced under the

Northridge earthquake was lower. The distortion of facade recorded for the Kobe

earthquake was the lowest. In terms of reduction in the distortion of facade, the best

results were produced under the El Centro earthquake. The reduction in the distortion

of facade achieved under the Northridge earthquake was slightly lower. The

reduction in the distortion of facade achieved under the Kobe earthquake was the

lowest.

The results clearly demonstrated that the undamped structure considering load case1,

provided larger values in all investigated parameters in comparison to load case 2,

however, the energy absorbing connections in building facade system were able to

control facade distortion reasonably well considering both load cases under the

chosen earthquake excitations.



connections considering load cases 1 (larger load) and 2 (smaller load), under the El

Centro, Kobe and Northridge earthquakes were investigated. The results from the


176

undamped structures for both load cases revealed high levels of the deformation and

axial forces in connections, differential displacement between facade and frame,

distortion of facade, and interstorey drift under the selected earthquake excitations.

The highest values on all the investigated parameters were experienced under the El

Centro earthquake. It was followed by the significantly high values obtained under

the Northridge earthquake. The values obtained under the Kobe earthquake were the

lowest.

Considering load case 1, overall results showed that under the El Centro and

Northridge earthquakes the integration of the VE damping connections to the


decreased the seismic effect on facade at all levels of the structure. However, the

performance of the energy absorbing connections in the upper levels provided better

mitigation of the seismic load than in the lower levels. Reduction in all investigated

parameters usually increased towards the uppermost storeys under both earthquake

excitations.

In contrast to the El Centro and Northridge earthquake, a surprisingly wide range of

results was produced under the Kobe earthquake when the magnitude of the

differential displacement between frame and facade was determined. The results

show that in storeys 1-10 and 14-18 a high level of efficiency was obtained through

the VE damping connections; however this was not the case in storeys 11-13, where

an increase in the differential displacement between frame and facade was recorded.

Similarly, in the case of the facade distortion, very high efficiency of the energy

absorbing connections was obtained across storeys 1-11 and 16-18. However in

storeys 12-15 the VE damping connections did not display the same level of

efficiency with an increase in distortion being recorded at these levels. Likewise, a

similar trend was observed while determining the interstorey drift of the 18-storey

structure. The results showed that in storeys 1-10 and 16-18 a high level of efficiency

was achieved with the VE damping connections; however this was not maintained in

storeys 11-15 where an increase in the interstorey drift was recorded. From the fig

6.14 it can be seen that this occurred due to small interstorey drift in these storeys.

The VE damping mechanism was ineffective when the interstorey drifts were very

small and were not able to activate the damper.


177





Considering load cases 2, the overall results showed that under the El Centro, Kobe

and Northridge earthquakes the incorporation of the VE damping connections to the

building facade systems provided a considerable improvement in the steadiness of

the energy absorption and reduced the seismic effect on facade at all levels of the

structure. However, the performance of the VE damping connections in the upper

levels provided better mitigation of the seismic effect than in the lower levels.

Reduction in all investigated parameters usually increased towards the uppermost

storeys under all three selected earthquake excitations.

Under load case1 (larger load), provided larger values in all investigated parameters

in comparison to those under load case 2 (smaller load), thus under both load cases

the undamped structure produced significantly high values for all the investigated

parameters. However, the connections properties developed in this research were

able to have favourable results even when the natural frequencies of the structure

were within the dominant frequencies of the earthquakes.


178


179

Chapter 7

Conclusions and Recommendations


180

7. Conclusions and Recommendations

7.1. Contribution from this research

This research project comprehensively investigated the seismic response of multi-

storey building facade systems and the influence of energy absorbing connections on

the response. The parameters treated in this project are (i) 4 structural models (3, 6,

12 and 18 storey buildings), (ii) 2 different load cases, (iii) 3 different earthquake

records, (iv) different connections properties (and optimum values) and (v) Facade

types and influence of mass. Initially, a 3 storey one bay structure was developed to

verify the correctness of the analysis procedure and to ensure that the required results

were achievable. After establishing the feasibility of the procedure and calibrating

the computer model, the influence of the energy absorbing connection was

investigated in three additional structural models, namely a 6-storey building facade

system model, a 12-storey building facade system model and an 18-storey building

facade system model. These structures were analysed under three different

earthquake events for two load cases, to investigate the influence of load magnitude.

Firstly, the effect of the connection stiffness on the seismic response of the structural

system was investigated. Later on the building facade system was fitted with the VE

damping connections and was reanalysed to investigate the effectiveness of energy

absorber connection. The effect of the facade mass as will as the facade material in

terms of precast concrete and glass were also important and key parameters of this

research.

A range of values for the facade connection properties with respect to stiffness and

energy absorption capability (or damping) which provide efficient seismic

performance of the facades were considered and eventually the optimum values for

the facade-connection properties were established and used. The development of this

research information will minimise facade failure during earthquakes. The main

findings of the present study are listed below:

� It is feasible to use energy absorbing connections in building facade system to

control facade deformation under seismic loads and minimise facade failure.

Viscoelastic dampers have proved to be very efficient for this purpose and the

connection properties have significant influence in the response. They have


181

optimum values of stiffness kd = 20,000 kN/m and damping Cd = 35,000

kNs/m. There properties have been shown to be close to those provided in the

theory of Abbas and Kelly (1993). Damping parameter Cd has a greater

influence than the stiffness parameter kd in the response.

� The energy absorbing connections were able to control the deformation and

forces in connections, differential displacement between frame and facade

and the distortion of facades reasonably well, for all the earthquakes treated

in this study.

� Influence of mass on the seismic mitigation was investigated. Results from

the undamped structure showed that increase in the mass ratio resulted in

higher average percentage reductions in differential displacement. However,

for the damped structure increase in the mass ratio up to 15% resulted in the

increase of average percentage reduction in differential displacement

followed by smaller reductions in this parameter at higher mass ratios.

� The energy absorbing connections were able to reduce the high stresses in

glass panels to acceptable values and thereby prevent breaking of the panels.

� Seismic mitigation of the building facade system was possible even when the

natural frequencies of the structure were within the range of dominant

frequencies of the earthquakes.

� In addition to controlling facade response, the energy absorbing connections

were able to exert some control on the overall structure as well.

This thesis presents optimum mitigation of facade deformation with VE damping

connections. However as evident from the result presented dampers with smaller

values of spring stiffness (kd) and dashpot damping (Cd ) and hence smaller in size

will also provide effective control depending on what is required. The results showed

that the best performance of VE damping connections in most cases was observed to

be achieved in the upper storeys in comparison to the lower and middle storeys.

Some cases in the 18-storey structure under the Kobe earthquake excitations the VE

damping connections in the upper storeys were not effective at all, as in those storey

levels, an increase in the magnitude of the parameters were noted. This can be

explained by the fact that the Kobe earthquake had an unusually low dominant

frequency range.


182

7.1.1. 3-storey building facade system

The use of energy absorbing connections (damping devices) to mitigate the seismic

effect on a simple three storey building facade system was first investigated in this

study. The results showed that the connection properties had significant influence on

seismic response of building facade system. The optimum values for spring stiffness

and dashpot damping were found as kd = 20,000 kN/m and Cd =35,000 kNs/m

respectively. The closer investigation of the three storey structure showed that the

effectiveness of the energy absorbing connectors varied under the different

earthquake events. This can be attributed to the varying intensity and frequency

content of the earthquake. The results of the study indicated that an increase in the

stiffness of spring did not have an influence in controlling the behaviour of the

facade. However an increase in the dashpot damping value up to the optimum value

has shown to have an important role in reducing values in all parameters. Beyond

this value, the response of the seismic loading on the structure, started to increase.

From the several time history analyses carried out, it was evident that with the

implementation of appropriate connection properties, the differential displacement

between the facade and the frame and the facade distortion can be considerably

reduced. Moreover the connection deformation and the connection forces can be kept

within reasonable and practical limits. From the results it is also evident that

incorporation of facade in the frame system played an important role in altering inter-

storey drift. Results have shown that the connection stiffness and energy absorption

capacity have a great influence in mitigating the adverse effects of earthquakes. The

feasibility of the computer analysis procedure was established and the computer

model was calibrated. The study has indicated the possibility of developing

connections with appropriate properties so as to minimise facade failure during

earthquakes. Detail of the implementations are given below

7.1.1.1. Implementation of the procedure

i. Design the building as for normal case under gravity loads, and wind load if

necessary

ii. Decide on the type of façade and obtain its property

iii. Carry out free vibration analysis (fundamental frequencies of the structure)


183

iv. Use the information to determine suitable properties of the VE damper as

discussed in chapter 3

v. Check the size of the connections

vi. Install the VE damper and analyse under earthquake and check the

performance

vii. Check the response in terms of the desired response parameters such as inter

storey drift, distortion of facade and differential displacement etc. check if

they are satisfied, if not change the damper property and analyse (go to step

iv) till the desire response is obtained.



connections considering 2 separate load cases 1 and 2, under the El Centro, Kobe and

Northridge earthquakes were investigated. The results from the undamped structures

revealed high levels of the deformation and axial forces in connections, differential

displacement between facade and frame, distortion of facade, and interstorey drift

under the selected earthquake excitations. The largest values for all the investigated

parameters under the load case 1 (larger load), were experienced under the

Northridge earthquake. It was followed by the significantly high values obtained

under the Kobe earthquake. The values obtained under the El Centro earthquake

were the lowest. Considering load case 2 (smaller load), similarly the largest values

for all the investigated parameters were experienced under the Northridge

earthquake. The values obtained under the Kobe earthquakes were very close to

those of the Northridge. The El Centro earthquake yet again produced the lowest

values for all the investigated parameters.


building facade systems enhanced the effectiveness of the energy absorption and

decreased the seismic effect on facade at the all levels of the structure. However, the

performance of the VE damping connections in the upper levels provided better

seismic mitigation than in the lower levels. Reduction in all investigated parameters

usually increased towards the uppermost storeys under all three earthquake

excitations.


184

Considering load cases 1 and 2, the results showed that the greatest average



Kobe earthquake excitation, which was characterised by a strongly narrow dominant

frequency range (0.29-1.12 Hz). The second highest average deflection reduction

occurred under the Northridge earthquake, which had a strongly dominant narrow

frequency range (0.14-1.07 Hz). In the case of the El Centro earthquake excitation,

which exhibit a wide band of dominant frequencies (0.39-6.39Hz), the efficiency of

the VE damping connections was slightly lower, probably because the natural

frequency of the structure was within this band.

Load case1 (larger load), provided larger values in all investigated parameters in

comparison to those under load case 2 (smaller load). However, the energy absorbing

connections in building facade system were able to control facade distortion

reasonably well considering both load cases under the chosen earthquake excitations.





Increase in the facade mass under the Kobe earthquake, gave a complex response on

the deformation of connections, distortion of facade, differential displacement

between frame and facade and interstorey drift. However, under the El Centro and

Northridge earthquake excitations, an increase in the facade mass displayed a very

little effect in all investigated parameters.

The connections properties developed in this research are able to have favourable

results even when the natural frequencies of the structure are within the dominant

frequencies of the earthquakes.



connections considering load cases 1 and 2, under the El Centro, Kobe and

Northridge earthquakes were investigated. The structures fitted with precast concrete

facades were investigated considering load case 1 and 2, under all three selected


185

earthquake excitations, while the structures fitted with glass facades were

investigated considering case 1, under the El Centro earthquake excitation.

In general, the results from the undamped structures once again revealed high levels

of the deformation and axial forces in connections, differential displacement between

facade and frame, distortion of facade, and interstorey drifts under the selected

earthquake excitations. Considering load case 1, the largest values for all the

investigated parameters, in the structure fitted with precast concrete facade were

experienced under the El Centro earthquake. It was followed by the significantly

high values obtained under the Northridge earthquake. The values obtained under the

Kobe earthquake were the lowest. Considering load case 2, the biggest values for all

the investigated parameters occurred under the Northridge earthquake. It was

followed by the notably high values obtained under the Kobe earthquake. The values

obtained under the El Centro earthquake were the lowest.

The results from the undamped structure showed that in most cases, the vertical load

had a significant affect on the behaviour of the building facade system. The structure

under the larger load case (Case 1) has produced larger values in response compare

to the smaller load case (Case 2), when subjected to El Centro and Northridge

earthquake excitations. In the case of the Kobe earthquake the response values

produced under both load cases were approximately the same.

The overall results showed that the incorporation of the VE damping connections to

the building facade systems enhanced the reliability of the energy absorption and

decreased the seismic effect on facade at the all level of the structure. However,

while considering load case 1, the performance of the VE damping connections in

the upper levels provided better mitigation of the seismic load than in the lower

levels. Reduction in all investigated parameters usually increased towards the

uppermost storeys under all three earthquake excitations. Considering load case 2,

while investigating the deformation and forces in connections, the result revealed a

better performance of the VE damping connections in the middle levels, providing

better mitigation of the seismic load than in the lower and upper levels. In the case of

the differential displacement between frame and facade, distortion of facades and

interstorey drift, the VE damping connections provided better mitigation of the

seismic load in the upper storeys than the lower storeys.


186

Considering load case 1 (larger load), the results showed that the greatest average


between facade and frame, and the distortion of facade was experienced under the El

Centro earthquake excitation, which exhibit a wide band of dominant frequencies

(0.39-6.39Hz). The second highest average deflection reduction occurred under the

Northridge earthquake, which had a strongly dominant narrow frequency range

(0.14-1.07 Hz). In the case of the, Kobe earthquake excitation, which was

characterised by a strongly narrow dominant frequency range (0.29-1.12 Hz) the

efficiency of the VE damping connections was slightly lower. The behaviour of the

structure under the all three earthquakes demonstrated the complex behaviour of the

building facade system under seismic loads.

In terms of the reduction of deformation and axial forces in connections, differential

displacement between frame and facade and distortion of the facade under the El

Centro, Kobe and Northridge earthquake excitations in the second storey level across

the width of the structure (horizontal direction), the results obtained were very close.

Considering load case 2 (smaller load), the results showed that the greatest average



Kobe earthquake excitation, The second highest average reduction occurred under

the Northridge earthquake, while in the case of the El Centro earthquake, the

efficiency of the VE damping connections was slightly lower. Similar for load case

1, the results for load case 2 displayed a complex behaviour of the building facade

system under the all three earthquakes.

The application of selected earthquake records scaled to a PGA of 0.5g had

significant effects on the seismic response of building facade system, as larger values

in response for all investigated parameters occurred compared to those under

earthquake records scaled to a PGA of 0.2g. However the energy absorbing

connections were able to control the deformation and forces in connections,

differential displacement between frame and facade and the distortion of facades

reasonably effectively.


187

Influence of mass on the seismic mitigation was investigated. Results from the

undamped structure showed that increase in the mass ratio resulted in higher average

percentage reductions in differential displacement. However, for the damped

structure increase in the mass ratio up to 15% resulted in the increase of average

percentage reduction in differential displacement followed by smaller reductions in

this parameter at higher mass ratios.

In terms of the structure fitted with glass facade the undamped structure experienced

significantly high levels of the deformation and axial forces in connections,


interstorey drift under the selected earthquake excitations. Overall, the insertion of

the VE damping connections in the structure provided significant reductions in all

investigated parameters. The efficiency of the energy absorbing connections while

considering the deformation and force in connections was similar across all storeys.

However, considering the differential displacement between frame and facade,

interstorey drift and the differential displacement between upper and lower facades,

the VE damping connections provided better performance in the lower storeys in

contrast to the upper and middle storeys. The results also demonstrated that the

effectiveness of the VE damping connections for storeys 10 and 11 was insignificant.

A very small increase in displacement was recorded at these levels. This can be

explained by the fact that the natural frequency of the 12 story building is within the

frequency of dominant motions of the El Centro earthquake. The stresses found in

the glass panel in the undamped structure were significantly high; however with the

insertion of the VE damping connections, the maximum stress in the glass panel was

reduced to an acceptable limit in which the panel will not break.



connections considering load cases 1 (larger load) and 2 (smaller load), under the El

Centro, Kobe and Northridge earthquakes were investigated. The results from the

undamped structures for both load cases revealed high levels of the deformation and

axial forces in connections, differential displacement between facade and frame,

distortion of facade, and interstorey drift under the selected earthquake excitations.

The highest values on all the investigated parameters were experienced under the El


188

Centro earthquake. It was followed by the significantly high values obtained under

the Northridge earthquake. The values obtained under the Kobe earthquake were the

lowest.

Considering load case 1, overall results showed that under the El Centro and

Northridge earthquakes the integration of the VE damping connections to the


decreased the seismic effect on facade at all levels of the structure. However, the

performance of the energy absorbing connections in the upper levels provided better

mitigation of the seismic load than in the lower levels. Reduction in all investigated

parameters usually increased towards the uppermost storeys under both earthquake

excitations.

In contrast to the El Centro and Northridge earthquake, a wide range of results was

surprisingly produced under the Kobe earthquake when the magnitude of the

differential displacement between frame and facade was determined. The results

show that in storeys 1-10 and 14-18 a high level of efficiency was obtained through

the VE damping connections; however this was not the case in storeys 11-13, where

an increase in the differential displacement between frame and facade was recorded.

Similarly, in the case of the facade distortion, very high efficiency of the energy

absorbing connections was obtained across storeys 1-11 and 16-18. However in

storeys 12-15 the VE damping connections did not display the same level of

efficiency with an increase in distortion being recorded at these levels. Likewise, a

similar trend was observed while determining the interstorey drift of the 18-storey

structure. The results showed that in storeys 1-10 and 16-18 a high level of efficiency

was achieved with the VE damping connections; however this was not maintained in

storeys 11-15 where an increase in the interstorey drift was recorded. From the

results it can be stated that the interstorey drift in these storeys were very small in the

undamped structure. The VE damping mechanism was ineffective when the

interstorey drifts were very small and were not able to activate the damper.






189

Considering load cases 2, the overall results showed that under the El Centro, Kobe

and Northridge earthquakes the incorporation of the VE damping connections to the

building facade systems provided a considerable improvement in the steadiness of

the energy absorption and reduced the seismic effect on facade at all levels of the

structure. However, the performance of the VE damping connections in the upper

levels provided better mitigation of the seismic effect than in the lower levels.

Reduction in all investigated parameters usually increased towards the uppermost

storeys under all three selected earthquake excitations.

Under load case1 (larger load), provided larger values in all investigated parameters

in comparison to those under load case 2 (smaller load), thus under both load cases

the undamped structure produced significantly high values for all the investigated

parameters. However, the connections properties developed in this research were

able to have favourable results even when the natural frequencies of the structure

were within the dominant frequencies of the earthquakes.

7.1.5. Conclusion

A 3-storeys, 6-storeys, 12-storeys and 18-storeys building facade system with and

without energy absorbing connections were investigated under three different

earthquake records. Each of these building facade systems with energy absorbing

connections behaved in a different manner, and the effectiveness of the energy

absorbing connections varied under the different earthquake records. This can be

attributed to the varying intensity and frequency content of the earthquakes.

However, some specific features can be observed. The VE damping connections in

the majority of cases were able to produce remarkably high improvement and

reduced the seismic effect on facades at all levels of the structure. The best

performance of VE damping connections in most cases was observed to be achieved

in the upper storeys in comparison to the lower and middle storeys. On the contrary,

in some cases under the Kobe earthquake excitations the VE damping connections in

the upper storeys were not effective at all, as in those storey levels, an increase in the

magnitude of the parameters were noted. In addition, the undamped structures

revealed the highest levels of the deformation and axial forces in connections,



190

interstorey drifts under the selected earthquake excitations at lower storeys under

both load cases. Similarly the performances of the VE damping connections at those

storeys were less favourable.


building facade systems enhanced the effectiveness of the energy absorption and

decreased the seismic effect on the all level of the structure.

A number of different structure types inserted with energy absorbing connections and

treated under different earthquake excitations were carried out to achieve a

comprehensive understanding of the efficiency of the VE damping connections. This

study treated the behaviour of building facade system under a range of seismic

excitations even when the dominant seismic frequencies coordinated the natural

frequency of the structure. It has been revealed that it is possible to have seismic

mitigation, under all earthquake excitations, by using VE damping connections and

to control facade deformation.

7.2. Recommendations for further research

The following are suggestions for further research in this area:

i. Investigation of behaviour of the building facade system integrated with other

type of energy absorbing connections.

ii. Investigation of behaviour of the building facade system integrated with

energy absorbing connections under other earthquake excitations with a wide

range of frequencies and peak ground accelerations.


191

List of References

Abbas, H. and Kelly, J. M., (1993), “A Methodology for Design of Viscoelastic Dampers in Earthquake-Resistant Structures,” Report No. UCB/EERC 93/09, Earthquake Engineering Research Center, University of California at Berkeley, Berkeley, CA.

Anicic, D., Zamolo, M. and Soric, Z., (1980), "Experiments on Non-Structural Partition Walls Exposed to Seismic Forces," Proceedings, Seventh World Conference on Earthquake Engineering, Istanbul, Turkey, September 8-13, Vol. 6, pp. 144-150.

Arnold, C., (1989), "Cladding Design: Recent Architectural Trends and Their Impact on Seismic Design," Proceedings, International Symposium on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, held in Chicago, Illinois, Nov. 89, pp. 14-31.

AEES, Newsletter, www.aees.org.au/Socity/Constitution.htmi-6k-18 Sept. 2002.

Australian / New Zealand Standard AS/NZS 1170.1: 2002. Structural design actions, Part 1: Permanent, imposed and other actions.

Bergman, D. M. and Hanson, R. D., (1988), "Characteristics of Mechanical Dampers," Proceedings, Ninth World Conference on Earthquake Engineering, Tokyo and Kyoto, Japan, August 2-9, Vol. VI , pp. 33-38.

Behr A. R., Belarbi A. and Culp, J.H., (1995),” Dynamic Racking Tests of Curtain Wall Glass Elements with In-plane stress and Out-of-plane stress Motions.” Earthquake Engineering and Structural Dynamics, vol. 24, pp.1-24.

Bozorgnia, Y., Campbell, K.W.,(2004), " The Vertical- to –horizontal response spectral ratio and tentative procedures for developing simplified V/H and vertical design spectra” Earthquake Eng., 8(2), 175-

Bozorgnia, Y., Mahin, S.A. and Bradley, A.G. (1998), " Vertical response of twelve structures recorded during the Northridge earthquake” Earthquake Spectra, 14(3), 411-432

Charney, F. and Harris, J. R., (1989), " The Effect of Architectural Precast Concrete Cladding on the Lateral Response of Multistorey Buildings," Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 80-96.

Charney, Finley A. and Harris, James R., (1989), “The Effect of Architectural Precast Concrete Cladding on the Lateral Response of Multistory Buildings.” Proceedings: Architectural Precast Concrete Cladding – its Contribution to Lateral Resistance of Buildings. PCI, November 8-9, Chicago, pp. 83 -94.


192

Cohen, J. M. and Powell, G. H., (1991),"A Preliminary Study on Energy Dissipating Cladding-Frame Connections," Report No. UCB/EERC-91/09, EERC, University of California, Berkeley, California, September, 73 pages.

Cohen, J. M. and Powell, G. H., (1993), "A Design Study of an Energy-Dissipating Cladding System," Earthquake Engineering and Structural Dynamics, vol. 22, pp. 617-632.

Craig, J., Goodno, B., Pinelli, J. & Moor, C.,(1992), "Modelling and Evaluation of Ductile Cladding Connection Systems for Seismic Response Attenuation in Buildings," Proceedings, 10th World Conference on Earthquake Engineering, July 19-24, Madrid, Spain, vol 7, pp.4183-4188.

Chung, K. C., Soong, T. T., Oh, S. T. and Lai, M. L., (1995), “Seismic Behaviour of Steel Frame with Added Viscoelastic Dampers,” Journal of Structural Engineering, 121(10), pp.1418-1426.

Cladding Research Institute (1995), “Literature Review on Seismic Performance of Building Cladding Systems”, NIST GCR 95-681,179 p Emeryville, California February Dowrick, D.J., (1977), “A Manual for Engineers and Architects” Earthquake Resistant Design.

Earthquake Hazards Program, “USGS Earthquake Information for 2006”, www.usgs.gov.

Facades: Errors Can Be Expensive, Engineering-News Record, Vol 204, No. 5, January 24, 1980, pp. 30-34.

Foutch, D. A., Wood, S. L. and Brady, P. A., (1993), “Seismic Retrofit of Non-ductile Reinforced Concrete Using Viscoelastic Dampers,” ATC-17-1 Seminar on Seismic Isolation, Passive Energy Dissipation, and Active Control, San Francisco, CA, 605-616.

Freeman, S. A., (1989), Participation of Architectural Precast Concrete Cladding in Resisting Lateral Forces in Regions of High Seismicity," Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 32-35.

G. James Glass and Aluminium Pty Ltd, 2003, Brisbane Australia.

Gjelsvik, A., (1974),"Frames and Precast Panels Walls," J. of the Structure. Div., ASCE, Vol 100, No ST2, February, pp.405-426.

Gjelvik, A., (1973), “Interaction between Frames and Precast Panel Walls,” J. of the Structure. Div., American Society of Civil Engineering (ASCE), Vol 100, No (ST2), Feb, pp.405-426.

Grigorian, C. E., Yang, T., and Popov, E. P., (1993). “Slotted Bolted Connection Energy Dissipators,” Earthquake Spectra, 9(3), 491-504.

Goodno, B., Craig, J., El-Gazairly, L. & Hsu, C-C, (1992), "Use of Advanced Cladding Systems for Passive Control of Buildings Response in Earthquakes,"


193

Proceedings, 10th World Conference on Earthquake. Engineering, July 19-24, Madrid, Spain, vol7, pp.4195-4200.

Goodno, B.J., Craig, J.I., Meyyappa, M., and Palsson, H., (1983),"Cladding-Structure Interaction in High-rise Buildings," Final Report, NSF Grant No. CEE-7704269, (NTIS Report No. PB83-195891), January, 614 pages.

Goodno, B.J. and Palsson, H., (1981), “Torsional Response of Partially Facade Structures,” Proc., Conf. on Earthquakes and Earthquake Engineering, September, pp. 859- 877.

Goodno, B. J., Craig, J. I., Dogan, T., and Towashiraporn, P., (1998), "Ductile Cladding Connection Systems for Seismic Design," Georgia Institute of Technology NIST GCR 98-758.

Goodno, B.J. and Craig, J.I. (1989), “Historical Overview of Studies on the Contribution of Cladding to Lateral Resistance of Buildings,” Proc. Architectural Precast Concrete Cladding and its Contribution to Lateral Resistance of Buildings, PCI, Chicago, Illinois, Nov 89, pp. 36-47.

Hegle, R. L., (1989),"Connection of Cladding to Multi-Story Structures,’ Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, held in Chicago, Illinois, Nov. 8-9, pp. 192-201.

Hamburger, R.O., (1997), “A Framework for Performance Based Earthquake Resistive Design” NISEE National Information Service for Earthquake Engineering, university of California, Berkeley http://nisee.berkeley.edu/lessons/hamburger.html.

Iverson, J. K., (1986), "Concrete Cladding Connections in Earthquake Country," Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 202-216.

Kallros, M. K., (1987),"An Experimental Investigation of the Behaviour of Connections in Thin Precast Concrete Panels under Earthquake Loading," Master Thesis, Department of Civil Engineering, University of British Columbia, Vancouver, Canada, April, 214 pages.

Kemeny, Z., and Lorant, J., "Energy Dissipating Elastomeric Connections," Proceedings, International Symposium on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, held in Chicago, Illinois, Nov. 8-9, 1989, pp. 287-299.

Krawinkler, H (1999), “Advancing Performance- Based Earthquake Engineering”, Stanford University, http://peer.berkeley.edu/news/1999jan/advance.html

Madsen, L.P.B., (2001), “Controlling the Seismic Response of Structures by the Use of Dampers in Shear Walls”, Master Thesis, School of Civil Engineering, Queensland University of Technology, Brisbane, Australia,179 Pages.


194

Mahmoodi, P., (1969),"Structural Dampers," Journal of Structural Engineering, ASCE, Vol. 95, No. ST8, Paper 6725, August, pp. 1661-1672.

Marko, J., (2006), “Study of Viscoelastic and Friction Damper Configurations in the Seismic Mitigation of Medium-Rise Structures” Journal of Mechanics of Materials and Structures, Accepted in April 2006 for Publication in 2006.

McCue, G.M., et al., (1975),"Building Enclosure and Finish Systems, Their Interaction with the Primary Structure during Seismic Action," Proceedings, U.S. National Conference on Earthquake Engineering, Michigan, June 18-20, pp. 235-244.

McCue, G.M., Skaff, A. and Boyce, J., (1978), "Architectural Design of Building Components for Earthquakes," MBT Associates, San Francisco, California.

Memari, A.M., Manntes, H. and Bozorgnia, Y., (2004)"Study of the Effect of Near-Source Vertical Ground Motion on Seismic Design of Precast Concrete Cladding Panels" Journal of Architectural Engineering ASCE, December

Min, K.W., Kim, J. and Lee, S.H., (2004), “Vibration Tests of 5-storey Steel Frame with Viscoelastic Dampers,” Engineering Structures, 26, May, pp. 831-839.

Moor, C., (1992), "Analytical and Experimental Evaluation of Advanced Cladding Connections," Master Thesis, School of Civil Engineering, Georgia Institute of Technology, Atlanta, Georgia, April, 123 pp.

Oppenheim, I.J., (1973),"Dynamic Behaviour of Tall Buildings with Cladding," Proceedings, Fifth World Conference on Earthquake Engineering, Rome, Italy, June, pp. 2769-2773.

Pall, A. S., and March, C., "Optimum Seismic Resistance of Large Panel Structures Using Limited Slip Bolted Joints," Proceedings, Seventh World Conference on Earthquake Engineering, Istambul, Turkey, September 3-13, 1980, Vol 4, pp. 177-184.

Pall, A. S., (1989), "Friction Damped Connections for Precast Concrete Cladding," Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 300-310.

Palsson, H., and Goodno, B. J., "A Degrading Stiffness Model for Precast Concrete Cladding," Proceedings, Seventh European Conference on Earthquake Engineering, Athens, Greece, September 20-25, 1982.

PCI Manual on Design and Typical Details of Connections for Precast and Prestressed Concrete, Second Edition, Prestressed Concrete Institute, 175 W., Jackson Blvd., Chicago, Illinois 60604, 1988.

PCI Design Handbook: Precast and Prestressed Concrete, Third Edition, Prestressed Concrete Institute, Chicago, Illinois, 1985.


195

Pinelli, J.P., Craig, J.I., Goodno, B.J. and Hsu, C.C. (1993a), “Passive Control of Building Response Using Energy Dissipating Cladding Connections,” Earthquake. Spectra, Theme Issue Passive Energy Dissipation, EERI, 9(3), August, pp. 529-546.

Pinelli, J.P., Craig, J.I., Goodno, B.J. and Hsu, C.C. (1993b), “Response to J.M. Cohen’s ‘Discussion of Passive Control of Building Response Using Energy Dissipating Cladding Connections,’” Earthquake. Spectra, EERI, 10(2): May, pp. 447-449.

Pinelli, J-P., (1992),"Development of Energy Dissipating Cladding Connections for Passive Control of Building Seismic Response" Ph.D. Thesis, School of Civil Engineering, Georgia Institute of Technology, Georgia, November.

Pinelli, Jean-Paul, Craig, J. I. and Goodno, B. J., (1990),"Development of Advanced Concepts for Precast Cladding," Proceedings, ATC-29 Seminar, Seismic Design and Performance of Equipment and Non-structural Elements in Buildings and Industrial Structures, Irvine, California, October 3-4, pp. 26.1-26.11.

Pinelli, J.-P., and Craig J.I., "Experimental Studies of the Performance of Mexican Precast Cladding Connections," Proceedings, Int'l. Sump. on Architectural Precast Concrete Cladding, Precast/Prestressed Concrete Institute, Chicago, IL, November 8-9, 1989, pp.159-176.

Pinelli, J.-P., Moor, C., Craig, J. I. & Goodno, B. J., (1992),"Experimental Testing of Ductile Cladding Connections for Building Facades," International Journal of the Structural Design of Tall Buildings, John Wiley and Sons, Inc., Vol. 1, No. 1, October, pp. 57-72.

Pinelli, J-P. Craig, J.I., Goodno, B.J. and Hsu, C-C. (1993), "Passive Control of Building Response Using Energy Dissipating Cladding Connections," Earthquake Spectra, EERI, Vol. 9, No. 3, August, pp. 529-546.

Pinelli, J.P. Craig, J. I. and Goodno, B. J., (1995), "Energy-Based Seismic Design of Ductile Cladding Systems," Journal of Structural Engineering, vol. 121, pp. 567 - 578.

Pinelli, J.P. Moor, C., Craig, J. I. and Goodno, B. J., (1996), "Testing of Energy Dissipating Cladding Connections," Earthquake Engineering and Structural Dynamics, vol. 25, pp. 129-147.

Recommended Practice, Precast Concrete Facade Connection (1991), Concrete Institute of Australia.

Rihal, S. S., (1989), "Earthquake Resistance and Behaviour of Architectural Precast Cladding and Connections," Proceedings: Architectural Precast Concrete Cladding-Its Contribution to Lateral Resistance of Buildings, pp. 110-117.

Rihal, S. S., (1988), "Earthquake Resistance and Behaviour of Heavy Facades/Claddings and Connections in Medium-Rise Steel-Framed Buildings," Proceedings, Ninth World Conference on Earthquake Engineering, Tokyo, Japan, August 2-9, Vol. VI, pp. 207-212.


196

Rihal, S. S., (1988),"Seismic Behaviour and Design of precast Facades, Cladding and Connections in Low and Medium-Rise Buildings," Report ARCE R88-1, California Institute of Technology, November.

Sack, R. L., et al., (1981),"Seismic Behaviour of Precast Curtain Walls in High-rise Buildings," Final Report, NSF Grant No. PFR-7720884, Department of Civil Engineering, University of Idaho, Moscow, Idaho, January, 328 pp.

Sack, R. L., Beers, R. J., Thomas, D. L., (1989),"Seismic Behaviour of Architectural Precast Concrete Cladding," Proceedings, International Symposium on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 141-158.

Seike, Tsuyoshi, and Sakamoto, I. (1997). “A Report on the Damages of Precast Concrete Curtain Walls by the 1995 Hyogo-ken Nanbu Earthquake.” Proceedings of the International Conference on Building Envelope Systems and Technology, UK.

Smith, Bryan S. and Gaiotti, Regina (1989), Proceedings, Architectural Precast Concrete Cladding – Its Contribution to Lateral Resistance of Buildings. PCI, November 8-9, Chicago. pp. 48 - 60.

Soong, T. T. and Dargush, G. F., (1997), “Passive Energy Dissipation Systems in Structural Engineering”, John-Wiley & Sons, New York, NY.

Spronken, J. R., (1989), "Detailing of Cladding for Deformations," Proceedings, International Conference on Architectural Precast Concrete Cladding - Its Contribution to Lateral resistance of Buildings, Chicago, Illinois, Nov. 8-9, pp. 184-, J. 191.

Stockbridge G., "Experimental Methods for Evaluating the Condition of Facades to resist Seismic Forces," Proceedings, Eighth World Conference on Earthquake Engineering, San Francisco, California, July 21-28, 1984, Vol. VI, pp. 71-78.

Suter, G.T. and Hall, J.S., (1977), "How Safe Are Our Cladding Connections?" Proceedings, First Canadian Masonry Symposium, University of Calgary, Alberta, Canada, June 7-10, 1976. By Means of PTFE Sliding Joints," Bulletin of the New Zealand Society for Earthquake Engineering, Vol.10, No 3, September.

Tyler, R.G., "A Tenacious Base Isolation System Using Round Steel Bars," Bulletin of the New Zealand Society for Earthquake Engineering, Vol.11, No 4, pp. 273-281, December 1978.

Towashiraporn, P., Park, J., Goodna, B. J., and Carig, J.I. (2002) “Passive control methods for seismic response modification,” Journal of Progress in Structural Engineering and Material, 4, PP 74-86.

Wang, Marcy Li., (1986),"Full Scale Test of Cladding Components," Proceedings, Third Conference on Dynamic Response of Structures, UCLA, Los Angeles, California, March 31-April 2, pp. 495-504.

Weidlinger, P. (1973), “Shear Field Panel Bracing”, ASCE, 99(ST7), pp.1615-1631.


197

Whittaker, A., Aiken, I., Bergman, D. M., Clark, P., Cohen, J., Kelly, J. M., and Scholl, R., (1993), “Code Requirements for the Design and Implementation of Passive Energy Dissipation,” ATC-17-1 Seminar on Seismic Isolation, Passive Energy Dissipation, and Active Control, San Francisco, CA, 497-508.

Wilkinson, S. at al., (1997), “Simplified analysis of asymmetric buildings subjected to earthquakes” PhD Thesis, Queensland University of Technology. School of Civil Engineering.

Wulfert, H. and Behar, R.A. (1998), “Earthquake-Immune Curtain Wall System” United States Patent Application Serial Number 09/093,454, Filed June 8, 1998


198


199

Appendix A

Seismic responses of 3 storey building facade system

Table A.1: 3-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections.

Earthquakes Storeys UN VE % ReductionS.2 3.12 0.72 76.9

S.3 1.39 0.25 82.0

S.2 4.65 0.96 79.4

S.3 1.83 0.34 81.4

S.2 3.21 0.96 70.1

S.3 1.44 0.34 76.4

El-Centro

Kobe

Northridge

Table A.2: 3-Storey Building Facade System, Axial forces in connections (kN) for UN structure and structure with VE damping connections.


S.3 27.83 5.00 82.03

S.2 93.11 19.20 79.38

S.3 36.66 6.80 81.45

S.2 64.34 19.20 70.16

S.3 28.89 6.80 76.46

El-Centro

Kobe

Northridge

Table A.3: 3-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections.


S.3 1.42 0.25 82.39

S.2 4.88 1.00 79.51

S.3 1.87 0.34 81.82

S.2 3.34 1.00 70.06

S.3 1.48 0.34 77.03

Kobe

Northridge

El-Centro


200

Table A.4: 3-Storey Building Facade System, Distortion of facades (radian) for UN structure and structure with VE damping connections.

Earthquakes Storeys UN VE % ReductionS.2 4.18E-04 5.75E-05 86.2

S.3 2.18E-04 2.75E-05 87.4

S.2 6.10E-04 7.50E-05 87.7

S.3 2.90E-04 3.75E-05 87.1

S.2 4.25E-04 7.50E-05 82.4

S.3 2.30E-04 3.75E-05 83.7

El-Centro

Kobe

Northridge


201

Appendix B


Table B.1: 6-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 4.47 1.22 72.76 5.33 1.13 78.86 7.15 1.73 75.76S.3 3.56 0.79 77.81 3.72 0.72 80.68 5.54 1.10 80.15S.4 3.13 0.58 81.40 3.12 0.51 83.55 4.54 0.79 82.57S.5 2.22 0.35 84.02 2.50 0.31 87.64 2.99 0.48 83.84S.6 1.04 0.15 85.96 1.25 0.13 89.82 1.38 0.20 85.45

Kobe NorthridgeEl-CentroStoreys

Table B.2: 6-Storey Building Facade System, Axial forces in connections (kN) for UN structure and structure with VE damping connections.


El-Centro Kobe NorthridgeStoreys

Table B.3: 6-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections.


StoreysEl-Centro Kobe Northridge

Table B.4: 6-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 3.53E-04 9.09E-05 74.23 4.05E-04 8.30E-05 79.49 5.54E-04 1.29E-04 76.69S.3 3.07E-04 7.05E-05 77.07 3.18E-04 5.91E-05 81.43 4.83E-04 9.38E-05 80.60S.4 2.89E-04 5.68E-05 80.35 2.73E-04 4.77E-05 82.50 4.56E-04 7.50E-05 83.55S.5 2.44E-04 4.55E-05 81.34 2.27E-04 3.64E-05 84.00 3.67E-04 6.04E-05 83.52S.6 1.75E-04 2.95E-05 83.16 1.82E-04 2.50E-05 86.25 2.54E-04 3.96E-05 84.43



202

Table B.5: 6-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections, considering horizontal (X) direction.

UN VE % Reduction UN VE % Reduction UN VE % Reduction1.C-R 4.47 1.22 72.76 5.32 1.13 78.80 7.15 1.73 75.762.C-L 4.43 1.21 72.69 5.28 1.12 78.81 7.08 1.72 75.742.C-R 4.54 1.23 72.95 5.40 1.14 78.85 7.26 1.76 75.773.C-L 4.50 1.22 72.93 5.35 1.13 78.91 7.19 1.74 75.783.C-R 4.50 1.22 72.93 5.35 1.13 78.91 7.19 1.74 75.784.C-L 4.54 1.23 72.95 5.40 1.14 78.85 7.26 1.76 75.774.C-R 4.43 1.21 72.69 5.28 1.12 78.81 7.08 1.72 75.745.C-L 4.47 1.22 72.76 5.32 1.13 78.80 7.15 1.73 75.76

El-Centro Kobe NorthridgeBay Notation

Table B.6: 6-Storey Building Facade System, Axial force (kN) in connections for UN structure and structure with VE damping connections, considering X direction.


Bay Notation


Table B.7: 6-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections, considering X direction.


Bay Notation

Kobe NorthridgeEl-Centro

Table B.8: 6-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections, considering X direction.

UN VE % Reduction UN VE % Reduction UN VE % Reduction1-Sp 3.53E-04 9.09E-05 74.23 4.05E-04 8.30E-05 79.49 5.54E-04 1.29E-04 76.692-Sp 3.03E-04 7.27E-05 75.98 3.61E-04 7.39E-05 79.56 4.79E-04 1.15E-04 76.093-Sp 3.03E-04 7.27E-05 75.98 3.61E-04 7.39E-05 79.56 4.79E-04 1.15E-04 76.094-Sp 3.53E-04 9.09E-05 74.23 4.05E-04 8.30E-05 79.49 5.54E-04 1.29E-04 76.69

Bay Notation



203

Table B.9: 6-Storey Building Facade System, Inter- storey drift (mm) for UN structure and structure with VE damping connections, considering X direction.

UN VE %Reduction UN VE % Reduction UN VE % ReductionS0-1 23.17 6.99 69.83 27.74 6.52 76.48 38.70 10.05 74.03S1-2 10.47 2.84 72.92 12.53 2.57 79.51 16.62 3.98 76.03S2-3 8.05 1.83 77.29 8.76 1.54 82.46 12.33 2.44 80.19S3-4 6.97 1.34 80.83 6.21 1.07 82.80 10.68 1.74 83.70S4-5 4.89 0.84 82.90 3.88 0.65 83.26 7.32 1.08 85.31S5-6 2.35 0.37 84.17 2.04 0.28 86.19 3.38 0.48 85.96

NorthridgeStoreys

El-Centro Kobe

Table B.10: 6-Storey Building Facade System, Deformation in connections (mm) under load case 2, for UN structure and structure with VE damping connections.



Table B.11: 6-Storey Building Facade System, Axial force in connections (kN) under load case 2 for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 66.8 18.8 71.86 107.95 20.6 80.92 110.05 27.8 74.74

S.3 48.07 15.4 67.96 85.77 16.2 81.11 85.12 20.4 76.03

S.4 43.68 15 65.66 77.54 15.6 79.88 77.77 18 76.85

S.5 34.37 15.4 55.19 59.14 15.6 73.62 59.74 16.6 72.21

S.6 21.45 13.2 38.46 32.89 13.2 59.87 32.8 13.4 59.15


Table B.12: 6-Storey Building Facade System, Differential displacement between frame and facade (mm) under load case 2, for UN structure and structure with VE damping connections.




204

Table B.13: 6-Storey Building Facade System, Distortion of facade (mm) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 2.50E-04 6.50E-05 74.00 4.25E-04 7.25E-05 82.94 4.28E-04 1.03E-04 76.02S.3 1.93E-04 5.00E-05 74.03 3.70E-04 5.25E-05 85.81 3.75E-04 7.75E-05 79.33S.4 1.70E-04 4.25E-05 75.00 3.30E-04 4.25E-05 87.12 3.58E-04 6.25E-05 82.52S.5 1.45E-04 3.25E-05 77.59 3.33E-04 3.25E-05 90.23 3.07E-04 4.75E-05 84.55S.6 1.13E-04 2.75E-05 75.56 2.43E-04 4.00E-05 83.51 2.23E-04 3.75E-05 83.15


Table B.14: 6 -Storey Building Facade System, Inter- storey drift (mm) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS0-1 18.12 5.01 72.35 27.99 5.54 80.21 29.06 7.68 73.57S1-2 7.63 2.05 73.13 12.67 2.24 82.32 12.86 3.11 75.82S2-3 5.04 1.31 74.01 9.47 1.41 85.11 9.59 1.98 79.35S3-4 3.83 0.97 74.67 7.71 1.01 86.90 8.3 1.45 82.53S4-5 2.84 0.63 77.82 6.31 0.64 89.86 6.19 0.92 85.14S5-6 1.45 0.32 77.93 3.59 0.31 91.36 3.22 0.45 86.02


Table B.15: 6-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections. Effects of facade mass.

180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm)S.2 3.51 3.34 3.01 5.48 5.39 5.25 5.73 5.5 5.07S.3 2.57 2.4 2.17 4.23 4.27 4.35 4.36 4.25 4.08S.4 2.38 2.18 2.006 3.74 3.87 3.9 3.96 3.88 3.73S.5 1.87 1.71 1.555 2.91 2.95 2.94 3.05 2.98 2.85S.6 1.14 1.07 0.932 1.68 1.64 1.59 1.69 1.64 1.53

Kobe NorthridgeStoreys

El-Centro

Table B.16: 6-Storey Building Facade System, Axial forces in connections (kN) for UN structure and structure with VE damping connections. Effects of facade mass.




205

Table B.17: 6-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections. Effects of facade mass.



Table B.18: 6-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections. Effects of facade mass.

180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm)S.2 2.58E-04 2.50E-04 2.35E-04 4.30E-04 4.25E-04 4.25E-044.43E-04 4.28E-04 3.93E-04S.3 2.05E-04 1.93E-04 1.80E-04 3.83E-04 3.70E-04 4.10E-043.85E-04 3.75E-04 3.62E-04S.4 1.80E-04 1.70E-04 1.58E-04 3.42E-04 3.30E-04 4.03E-043.63E-04 3.58E-04 3.55E-04S.5 1.57E-04 1.45E-04 1.33E-04 2.78E-04 3.33E-04 3.42E-043.10E-04 3.07E-04 2.98E-04S.6 1.23E-04 1.13E-04 9.25E-05 2.03E-04 2.43E-04 2.45E-042.27E-04 2.23E-04 2.15E-04


Storeys

Table B.19: 6 - Storey Building Facade System, Inter- storey drifts (mm), for UN structure and structure with VE damping connections. Effects of facade mass.

180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm) 180 (mm) 150 (mm) 100(mm)S0-1 19.1 18.12 16.39 27.92 27.99 26.54 30.139 29.06 27.15S1-2 7.98 7.63 7.01 12.9 12.67 12.35 13.351 12.86 11.72S2-3 5.28 5.04 4.609 9.88 9.47 10.25 9.94 9.59 9.12S3-4 4.1 3.83 3.531 8.03 7.71 9.26 8.48 8.3 8.11S4-5 3.17 2.84 2.47 5.53 6.31 6.92 6.26 6.19 5.97S5-6 1.67 1.45 1.2 2.82 3.59 3.65 3.27 3.22 3.16


Storeys


206


207

Appendix C


Table C.1: 12-Storey Building Facade System, Deformation in connections (mm,) for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 12.58 2.77 78.0 6.23 2.42 61.2 12.40 4.07 67.2S.3 10.87 2.36 78.3 4.96 2.02 59.3 11.48 3.42 70.2S.4 9.38 2.09 77.7 5.25 1.74 66.9 10.86 2.97 72.7S.5 8.51 1.84 78.4 5.08 1.42 72.0 9.87 2.48 74.9S.6 8.82 1.59 82.0 4.60 1.20 73.9 8.56 2.11 75.4S.7 8.66 1.34 84.5 5.29 1.01 80.9 7.97 1.77 77.8S.8 7.75 1.08 86.1 5.74 0.76 86.8 7.28 1.40 80.8S.9 6.13 0.83 86.5 6.12 0.56 90.8 6.18 1.05 83.0S.10 4.73 0.60 87.3 5.92 0.42 92.9 4.76 0.76 84.0S.11 3.24 0.35 89.2 4.62 0.25 94.6 3.26 0.45 86.2S.12 1.59 0.11 93.1 2.45 0.09 96.3 1.63 0.17 89.6

Storeys


Table C.2: 12-Storey Building Facade System, Axial force in connections (kN) for UN structure and structure with VE damping connections.



Table C.3: 12-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections.




208

Table C.4: 12-Storey Building Facade System, Distortion of facade (radian), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 1.05E-03 2.31E-04 78.1 4.32E-04 1.87E-04 56.7 1.08E-033.26E-04 69.9S.3 1.04E-03 2.24E-04 78.4 3.19E-04 1.70E-04 46.7 1.16E-033.05E-04 73.7S.4 1.01E-03 2.24E-04 77.8 2.33E-04 1.60E-04 31.3 1.22E-032.95E-04 75.8S.5 9.54E-04 2.18E-04 77.1 3.21E-04 1.49E-04 53.6 1.23E-032.82E-04 77.1S.6 8.89E-04 2.18E-04 75.5 6.43E-04 1.40E-04 78.2 1.19E-032.68E-04 77.5S.7 8.23E-04 2.10E-04 74.5 6.56E-04 1.33E-04 79.7 1.13E-032.56E-04 77.3S.8 7.77E-04 1.99E-04 74.4 7.29E-04 1.21E-04 83.4 1.07E-032.44E-04 77.3S.9 1.13E-03 1.83E-04 83.9 8.49E-04 1.13E-04 86.7 1.10E-032.21E-04 79.8S.10 1.07E-03 1.70E-04 84.1 8.71E-04 1.07E-04 87.7 1.07E-03 2.02E-04 81.2S.11 9.73E-04 1.51E-04 84.5 7.88E-04 9.76E-05 87.6 9.79E-04 1.87E-04 80.9S.12 8.44E-04 1.37E-04 83.8 6.69E-04 9.05E-05 86.5 8.63E-04 1.68E-04 80.5


Table C.5: 12-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections, considering X direction.



Table C.6: 12-Storey Building Facade System, Axial force in connections (kN) for UN structure and structure with VE damping connections, considering X direction.




209

Table C.7: 12-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections, considering X direction.



Table C.8: 12-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections, considering X direction.



Table C.9: 12- Storey Building Facade System, Interstorey- drift (mm), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS0-1 29.42 6.66 77.4 15.38 5.98 61.1 28.76 9.92 65.5S1-2 29.71 6.52 78.1 14.10 5.56 60.5 29.27 9.45 67.7S2-3 26.03 5.55 78.7 10.18 4.47 56.1 28.04 7.78 72.3S3-4 22.76 4.98 78.1 7.61 3.72 51.2 26.87 6.69 75.1S4-5 19.28 4.40 77.2 8.30 3.03 63.4 24.83 5.67 77.2S5-6 16.02 3.95 75.4 11.57 2.52 78.2 21.94 4.83 78.0S6-7 13.02 3.45 73.5 10.80 2.08 80.7 18.49 4.06 78.0S7-8 10.69 2.91 72.7 11.36 1.63 85.7 15.71 3.22 79.5S8-9 16.19 2.33 85.6 13.06 1.48 88.7 14.77 2.61 82.3S9-10 13.66 1.77 87.0 12.58 1.24 90.2 12.81 2.02 84.2S10-11 10.04 1.24 87.7 9.41 0.68 92.8 9.27 1.39 85.0S11-12 5.86 0.73 87.5 5.27 0.40 92.5 5.40 0.82 84.8



210

Table C.10: 12-Storey Building Facade System, Deformation of connections (mm) under load case 2, for UN structure and structure with VE damping connections.


Storeys


Table C.11: 12-Storey Building Facade System, Axial force in connections (kN) under load case 2 for UN structure and structure with VE damping connections.


Storeys


Table C.12: 12-Storey Building Facade System, Differential displacement between frame and facade (mm) under load case 2, for UN structure and structure with VE damping connections.




211

Table C.13: 12-Storey Building Facade System, Distortion of facade (radian) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 5.02E-04 1.63E-04 67.66 5.43E-04 1.58E-04 70.97 8.37E-04 2.40E-04 71.34S.3 5.05E-04 1.55E-04 69.31 5.10E-04 1.43E-04 72.06 8.93E-04 2.25E-04 74.79S.4 5.13E-04 1.58E-04 69.27 4.63E-04 1.38E-04 70.27 9.58E-04 2.18E-04 77.28S.5 5.05E-04 1.55E-04 69.31 4.18E-04 1.27E-04 69.46 1.01E-03 2.08E-04 79.46S.6 4.80E-04 1.48E-04 69.27 5.52E-04 1.20E-04 78.28 1.02E-03 1.98E-04 80.54S.7 6.25E-04 1.40E-04 77.60 8.57E-04 1.15E-04 86.59 9.93E-04 1.88E-04 81.11S.8 6.05E-04 1.33E-04 78.10 8.40E-04 1.05E-04 87.50 9.48E-04 1.75E-04 81.53S.9 8.10E-04 1.25E-04 84.57 8.28E-04 9.75E-05 88.22 8.95E-04 1.63E-04 81.84S.10 7.82E-04 1.13E-04 85.62 8.33E-04 9.25E-05 88.89 8.35E-04 1.50E-04 82.04S.11 7.03E-04 1.05E-04 85.05 7.97E-04 8.50E-05 89.34 7.60E-04 1.38E-04 81.91S.12 6.05E-04 9.50E-05 84.30 7.03E-04 8.00E-05 88.61 6.80E-04 1.25E-04 81.62


Table C.14: 12 Storey Building Facade System, Inter- storey drift (mm) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS1-2 14.05 4.63 67.05 16.05 4.90 69.47 22.86 7.18 68.59S2-3 12.50 3.85 69.20 15.78 4.62 70.72 22.98 6.89 70.02S3-4 12.50 3.85 69.20 13.08 3.75 71.33 20.76 5.69 72.59S4-5 11.55 3.48 69.87 10.45 3.15 69.86 20.31 4.90 75.87S-5-6 10.42 3.07 70.54 7.90 2.61 66.96 19.78 4.18 78.87S6-7 8.95 2.66 70.28 10.56 2.18 79.36 18.40 3.55 80.71S7-8 10.05 2.26 77.51 14.75 1.80 87.80 16.43 2.98 81.86S8-9 9.26 1.91 79.37 13.38 1.43 89.31 14.24 2.44 82.87S9-10 11.90 1.55 86.97 12.04 1.12 90.70 11.99 1.93 83.90S10-11 10.55 1.19 88.72 11.11 0.88 92.08 9.63 1.49 84.53S11-12 7.75 0.83 89.29 9.15 0.61 93.33 7.04 1.06 84.94

Storeys


Table C.15: 12-Storey Building Facade System, Deformation of connections (mm) under higher load (0.5g), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 14.98 4.88 67.4 17.03 5.08 70.2 24.39 7.49 69.3S.3 13.17 4.14 68.6 14.31 4.22 70.5 21.72 6.25 71.2S.4 11.99 3.68 69.3 13.23 3.66 72.3 20.86 5.45 73.9S.5 11.78 3.23 72.6 14.62 3.07 79.0 19.79 4.6 76.8S.6 12.35 2.83 77.1 15.12 2.62 82.7 19.01 3.91 79.4S.7 12.71 2.45 80.7 14.41 2.27 84.2 17.28 3.35 80.6S.8 12.48 2.09 83.3 12.81 1.89 85.2 14.42 2.74 81.0S.9 11.59 1.76 84.8 12.43 1.57 87.4 11.15 2.1 81.2S.10 9.86 1.47 85.1 11.61 1.37 88.2 9.69 1.76 81.8S.11 7.15 1.25 82.5 9.15 1.21 86.8 7.06 1.39 80.3S.12 3.89 1.01 74.0 5.22 1 80.8 3.66 1.04 71.6



212

Table C.16: 12-Storey Building Facade System, Axial force in connections (kN) under higher load of (0.5g), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 299.69 97.6 67.4 340.62 101.6 70.2 487.86 149.8 69.3S.3 263.48 82.8 68.6 286.26 84.4 70.5 434.57 125 71.2S.4 239.8 73.6 69.3 264.67 73.2 72.3 417.33 109 73.9S.5 235.75 64.6 72.6 292.405 61.4 79.0 395.9 92 76.8S.6 247.01 56.6 77.1 302.58 52.4 82.7 380.35 78.2 79.4S.7 254.35 49 80.7 288.38 45.4 84.3 345.65 67 80.6S.8 249.71 41.8 83.3 256.38 37.8 85.3 288.47 54.8 81.0S.9 231.84 35.2 84.8 248.73 31.4 87.4 223.14 42 81.2S.10 197.32 29.4 85.1 232.32 27.4 88.2 193.88 35.2 81.8S.11 143.06 25 82.5 183.04 24.2 86.8 141.35 27.8 80.3S.12 77.93 20.2 74.1 104.42 20 80.8 73.29 20.8 71.6


Table C.17: 12-Storey Building Facade System, Differential displacement between frame and facade (mm) under higher load of (0.5g), for UN structure and structure with VE damping connections.



Table C.18: 12- Storey Building Facade System, Distortion of facade (radian) under higher load of (0.5g), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 1.26E-03 4.05E-04 67.8 1.36E-03 3.93E-04 71.1 2.09E-036.00E-04 71.3S.3 1.26E-03 3.90E-04 69.0 1.27E-03 3.60E-04 71.7 2.24E-035.63E-04 74.8S.4 1.28E-03 3.93E-04 69.4 1.15E-03 3.40E-04 70.5 2.39E-035.43E-04 77.3S.5 1.26E-03 3.83E-04 69.7 1.04E-03 3.20E-04 69.3 2.53E-035.17E-04 79.5S.6 1.20E-03 3.70E-04 69.0 1.38E-03 3.00E-04 78.3 2.54E-034.95E-04 80.5S.7 1.56E-03 3.48E-04 77.7 2.14E-03 2.85E-04 86.7 2.47E-034.68E-04 81.1S.8 1.51E-03 3.35E-04 77.9 2.10E-03 2.65E-04 87.4 2.37E-034.35E-04 81.6S.9 2.03E-03 3.10E-04 84.7 2.07E-03 2.45E-04 88.1 2.24E-034.05E-04 81.9S.10 1.96E-03 2.85E-04 85.4 2.08E-03 2.30E-04 89.0 2.09E-03 3.75E-04 82.0S.11 1.76E-03 2.58E-04 85.3 1.99E-03 2.10E-04 89.5 1.90E-03 3.45E-04 81.8S.12 1.51E-03 2.35E-04 84.5 1.75E-03 1.92E-04 89.0 1.70E-03 3.13E-04 81.6



213

Table C.19: 12- Storey Building Facade System, Inter- storey drift (mm), under higher load of (0.5g), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS1-2 35.14 11.59 67.02 40.12 12.25 69.47 57.15 17.96 68.57S2-3 31.24 9.62 69.21 39.46 11.57 70.68 57.47 17.22 70.04S3-4 31.24 9.62 69.21 32.7 9.37 71.35 51.89 14.24 72.56S4-5 28.89 8.71 69.85 26.12 7.87 69.87 50.78 12.26 75.86S5-6 26.04 7.67 70.55 19.75 6.52 66.99 49.45 10.45 78.87S6-7 22.38 6.64 70.33 26.42 5.44 79.41 46 8.87 80.72S7-8 25.13 5.65 77.52 36.86 4.5 87.79 41.09 7.45 81.87S8-9 23.15 4.79 79.31 33.46 3.59 89.27 35.6 6.09 82.89S9-10 29.75 3.87 86.99 30.08 2.81 90.66 29.97 4.83 83.88S10-11 26.38 2.98 88.70 27.79 2.19 92.12 24.08 3.739 84.47S11-12 19.37 2.08 89.26 22.87 1.52 93.35 17.59 2.631 85.04


Table C.20: 12-Storey Building Facade System, Deformation of connections (mm), for UN structure and structure with VE damping connections, considering glass facades.

Earthquake Storeys UN VE % ReductionEl-Centro S.2 2.20 1.04 52.95

S.3 2.13 1.02 52.24S.4 1.88 0.96 49.20S.5 1.60 0.88 44.83S.6 1.45 0.80 44.83S.7 1.46 0.72 50.86S.8 1.33 0.62 53.38S.9 1.14 0.53 53.74S.10 0.97 0.44 54.92S.11 0.75 0.35 53.02S.12 0.50 0.28 44.11

Table C.21: 12-Storey Building Facade System, Axial force in connections (kN), for UN structure and structure with VE damping connections, considering glass facade.


S.3 10.63 5.08 52.26S.4 9.42 4.78 49.28S.5 7.99 4.40 44.90S.6 7.27 4.00 44.94S.7 7.30 3.58 50.99S.8 6.67 3.10 53.49S.9 5.68 2.63 53.74S.10 4.83 2.18 54.92S.11 3.75 1.75 53.27S.12 2.51 1.40 44.11


214

Table C.22: 12- Storey Building Facade System, Differential displacement between frame and facade (mm), for UN structure and structure with VE damping connections, considering glass facade.


S.3 2.23 1.04 53.26S.4 1.98 0.97 51.14S.5 1.62 0.89 45.20S.6 1.26 0.80 36.90S.7 0.99 0.70 28.93S.8 0.70 0.59 15.11S.9 0.46 0.48 3.23S.10 0.33 0.36 9.09S.11 0.23 0.24 6.67S.12 0.17 0.12 29.41

Table C.23: 12- Storey Building Facade System, Differential displacement between upper and lower facades (mm), for UN structure and structure with VE damping connections, considering glass facade.

Earthquake Storeys UN VE % ReductionEl-Centro S.2-3 4.50 2.10 53.28

S.3-4 4.14 2.00 51.81S.4-5 3.50 1.84 47.50S.5-6 2.77 1.67 39.89S.6-7 2.20 1.48 32.73S.7-8 1.60 1.26 21.32S.8-9 1.09 1.03 5.53S.9-10 0.77 0.81 5.19S.10-11 0.55 0.56 1.91S.11-12 0.41 0.32 21.95

Table C.24: 12 Storey Building Facade System, Inter - storey drifts (mm), for UN structure and structure with VE damping connections.

Earthquake Storeys UN VE % ReductionEl-Centro S0-1 7.00 3.41 51.36

S1-2 10.48 4.81 54.13S 2-3 8.89 4.45 49.94S 3-4 8.89 4.45 49.94S 4-5 7.34 4.14 43.66S 5-6 5.95 3.78 36.42S 6-7 4.65 3.35 27.88S 7-8 3.40 2.89 15.15S 8-9 2.51 2.41 3.98S 9-10 1.96 1.88 4.09S 10-11 1.60 1.33 16.88S 11-12 1.20 0.82 32.08


215

Appendix D


Table D.1: 18-Storey Building Facade System, Deformation of connections (mm), for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 14.30 4.69 67.2 8.11 3.11 61.7 10.70 5.73 46.4S.3 13.68 4.41 67.8 7.92 2.86 63.9 9.94 5.16 48.1S.4 12.76 4.22 66.9 8.03 2.71 66.3 9.83 4.84 50.8S.5 11.10 4.00 64.0 7.82 2.57 67.1 9.97 4.50 54.9S.6 9.70 3.70 61.9 7.21 2.35 67.4 10.10 4.04 60.0S.7 10.11 3.39 66.5 6.54 2.12 67.6 9.99 3.64 63.6S.8 10.45 3.11 70.2 5.88 1.94 67.0 9.54 3.37 64.7S.9 10.48 2.85 72.8 5.51 1.81 67.2 8.71 3.11 64.3S.10 10.54 2.57 75.6 6.06 1.66 72.6 8.32 2.85 65.7S.11 10.40 2.26 78.3 6.31 1.44 77.2 8.21 2.51 69.4S.12 10.08 1.93 80.9 6.42 1.21 81.2 7.72 2.17 71.9S.13 9.30 1.63 82.5 6.56 0.98 85.1 6.91 1.83 73.5S.14 8.10 1.33 83.6 6.62 0.85 87.2 6.63 1.51 77.2S.15 7.14 1.03 85.6 6.31 0.69 89.1 5.90 1.18 80.0S.16 5.80 0.70 87.9 5.41 0.46 91.5 4.88 0.81 83.4S.7 3.92 0.38 90.3 3.83 0.23 94.0 3.63 0.43 88.2S.18 2.03 0.12 94.1 1.88 0.10 94.9 1.80 0.12 93.2


Table D.2: 18-Storey Building Facade System, Axial force in connections (kN), for UN structure and structure with VE damping connections.




216

Table D.3: 18-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections.


Storeys El-Centro Kobe Northridge

Table D.4: 18-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 1.23E-03 4.44E-04 63.8 7.02E-04 2.89E-04 58.8 1.01E-034.97E-04 50.6S.3 1.31E-03 5.00E-04 61.9 7.61E-04 3.18E-04 58.2 1.08E-035.16E-04 52.0S.4 1.35E-03 5.45E-04 59.7 8.13E-04 3.44E-04 57.7 1.26E-035.43E-04 57.0S.5 1.29E-03 5.73E-04 55.5 8.29E-04 3.65E-04 56.0 1.35E-035.65E-04 58.0S.6 1.23E-03 6.02E-04 50.9 7.92E-04 3.81E-04 51.9 1.74E-035.74E-04 66.9S.7 1.18E-03 6.15E-04 48.0 7.37E-04 3.91E-04 46.9 1.84E-035.78E-04 68.6S.8 1.18E-03 6.23E-04 47.3 6.72E-04 3.96E-04 41.1 1.90E-035.85E-04 69.2S.9 1.23E-03 6.27E-04 49.1 5.99E-04 4.00E-04 33.2 1.92E-035.87E-04 69.4S.10 1.46E-03 6.27E-04 57.1 5.21E-04 3.99E-04 23.4 1.87E-03 6.97E-04 62.7S.11 1.63E-03 6.12E-04 62.3 4.29E-04 3.93E-04 8.4 1.94E-036.88E-04 64.4S.12 1.99E-03 5.97E-04 70.1 3.29E-04 3.86E-04 17.3 2.01E-03 6.72E-04 66.6S.13 2.10E-03 5.77E-04 72.6 2.44E-04 3.73E-04 52.9 2.02E-03 6.56E-04 67.5S.14 2.15E-03 5.56E-04 74.1 1.77E-04 3.62E-04 104.5 1.98E-03 6.35E-04 67.8S.15 2.25E-03 5.46E-04 75.8 1.31E-04 3.50E-04 167.2 1.90E-03 6.11E-04 67.8S.16 2.24E-03 5.19E-04 76.9 1.49E-03 3.33E-04 77.6 1.81E-03 5.84E-04 67.8S.7 2.15E-03 4.96E-04 76.9 1.43E-03 3.19E-04 77.7 1.68E-035.59E-04 66.7S.18 2.00E-03 4.75E-04 76.3 1.32E-03 3.04E-04 77.0 1.63E-03 5.31E-04 67.4

Storeys El-Centro Kobe Northridge


217

Table D.5: 18-Storey Building Facade System, Deformation in connections (mm) for UN structure and structure with VE damping connections, considering X direction.



Table D.6: 18-Storey Building Facade System, Axial forces in connections (kN) for UN structure and structure with VE damping connections, considering X direction.



Table D.7: 18-Storey Building Facade System, Differential displacement between frame and facade (mm) for UN structure and structure with VE damping connections, considering X direction.



Table D.8: 18-Storey Building Facade System, Distortion of facade (radian) for UN structure and structure with VE damping connections, considering X direction.




218

Table D.9: 18-Storey Building Facade System, Inter-storey drifts (mm) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.0-1 27.91 9.33 66.6 15.94 6.26 60.8 13.24 7.04 46.8S.1-2 34.13 11.34 66.8 19.33 7.46 61.4 25.53 13.52 47.0S.2-3 33.05 11.01 66.7 18.93 7.03 62.9 23.20 12.27 47.1S.3-4 30.99 10.68 65.5 18.68 6.71 64.1 23.89 11.35 52.5S.4-5 26.77 10.23 61.8 17.69 6.42 63.7 24.25 10.52 56.6S.5-6 22.22 9.81 55.9 15.74 6.09 61.3 25.70 9.58 62.7S.6-7 18.17 9.21 49.3 13.35 5.76 56.9 26.76 8.69 67.5S.7-8 15.63 8.60 45.0 11.04 5.43 50.8 26.09 7.99 69.4S.8-9 15.36 8.04 47.6 8.92 5.12 42.6 24.53 7.66 68.8S.9-10 16.08 7.45 53.7 6.67 4.76 28.6 22.63 8.40 62.9S.10-11 17.68 6.75 61.8 4.21 4.33 3.1 21.75 7.71 64.5S.11-12 21.74 6.02 72.3 1.73 3.91 125.7 22.25 6.98 68.6S.12-13 22.55 5.34 76.3 0.40 3.49 768.0 21.36 6.22 70.9S.13-14 21.99 4.67 78.8 1.96 3.07 57.0 19.14 5.48 71.4S.14-15 20.70 4.07 80.3 1.46 2.64 80.6 16.40 4.68 71.5S.15-16 18.75 3.32 82.3 14.58 2.15 85.2 13.39 3.83 71.4S.16-17 15.38 2.56 83.3 11.68 1.66 85.8 10.24 2.97 70.9S.17-18 10.53 1.94 81.6 7.70 1.24 83.9 7.31 2.21 69.7


Table D.10: 18-Storey Building Facade System, Deformation of connections (mm) under load case 2, for UN structure and structure with VE damping connections.


Kobe Northridge

Storeys

El-Centro


219

Table D.11: 18-Storey Building Facade System, Axial force in connections (kN) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 261.49 70.8 72.92 152.23 51.8 65.97 232.92 93.2 59.99S.3 251.07 65.6 73.87 135.08 46.8 65.35 220.68 84.6 61.66S.4 240.37 62.2 74.12 119.36 44.2 62.97 214.49 79.4 62.98S.5 218.99 59 73.06 107.37 42 60.88 209.25 74.6 64.35S.6 192.49 55.6 71.12 102.41 38.6 62.31 203.22 68 66.54S.7 181.61 52 71.37 98.63 36 63.50 198.65 61.2 69.19S.8 195.14 48.6 75.09 97.16 34.4 64.59 189.59 55.8 70.57S.9 202.69 45.4 77.60 102.16 33.2 67.50 176.31 52 70.51S.10 202.85 42.4 79.10 101.44 32 68.45 159.81 48.4 69.71S.11 197.27 39.2 80.13 96.15 30.4 68.38 142.64 44.6 68.73S.12 186.8 35.8 80.84 115.04 29 74.79 129.15 40.8 68.41S.13 167.88 33 80.34 130.96 28 78.62 114.98 37.2 67.65S.14 141.56 30.8 78.24 136.89 27 80.28 107.49 33.8 68.56S.15 114.19 28.8 74.78 132.18 26.4 80.03 94.93 30.6 67.77S.16 90.23 27 70.08 115.89 25.8 77.74 79.29 28 64.69S.17 61.53 26 57.74 87.7 25.6 70.81 61.09 26.4 56.79S.18 37.74 23.2 38.53 52.07 23.2 55.44 37.52 23.4 37.63

Storeys Kobe NorthridgeEl-Centro

Table D.12: 18-Storey Building Facade System, Differential displacement between frame and facade (mm) under load case 2, for UN structure and structure with VE damping connections.


Storeys



220

Table D.13: 18-Storey Building Facade System, Distortion of facade (radian) under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS.2 1.17E-03 3.25E-04 72.22 5.80E-04 2.10E-04 63.79 1.15E-03 4.05E-04 64.71S.3 1.33E-03 3.55E-04 73.21 5.43E-04 2.13E-04 60.83 1.31E-03 4.27E-04 67.43S.4 1.44E-03 3.82E-04 73.39 4.90E-04 2.20E-04 55.10 1.46E-03 4.50E-04 69.07S.5 1.47E-03 4.05E-04 72.35 4.30E-04 2.83E-04 34.30 1.57E-03 4.73E-04 69.86S.6 1.45E-03 4.43E-04 69.54 3.85E-04 2.93E-04 24.03 1.64E-03 4.85E-04 70.38S.7 1.45E-03 4.50E-04 68.97 3.80E-04 3.02E-04 20.39 1.69E-03 4.87E-04 71.20S.8 1.46E-03 4.55E-04 68.73 4.25E-04 3.07E-04 27.65 1.72E-03 4.90E-04 71.47S.9 1.50E-03 4.63E-04 69.22 4.70E-04 3.08E-04 34.57 1.89E-03 4.95E-04 73.84S.10 1.54E-03 4.58E-04 70.39 5.22E-04 3.08E-04 41.15 1.92E-03 4.90E-04 74.45S.11 1.82E-03 4.48E-04 75.34 8.30E-04 3.03E-04 63.55 1.91E-03 4.80E-04 74.84S.12 2.09E-03 4.38E-04 79.04 1.28E-03 2.95E-04 76.86 1.88E-03 4.68E-04 75.17S.13 2.19E-03 4.25E-04 80.57 1.36E-03 2.88E-04 78.86 1.84E-03 4.58E-04 75.17S.14 2.21E-03 4.10E-04 81.41 1.41E-03 2.80E-04 80.07 1.79E-03 5.00E-04 71.99S.15 2.14E-03 3.95E-04 81.56 1.40E-03 2.68E-04 80.93 1.72E-03 4.80E-04 72.09S.16 2.05E-03 3.83E-04 81.36 1.36E-03 2.58E-04 81.10 1.65E-03 4.60E-04 72.08S.17 1.94E-03 3.65E-04 81.19 1.29E-03 2.45E-04 80.93 1.57E-03 4.40E-04 71.93S.18 1.82E-03 3.50E-04 80.80 1.19E-03 2.38E-04 79.96 1.50E-03 4.20E-04 71.91

Storeys

Kobe NorthridgeEl-Centro

Table D.14: 18-Storey Building Facade System, Inter-storey drift under load case 2, for UN structure and structure with VE damping connections.

UN VE % Reduction UN VE % Reduction UN VE % ReductionS1-2 25.84 7.04 72.76 15.09 5.18 65.67 23.11 9.3 59.76S2-3 31.18 8.44 72.93 17.47 5.97 65.83 28.27 10.94 61.30S.3-4 30.45 7.96 73.86 15.35 5.35 65.15 27.63 10.06 63.59S.4-5 30.08 7.59 74.77 13.06 4.9 62.48 27.01 9.36 65.35S.5-6 27.47 7.31 73.39 10.74 4.85 54.84 26.42 8.72 66.99S.6-7 24.46 7.17 70.69 8.8 4.68 46.82 26.8 8.03 70.04S.7-8 21.84 6.76 69.05 7.82 4.43 43.35 25.6 7.35 71.29S.8-9 19.74 6.32 67.98 7.72 4.19 45.73 24.03 6.75 71.91S.9-10 18.17 5.89 67.58 7.35 3.92 46.67 23.84 6.25 73.78S.10-11 17.23 5.46 68.31 6.98 3.65 47.71 23.32 5.72 75.47S.11-12 19.27 4.96 74.26 10.56 3.35 68.28 21.74 5.13 76.40S.12-13 21.92 4.47 79.61 15.04 3.03 79.85 20.02 4.53 77.37S.13-14 22.63 3.96 82.50 15.61 2.72 82.58 18.15 4.32 76.20S.14-15 21.71 3.64 83.23 15.57 2.39 84.65 16.09 4.33 73.09S.15-16 19.47 2.77 85.77 14.65 2.04 86.08 13.85 3.71 73.21S.16-17 16.37 2.46 84.97 12.69 1.69 86.68 11.45 3.06 73.28S.17-18 12.64 1.95 84.57 9.81 1.33 86.44 8.97 2.42 73.02

Kobe NorthridgeEl-CentroStoreys

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