Performance Behavior of Confined Brick Masonry …prr.hec.gov.pk/jspui/bitstream/123456789/550/1/358S.pdfHorizontal bed joint reinforcement is recommended to connect the tie columns

Performance Behavior of Confined Brick Masonry Buildings under Seismic Demand

By

AMJAD NASEER

DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of

Philosophy in Civil Engineering

Department of Civil Engineering,

N-W.F.P University of Engineering and Technology,

Peshawar, Pakistan, 2009

© Amjad Naseer 2009. All rights reserved

ii

ABSTRACT

Seismic behavior of typical confined brick masonry buildings has been studied. Single

and double story reduced scale confined brick masonry building models, representing

typical single and double story residential houses in northern Pakistan, have been tested

on simple earthquake simulator. The models have been built at 1:4 reduced scale,

following the laws of complete model similitude and tested by subjecting them to a

sequence of excitations. The models were confined according to the requirements of

Eurocode 8.

The research work was divided into three distinct phases: testing of prototype masonry

materials and assemblages; simulation of reduced scale masonry materials and

assemblage; and shaking table test of reduced scale models. Prototype masonry materials

and assemblage were tested in compression, diagonal compression and cyclic test.

Typical shear failure was observed to be predominant failure mode in both single and

double story models. Although, the walls of single story severely damaged, the confining

element was able to prevent them from disintegration. Damage was concentrated at the

ground floor in the case of double story model. In-plane walls of ground floor were

severely damaged during strong shaking. Horizontal bed joint reinforcement is

recommended to connect the tie columns and ground floor masonry walls that will

improve the seismic behavior of the ground floor walls. Response modification factor of

3.0 and 2.41 was determined for single and double story models respectively, what is in

good correlation with Eurcode spectral amplification factors. The model test results

indicate that prototype single and double story buildings of the tested type will resist, with

moderate damage an earthquake with peak ground acceleration of 0.4 g and 0.25 g,

respectively. The same buildings would resist collapse when subjected to earthquakes up

to 1.0 g.

iii

ACKNOWLEDGMENT

This research work covers the first shaking table test conducted on reduced scale model

building at Earthquake Engineering Center (EEC), N-W.F.P University of Engineering

and Technology (UET), Peshawar. The test being first of its kind in Pakistan on

simulation of confined masonry buildings, many challenges were faced during the entire

research work, i.e., from the simulation of masonry materials to the data processing of the

shaking table test. This work would not have been possible without the support of many

people, especially Prof. Dr. Akhtar Naeem Khan.

I express deep gratitude to my research supervisor Prof. Dr. Akhtar Naeem Khan, who

continuously inspired and supported me during the entire research work. In spite of his

professional engagements, he remained thoroughly involved and provided valuable

suggestions and guidelines during the whole course of study.

I am also highly indebted to Prof. Dr. Miha Tomazevic, ZAG, Ljubljana, Salvenia and

Prof. Dr. Guido Magenese, Pavia University, Italy for their guidance and discussion at

different stages of the research work. I am also thankful to Prof. Miha Tomazevic and

Prof. Sergio M. Alcocer, UNAM, Mexico for sending me research papers as requested by

me during the course of the research work.

I am thankful to fellow Ph.D students Engr. Zakir Hussain, Engr Mohammad Ashraf and

Engr. Khan Shahzad for their help during the construction and testing of the reduced scale

models.

I wish to offer my thanks to the laboratory staff of Concrete, Material Testing, Structural

and EEC laboratories for working day and night with me during the fabrication and

testing of the masonry materials, assemblages and reduced scale model buildings.

Finally, this research could not have materialized without financial support of Higher

Education Commission (HEC) of Pakistan.

iv

NOMENCLATURE

Aw Area of horizontal cross section of wall.

A Net area

ai Acceleration of the ith mass

du Ultimate displacement

de Elastic displacement

E Modulus of elasticity

ft Tensile Strength,

fk Characteristics compressive strength of masonry

fb Normalized compressive strength of masonry unit

fm Compressive strength of mortar

fa & fb Frequencies on either side of the resonant frequency

fn Resonant frequency

G Modulus of Rigidity

g Gauge length

h Height of pier

H Height of specimen in diagonal compression test

∆H Horizontal extension

He Elastic Load

Hu Ultimate design load

Ke Effective Stiffness

l Thickness of the wall

L Length of pier

Mw Earthquake magnitude

mi Mass at the ith story level

v

P Applied load

Psi Pound per square inch

Pcf Pound per cubic feet

Qp Physical Quantity of prototype

Qm Physical Quantity of model

SF Scale Factor

Ss Shear Strength

t thickness of specimen in diagonal compression test

∆V Vertical shortening

W Width of specimen

γ Shear strain

µ Global Ductility Factor

α Coefficient determining the position of the inflection point along

the Height of pier

σ° Compressive stresses in the pier,

τ Tensile stresses in the pier.

σ Standard deviation

Ø Story rotation

ØRmax Story rotation at maximum resistance

Øcr Story rotation at crack limit

Øcoll Story rotation at limit of collapse

vi

ABBREVIATIONS

ASTM American Society for Testing and Material

ATC Applied Technology Council

ACI American Concrete Institute

CLS Cement-Lime-Sand

CLP Cement-Lime-Marble Powder

CLSP Cement-Lime-Sand-Marble Powder

CLSr Cement-Lime-Surkhi

CLSSr Cement-Lime-Sand-Surkhi

COV Coefficient of Variance

CS Cement Sand

CSK Cement-Sand-Khaka

EC Eurocode

EEC Earthquake Engineering Center

EERI Earthquake Engineering and Research Institute

EEFIT Earthquake Engineering Field Investigation Team

FEMA Federal Earthquake Management Agency

GI Galvanized Iron

GMT Greenwich Mean Time

IAEE International Association of Earthquake Engineers

LVDT Linear Variable Displacement Transformer

LSSr Lime-Sand-Surkhi

LSP Lime-Sand-Marble Powder

LS Lime Sand

NEHRP National Earthquake Hazards Reduction Program

NTC-M Mexico City Building Code

N-W.F.P UET N-W.F.P University of Engineering and Technology

PGA Peak Ground Acceleration

PUCP Catholic University of Peru

RC Reinforced Concrete

UBC Uniform Building Code

UNESCO United Nation Education Scientific and Cultural Organization

vii

URM Un-reinforced Masonry

UTM Universal Testing Machine

viii

TABLE OF CONTENT

ABSTRACT ............................................................................................................................ II

ACKNOWLEDGMENT ...................................................................................................... III

NOMENCLATURE .............................................................................................................. IV

ABBREVIATIONS ............................................................................................................... VI

TABLE OF CONTENT ..................................................................................................... VIII

LIST OF FIGURES .............................................................................................................XII

LIST OF TABLES ............................................................................................................. XVI

CHAPTER 1 INTRODUCTION ............................................................................................1

1.1 INTRODUCTION ............................................................................................................1

1.2 AIM AND OBJECTIVES OF THE RESEARCH WORK ..............................................2

1.3 SCOPE OF WORK ..........................................................................................................3

1.4 RESEARCH METHODOLGY ........................................................................................3

1.5 REPORT ORGANIZATION ...........................................................................................4

CHAPTER 2 LITERATURE REVIEW ................................................................................6

2.1 INTRODUCTION ............................................................................................................6

2.2 PROPERTIES OF PAKISTANI MASONRY ..................................................................7

2.2.1 Masonry Unit .............................................................................................................7

2.2.2 Mortar ......................................................................................................................10

2.2.3 Steel bar ...................................................................................................................11

2.3 FAILURE MECHANISM ..............................................................................................13

2.3.1 Un-reinforced Masonry ...........................................................................................13

2.3.2 Confined Masonry ...................................................................................................16

2.4 RESPONSE OF CONFINED MASONRY DURING EARTHQUAKES .....................20

2.4.1 Bam Earthquake (26 December 2003) ....................................................................20

2.4.2 Peru Earthquake (August 15, 2007) ........................................................................21

2.4.3 Central Java Earthquake (May 17, 2006) and Sumatra Earthquake

(December 26, 2004) ...............................................................................................23

2.4.4 Earthquakes in American continent (up to 2000) ....................................................23

2.5 CODES /GUIDELINES RECOMMENDATIONS ........................................................26

2.5.1 Specifications of Eurocode 6 & 8 ............................................................................26

2.5.2 Additional Recommendations .................................................................................28

ix

2.5.3 Confined Masonry Guidelines .................................................................................30

2.6 THEORY OF STRUCTURAL MODEL ........................................................................31

2.7 EXPERIMENTAL TESTING ........................................................................................33

2.7.1 Shaking Table Test on 24 Simple Masonry Building (D.Benedetti,

1998) ........................................................................................................................34

2.7.2 Verification of Seismic Resistance of Confined Masonry Buildings

(Tomzevic, M., 1997) ..............................................................................................34

2.7.3 Shaking Table Tests of Small-Scale Model of Masonry Building:

Advantages and Disadvantages (Tomzevic, M., 2000) ...........................................35

2.7.4 Seismic Behavior of a Three-Story Half Scale Confined Masonry

Structure (Bartolome, A.S., et al., 1992) .................................................................36

2.7.5 Seismic Response Pattern for URM Buildings (Abram 2000) ................................37

2.7.6 Experimental Study on Earthquake Resistant Design of Confined

Masonry Structures (Ishibashi, K., et al., 1992) ......................................................37

2.7.7 Cyclic Loading Tests of Confined Masonry Wall Elements for

Structural Design Development of Apartment Houses in the Third

World (Hiroto Kato et al 1992) ...............................................................................39

CHAPTER 3 EXPERIMENTAL PROGRAM: MASONRY

MATERIALS AND MASONRY ASSEMBLAGE .............................................................40

3.1 INTRODUCTION ..........................................................................................................40

3.2 PROTOTYPE MASONRY TEST .................................................................................41

3.2.1 Masonry Unit (Solid Burnt Clay Brick) ..................................................................41

3.2.2 Masonry Mortar .......................................................................................................43

3.2.3 Prototype Masonry Assemblage ..............................................................................44

3.3 MODEL MASONRY .....................................................................................................57

3.3.1 Model Masonry Unit ...............................................................................................57

3.3.2 Model Masonry Mortar ...........................................................................................59

3.3.3 Micro Concrete ........................................................................................................62

3.3.4 Reinforcing Bar .......................................................................................................63

3.3.5 Model Masonry .......................................................................................................63

3.4 COMPARISON OF MECHANICAL PROPERTIES OF PROTOTYPE

AND MODEL MASONRY ASSEMBLAGE .............................................................76

3.4.1 Masonry Materials ...................................................................................................77

x

3.4.2 Masonry Assemblage ..............................................................................................78

CHAPTER 4 EXPERIMENTAL PROGRAM: SHAKE TABLE TEST .........................79

4.1 INTRODUCTION ..........................................................................................................79

4.2 TYPICAL PAKISTANI MASONRY BUILDING ........................................................79

4.3 FABRICATION OF TYPICAL PAKISTANI MASONRY BUILDING ......................86

4.3.1 Foundation Pad ........................................................................................................86

4.3.2 Masonry Walls ........................................................................................................88

4.3.3 Confining Element ..................................................................................................89

4.3.4 Floor Slab ................................................................................................................92

4.4 PULL OUT TEST ..........................................................................................................94

4.5 DESIGN OF SLAB AND FLOOR BEAM REINFORCEMENT .................................97

4.6 ADDITIONAL FLOOR MASSES ..............................................................................101

4.7 EARTHQUAKE SIMULATOR ..................................................................................106

4.8 INSTRUMENTATIONS AND DATA ACQUISITIONS ...........................................107

4.8.1 Accelerometers ......................................................................................................107

4.8.2 Displacement Transducer and Reference Frame ...................................................110

4.9 GROUND MOTION TIME HISTORY .......................................................................111

4.10 TESTING PROCEDURE ..........................................................................................113

CHAPTER 5 SHAKE TABLE TEST RESULTS .............................................................115

5.1 INTRODUCTION ........................................................................................................115

5.2 SINGLE STORY MODEL BUILDING ......................................................................115

5.2.1 Condition of Model before Test ............................................................................116

5.2.2 Out of plane Walls .................................................................................................117

5.2.3 In-plane Walls .......................................................................................................119

5.2.4 Characteristics Parameters of Shaking Table Motions ..........................................121

5.2.5 Frequency and Damping ratio ...............................................................................122

5.2.6 Acceleration Amplification ...................................................................................124

5.2.7 Torsion Effect ........................................................................................................126

5.2.8 Base Shear .............................................................................................................127

5.2.9 Response Modification Factor of Single Story Model ..........................................130

5.3 DOUBLE STORY MODEL BUILDING ....................................................................132

5.3.1 Condition of Model before Test ............................................................................132

5.3.2 Out of Plane Walls ................................................................................................134

xi

5.3.3 In-plane Walls .......................................................................................................135

5.3.4 Characteristics Parameters of Shaking Table Motions ..........................................138

5.3.5 Torsion Effects ......................................................................................................139

5.3.6 Mode Shape ...........................................................................................................140

5.3.7 Acceleration Amplification ...................................................................................141

5.3.8 Base Shear and First Story Rotation Angle ...........................................................142

5.3.9 Response Modification Factor of Double Story Model ........................................147

5.4 SEISMIC RESISTANCE OF PROTOTYPE BUILDING ..........................................147

5.5 COMPARING SINGLE AND DOUBLE STORY BUILDING .................................149

CHAPTER 6 CONCLUSION AND RECOMMENDATION..........................................151

6.1 SUMMARY .................................................................................................................151

6.2 CONCLUSIONS AND RECOMMENDATIONS.......................................................155

6.3 FUTURE RESEARCH WORK ...................................................................................157

REFERENCES .....................................................................................................................159

APPENDIX A: LIST OF EQUIPMENT ...........................................................................165

APPENDIX B: DESCRIPTION OF EARTHQUAKE SIMULATOR ...........................167

APPENDIX C: MEASURED RESPONSE HISTORIES .................................................169

APPENDIX-D: SCHEMATIC DIAGRAMS SHOWING DAMAGE

PROPAGATION DURING DIFFERENT TEST RUN. ..................................................197

APPENDIX E: ELASTIC ANALYSIS OF SINGLE AND DOUBLE

STORY MODEL BY SAP ..................................................................................................211

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LIST OF FIGURES

Figure 2.1 Adobe brick manufacturing and stacking for sun drying 8

Figure 2.2 Sliding failure 14

Figure 2.3 Shear failure 14

Figure 2.4 Rocking failure and crushing of brick 15

Figure 2.5 Confined masonry walls 17

Figure 2.6 Internal forces direction in confined masonry building to lateral load 18

Figure 2.7 Flexure cracks in confined masonry 19

Figure 2.8 Separation of confining element and masonry wall (Yoshimura et al., 2004) 20

Figure 2.9 Damage to confined masonry building at opening (right side). 21

Figure 2.10 Undamaged six stories confined masonry building in Ice during 15 August, 2007

Peru earthquake (Sventlana Brzev 2007) 22

Figure 2.11 Undamaged two storeys RC confined masonry building next to a collapsed

adobe house in Ica (EEFIT 2008) 22

Figure 2.12 Collapsed confined masonry due to soft stories (EERI 2007). 23

Figure 2.13 Damage confined masonry building (1999 Tehuacan earthquake) due to non-

confinement in window (EERI, 1999) 24

Figure 2.14 Damaged confined masonry during 1985 Llolleo, Chile earthquake (Moroni et

al., 2003) 25

Figure 2.15 Stress-strain relationship of model and prototype materials in the case of

complete model similarity 32

Figure 2.16 Cyclic load test specimens and reinforcement details 38

Figure 3.1 Compressive strength test of solid brick masonry unit 42

Figure 3.2 Compression test of prototype masonry 46

Figure 3.3 Dimensions and instrumentations of prototype specimen for compression test. 46

Figure 3.4 Typical stress strain curve of prototype brick masonry in compression 48

Figure 3.5 Diagonal compression (shear) test 49

Figure 3.6 Dimensions and instrumentations of diagonal tension test 49

Figure 3.7 Dimensions and instrumentations of prototype cyclic load test 52

Figure 3.8 Cyclic test setup 52

xiii

Figure 3.9 Displacement history for prototype cyclic test. 53

Figure 3.10 Typical load-displacement hysteresis loop 54

Figure 3.11 Hysteresis envelop and bilinear idealized curve 54

Figure 3.12 Composition of Surkhi 58

Figure 3.13 Mould for model masonry unit (size 56 x 27 x 17 mm) 59

Figure 3.14 Three different types of model masonry 59

Figure 3.15 Composition of Sand 60

Figure 3.16 Dimensions and instrumentations of model walls for compression. 64

Figure 3.17 Typical stress-strain curve for model brick No.1 66



Figure 3.20 Model wall for tensile (shear) strength 68

Figure 3.21 Model wall during diagonal compression (shear) test 68

Figure 3.22 Dimensions of Model walls 69




Figure 3.26 Model wall test setup 73

Figure 3.27 Displacement-time history for model wall cyclic test 73

Figure 3.28 Load-displacement curve 74

Figure 3.29 Cracked model wall during cyclic test 75

Figure 3.30 Typical hysteresis envelope of model wall for south side loading 76

Figure 4.1 Typical single story prototype building 81

Figure 4.2 Ground floor of typical double story prototype building 82

Figure 4.3 First floor of typical double story prototype building 83

Figure 4.4 Single story confined masonry model building 84

Figure 4.5 Ground floor double story masonry model building 85

Figure 4.6 First floor double story masonry model building 86

Figure 4.7 Through holes in reinforced concrete foundation pad 87

Figure 4.8 Model rebars embedded in foundation concrete 87

Figure 4.9 Under-construction ground story wall 88

xiv

Figure 4.10 Toothing at the end and walls junction 89

Figure 4.11 Fabrication of stirrup for bond beam and tie column 90

Figure 4.12 Model bond and floor beam reinforcement 90

Figure 4.13 Rebars fixing for floor beam 91

Figure 4.14 Micro concrete pouring in tie column 91

Figure 4.15 Tie column after removal of form work 92

Figure 4.16 Concrete pouring in floor beam in double story model 92

Figure 4.17 Slab reinforcement prior to concrete pouring 93

Figure 4.18 Concrete pouring for single story floor slab 93

Figure 4.19 Pullout test specimens 94

Figure 4.20 Pullout Test Set up 95

Figure 4.21 Details of pullout Test Specimens 95

Figure 4.22 Slab reinforcement details of single story building 98

Figure 4.23 Slab reinforcement details of ground floor double story building 99

Figure 4.24 Slab reinforcement details of first floor double story building 100

Figure 4.25 Reinforcement details of floor beams and confining elements 101

Figure 4.26 Additional masses on single story model 103

Figure 4.27 Additional masses on ground floor of double story model 104

Figure 4.28 Additional masses on first floor of double story model 105

Figure 4.29 Additional masses on single story model 106

Figure 4.30 Additional masses on double story model 106

Figure 4.31 Single degree of freedom earthquake simulator (shake table) 107

Figure 4.32 Instrumentation details of single story model 108

Figure 4.33 Instrumentation details of double story model (elevation) 109

Figure 4.34 Instrumentation details of double story model (plan) 110

Figure 4.35 Reference frame for displacement transducer. 111

Figure 4.36 Prototype acceleration time history 112

Figure 4.37 Model acceleration time history 113

Figure 4.38 Lifting operation of double story building 114

Figure 5.1 Grid lines-single story model 116

Figure 5.2 Hairline cracks in roof slab and out-of-plane walls before test 117

xv

Figure 5.3 Sliding of roof slab and cracks in out of plane wall 1 after final test run 118

Figure 5.4 Cracks in out of plane wall 12 after final test run 118

Figure 5.5 Damage to in-plane wall (grid A) at the end of test 119

Figure 5.6 Damage to in-plane wall at grid C and F at the end of test 119

Figure 5.7 Fourier amplitude spectra before the start of test 123

Figure 5.8 Fourier amplitude spectra after test run R175 124

Figure 5.9 Acceleration amplification of single story model 125

Figure 5.10 Base shear coefficient and story rotation plot for single story model 129

Figure 5.11 Hysteretic envelope and idealized bilinear relation 131

Figure 5.12 Grid lines- double story model 133

Figure 5.13 Cracks in wall 1 135

Figure 5.14 Cracks in wall 9 135

Figure 5.15 Damage to ground floor wall A 136

Figure 5.16 Damage to ground floor wall F 136

Figure 5.17 Mode shapes corresponding to each test run 141

Figure 5.18 Story resistance envelop 144

Figure 5.19 Story resistance envelop 146

Figure 5.20 Hysteretic envelope and idealised bilinear relation 147

xvi

LIST OF TABLES

Table 2.1 Physical and mechanical properties of burnt clay brick ........................................... 8

Table 2.2 Absorption of burnt clay brick .................................................................................. 8

Table 2.3 Dimensions and compressive strength of concrete block ....................................... 10

Table 2.4 Compressive strength of mortar collected from field ............................................. 11

Table 2.5 Characteristics of #3 (3/8 inch diameter) bar .......................................................... 12

Table 2.6 Characteristics of #4 (1/2 inch diameter) bar .......................................................... 12

Table 2.7 Recommended allowable number of stories above ground and minimum area of

shear walls for simple buildings (EC 8) .................................................................................. 28

Table 2.8 Typical reinforcement of vertical confining element ............................................ 29

Table 2.9 Recommended maximum building height and number of stories (n) .................... 30

Table 2.10 Similitude requirements in dynamic testing ......................................................... 33

Table 3.1 Compressive strength of masonry unit (solid burnt clay brick) .............................. 42

Table 3.2 Water absorption of burnt clay brick ...................................................................... 43

Table 3.3 Compressive strength of masonry mortar .............................................................. 44

Table 3.4 Compressive strength and modulus of elasticity of prototype brick masonry ....... 47

Table 3.5 Tensile strength and modulus of rigidity of prototype brick masonry .................. 50

Table 3.6 Dimensions and mechanical properties of prototype masonry .............................. 55

Table 3.7 Target mechanical values of materials ................................................................... 57

Table 3.8 Compressive strength and density of model masonry units .................................. 59

Table 3.9 Compressive strength of cement based-masonry mortar ....................................... 61

Table 3.10 Compressive strength of lime based-masonry mortar ......................................... 62

Table 3.11 Compressive strength of micro-concrete ............................................................. 63

Table 3.12 Compressive strength and modulus of elasticity of model masonry ................... 65

Table 3.13 Tensile (shear) strength and modulus of rigidity of model masonry ................... 70

Table 3.14 Mechanical properties of model walls .................................................................. 75

Table 3.15 Actual and true scale factor for masonry materials ............................................. 78

Table 3.16 Actual and true scale factor for masonry assemblage .......................................... 78

Table 4.1 Wall-density ratios of buildings ............................................................................. 80

xvii

Table 4.2 Wall-density ratios of selected buildings ............................................................... 81

Table 4.3 Pull out test results ................................................................................................. 96

Table 4.4 Correlation of prototype to model ....................................................................... 102

Table 5.1 Characteristic parameters of shake table motion .................................................. 122

Table 5.2 Frequency and coefficient of viscous damping .................................................... 123

Table 5.3 Floor acceleration amplification ........................................................................... 125

Table 5.4 Top slab displacements during different test run .................................................. 127

Table 5.5 Base shear coefficient and rotation angle of single story model .......................... 129

Table 5.6 Base shear coefficient and story rotation at limit state levels ............................... 130

Table 5.7 Characteristic parameters of shake table motion .................................................. 139

Table 5.8 Slab displacements during different test run ......................................................... 140

Table 5.9 Acceleration amplification .................................................................................... 142

Table 5.10 Base shear coefficient and story rotation angle .................................................. 143

Table 5.11 Base shear and first story ratio at maximum and ultimate state ......................... 145

Table 5.12 Base shear and first story ratio at maximum and ultimate state ......................... 146

Table 5.13 Modeling scale factors to extrapolate model test results to prototype building . 148

Table 5.14 Parameters of seismic resistance for single story building ................................. 149

Table 5.15 Parameters of seismic resistance for double story building ................................ 149

Table 6.1 Parameters of Seismic Resistance for Single Story building ................................ 155

Table 6.2 Parameters of Seismic Resistance for Double Story building .............................. 155

1

CHAPTER 1 INTRODUCTION

1.1 INTRODUCTION

Masonry is one of the oldest construction materials providing shelter against environmental

and natural hazard. Masonry has been used in different forms in different regions of the

world, as stone masonry buildings; timber reinforced stone buildings, un-reinforced brick and

concrete block and recently as reinforced and confined brick and/or block masonry. Masonry

is also used extensively in construction as infill in the frame structure and as partition walls.

The masonry would continue to be used in the low to medium rise buildings because of its

low cost, environmental insulation and good vertical and lateral load resistance. However,

due to significant deviation from the decades old earthquake resistant traditional construction

and the use of non-engineered construction in urban nuclei, the seismic hazard posed by

masonry has alarmingly increased.

In the recent 2005 Kashmir earthquake more than 450,000 buildings were partially or fully

damaged (ADB-WB, 2005). Most of the buildings were non-engineered, un-reinforced

masonry, including adobe, rubble stone, concrete block and brick masonry buildings. Most of

the deaths and injuries were the direct results of collapse of buildings. Structural

configurations, low quality of masonry materials, workmanship and lack of confinement of

the masonry walls were responsible for the widespread building damage (Naseer, A., et al,

2009). The Kashmir earthquake proved that un-reinforced masonry buildings are vulnerable

in moderate and high seismic zones. However, the need for earthquake resistant construction

has been realized by the people and because of that in the post-earthquake scenario

construction of confined masonry single to triple story buildings has increased many folds.

The construction currently being practiced is considered to be non-engineered as no proper

analysis and design has been carried out.

The seismic analysis and design of masonry buildings require parameters of dynamic

behavior. Modern seismic building codes like Eurocode and Uniform Building Code (UBC)

2

gives these provisions. Immediately after the Kashmir earthquake, Pakistan Building Code

was developed by modifying modern international seismic building codes, for example the

Uniform Building Code (UBC 97), American Concrete Institute (ACI) and American

National Standard Institute (ANSI). However, the development of indigenous design

parameters is needed for their onward incorporation in the Pakistan Building Code.

The seismic behavior of masonry buildings depends on the configuration of buildings,

mechanical properties of masonry materials and assemblage, and workmanship. Therefore,

the evaluation of seismic behavior of typical Pakistani masonry buildings and the design

parameters is required. In this research work seismic behavior of typical confined brick

masonry buildings has been evaluated by subjecting reduced scale models to increased

intensities of ground motions on uni-axial shake table.

1.2 AIM AND OBJECTIVES OF THE RESEARCH WORK

The proper understanding of behavior of typical masonry building requires the knowledge of

masonry materials and their assemblage. In order to investigate the non-linear seismic

behavior of buildings shake table testing has been preferred over the static testing. However,

large multi-degree-of-freedom shaking tables are developed to drive large masses, testing full

size specimens is limited because of the high cost of operation and testing specimen. Reliable

test data is obtained by testing reduced scale building models on simple earthquake

simulator. Generally, global behavior of the building models is determined. Following are the

objectives of this research work:

• Seismic evaluation of typical confined brick masonry buildings,

• Evaluation of response modification factor and ductility ratio of typical confined

brick masonry buildings

• Determination of properties of typical masonry materials

• Evaluation of properties of typical masonry assemblage

The research addresses some of the goals of the Earthquake Engineering Center (EEC) to

develop indigenous design parameters for Seismic Building Code of Pakistan and improve

the current construction practice and earthquake engineering in Pakistan.

3

1.3 SCOPE OF WORK

Scope of this research work includes evaluation of the behavior of typical confined brick

masonry buildings by shake table testing of single and double story models and to provide

values of the response modification factor and ductility ratio of the typical confined brick

masonry buildings.

Evaluation of the properties of prototype masonry materials and assemblages in compression,

tension and cyclic loading was carried out. The testing of the model masonry materials and

assemblages to simulate the prototype masonry properties were also carried out.

1.4 RESEARCH METHODOLGY

The experimental programs of this research work have been divided into following phases:

• In the first phase, prototype masonry materials and assemblage have been tested to

determine their mechanical properties. Test data of bricks and reinforcing bars was

collected from the material testing laboratory of the university and analyzed to

evaluate typical properties of masonry materials. Masonry mortar samples from the

on-going construction in Peshawar, Abbottabad and Mansehra have been collected

and tested in compression. Prototype masonry assemblages were prepared from

typical materials and tested in compression, diagonal compression and, constant

vertical and cyclic lateral load.

Mortar used for the prototype masonry assemblage is typical mortar used in and

around Peshawar city, i,e., cement-sand-khaka (stone dust) mortar in the proportion

of 1:4:4 by volume. Cement-sand mortar in the proportion of 1:6 and 1:8 is also

common in Peshawar and earthquake affected area. Data collected from the material

testing laboratory represents lager part of N-W.F.P.

• In the second phase extensive research has been carried out to simulate masonry

materials properties (compressive strength of mortar and concrete, and compressive

strength and density of brick). Cement-lime-sand and cement-lime-surkhi (broken

bricks) mortar was used for preparation of model masonry mortar, micro-concrete and

model bricks. Different mixes of mortar for model masonry mortar, micro-concrete

4

and model bricks have been prepared and tested in order to obtain physical and

mechanical properties of model materials, conforming to the requirement of the

theory of models. Model masonry assemblages (model prisms and wallets) have been

tested to evaluate their strengths in compression and tension. Model walls have also

been tested in static lateral load.

• In the final phase, typical model buildings have been fabricated and tested by

subjecting them to increasing intensity of shake table motion in each test run.

Response accelerations and displacements were measured at floor levels. The data has

been analyzed to determine response modification factor.

1.5 REPORT ORGANIZATION

The report contains collection and analysis of materials data, testing of masonry assemblage

and shaking table test of typical confined brick masonry building models. The report has

been divided in to six chapters and is presented in the following manner:

Chapter 2 presents literature review. The chapter is divided into seven sections. Typical

properties of Pakistani masonry materials are presented. Failure mechanism and behavior of

confined masonry buildings during past earthquake all over the world is presented.

Provisions of codes about the confined masonry buildings are discussed. The background of

similitude laws is described. Finally the research work carried out elsewhere in the world on

shake table and cyclic test of walls are reviewed in this chapter.

Chapter 3 contains the testing of prototype and model masonry. Compressive strength and

water absorption of masonry units used in this research work is presented. Compressive

strength, shear strength and cyclic test of prototype masonry conducted are also presented.

The results of modeling of masonry materials and testing of model wallets constructed to

simulate the physical and mechanical properties of prototype masonry walls are analyzed and

discussed.

In chapter 4, layout of typical Pakistani single and double story masonry buildings are

selected by analyzing number of drawings. Fabrication of the models is discussed. Additional

5

masses required for simulating floor masses is determined. Instrumentations of the models

and testing procedure are also presented.

In chapter 5, results of the shaking table test are presented. The failure mechanism observed

during the shaking table test is discussed. Frequency and damping ratio measured during

different intensity of shaking is also presented. Base shear and drift ratio measured for single

and double story building is provided. Response modification factor calculated for single and

double story typical confined brick masonry are presented.

Chapter 6 presents summary and, conclusions and recommendations of the research work.

Future research works have been recommended.

6

CHAPTER 2 LITERATURE REVIEW

2.1 INTRODUCTION

Confined masonry is one of the most widely used construction systems in Latin America,

Europe and Asia. Where, the masonry system performed satisfactorily during past

earthquakes. The system has been in use for decades; however, not much experimental work

has been done for the evaluation of behavior of confined masonry. In Pakistan, confined

masonry construction is popularly used after October 08, 2005 Kashmir earthquake through

the affected area.

In this chapter an attempt has been made to present typical properties of masonry materials

used in Pakistan in section 2.2. The data presented here represent mainly N-W.F.P. However,

data of bricks and steel bars is collected from Material Laboratory of Department of Civil

Engineering and is supposed to cover much larger area than N-W.F.P. The failure mechanism

of the confined masonry is discussed in section 2.3. The behavior of confined masonry

buildings during past earthquakes in Latin American and Asian countries is presented section

2.4.

Section 2.5 presents code and guidelines recommendations about confined masonry

materials and structural requirements.

Section 2.6 provides theoretical background of similitude requirements in testing reduced

scale masonry models.

The experimental research carried out at different research institute including shaking table

tests of reduced scale models and cyclic test of walls is presented in section 2.7.

7

2.2 PROPERTIES OF PAKISTANI MASONRY

2.2.1 Masonry Unit

Burnt clay brick, sun dried clay brick (adobe brick), solid concrete block and, dressed and

undressed stone is used as masonry unit for the construction of masonry buildings in

Pakistan. In the subsequent section physical and mechanical properties are given for masonry

units. Brick data collected from Materials Laboratory, Department of Civil Engineering, N-

W.F.P UET, Peshawar has been analyzed and presented.

2.2.1.1. Brick

In the urban center solid burnt clay bricks are mostly used in the masonry building

construction and as masonry infill in the frame structures. However, in the rural areas adobe

bricks, of same size as burnt brick, are also used for the construction of single story

residential houses. The clay bricks are manually produced by pressing clay with certain

amount of sand in the wooden mould (figure 2.1). The wet bricks are first dried in the sun

and air and then transported to the brick kiln for subsequent burning process. The bricks are

burnt up to temperature of 800-900 C° in the brick kiln. As there is no temperature control in

the kiln, three different types of bricks are normally produced. The bricks are categorized as

first class with sharp edges, have comparatively low absorption and good strength. The first

class brick are recommended bricks type for building construction. The second class brick

are porous under-burnt with relatively high absorption and low strength. These types of

bricks are preferably used by low income group for construction of residential buildings. The

other types of bricks are over burnt with dark brownish color and irregular shape. These

bricks are not used for construction purposes.

The physical and mechanical properties of burnt clay bricks are given in table 2.1 and table

2.2. Data of almost 500 bricks tested in the Material Laboratory, Department of Civil

Engineering, N-W.F.P UET, Peshawar has been analyzed. The dimensions given in the table

are actual dimensions measured before crushing of the brick in universal testing machine.

The compressive strength of brick has been determined on full size brick, properly capped on

both sides.

8

Figure 2.1 Adobe brick manufacturing and stacking for sun drying

Table 2.1 Physical and mechanical properties of burnt clay brick

Length

inch (mm)

Width

inch (mm)

Height

inch (mm)

Specific Weight

pcf (kN/m3)

Strength psi

(MPa)

Maximum 9.63 (245)

5.75 (146)

2.81 (71)

125.4 (19.7)

6017.0 (41.5)

Minimum 8.00 (203)

4.00 (102)

2.50 (64)

84.8 (13.3)

617.0 (4.2)

Mean 8.71 (221)

4.21 (107)

2.71 (69)

98.1 (15.4)

2350.0 (16.2)

Coefficient of variation (%) 2% 3% 3% 22% 30%

Table 2.2 Absorption of burnt clay brick

Wet weight

lb (N)

Dry weight

lb (N) Absorption (%)

Maximum 6.98 (31.0)

7.95 (35.4) 25.84

Minimum 4.86 (22.0)

6.04 (27.0) 7.79

Mean 5.90 (26.0)

7.02 (31.0) 18.88

Coefficient of Variation (%) 37% 42% 18%

It is observed that the variability in the compressive strength as well as specific weight of the

solid burnt brick is quite large. The variation in strength and weight could be attributed to

raw materials, sun drying and burning temperature. However, it has been found from the

9

statistical evaluation of the compressive strength of masonry units in Latin America that hand

made solid clay bricks strength depended on the raw materials used in the fabrication and not

on the fabrication process itself (Alcocer, S.M., and Klingner, S.M 1994). It can be seen that

the mean compressive strength comply with the minimum strength (1000 psi or 6.89 MPa)

required by Earthquake Rehabilitation and Reconstruction Authority (ERRA) guidelines and

European standard (EN 771-1).

The absorption of brick is not directly affecting quality of masonry; however, bricks absorb

water from mortar and render the masonry weak.

2.2.1.2. Block

Solid concrete block is also becoming popular, especially in the northern part of N-W.F.P or

Azad Kashmir because of the unavailability of brick kiln and high cost of brick imported

from other part of the country. The blocks are used for construction of single or double story

buildings and also as infill masonry in the frame structure. The blocks are manufactured in

small factories in semi-automatic machines. Generally the mix proportion used for the

concrete is quite lean and there is no control of water to cement ratio. The ingredients are

mixed by volume in the proportion of 1:4:8 (one part of cement to four part of sand and eight

part of course aggregate), 1:4:6 and 1:5:7 by volume. The different sizes of blocks produced

are 12 x 8 x 6 inch (30.5 x 20.3 x 15.2 mm), 12 x 8 x 5 inch (30.5 x 20.3 x 12.7 mm) and 12

x 8 x 4 inch (30.5 x 20.3 x 10.1 mm) (length x width x thickness). Table 2.3 gives nominal

dimensions and average compressive strength of solid blocks collected from three different

factories. It is worth mentioning that the compressive strength given in table 2.3 is mean

value of three blocks, determined by testing full size unit normal to bed.

10

Table 2.3 Dimensions and compressive strength of concrete block

Length

inch (mm)

Width

inch (mm)

Height

inch (mm)

Average

Strength psi

(MPa)

1 12 (305)

6 (152)

6 (152)

220.0 (1.5)

2 12 (305)

8 (203)

6 (152)

906.0 (6.2)

3 12 (305)

8 (203)

6 (152)

750.0 (5.2)

Earthquake Reconstruction and Rehabilitation Agency (EERA) construction guideline-2006

recommends 12 x 8 x 6 inch (30.5 x 20.3 x 15.2 mm)concrete block for the construction of

building. However, the minimum compressive strength is not specified, the mix proportion of

one part of cement to three part of sand and three part of coarse aggregate (1:3:6) is specified.

The mean compressive strength of concrete block 12 x 6 x 6 (30.5 x 15.2 x 15.2) is less than

the minimum compressive strength specified in relevant European Standards (EN 771-1-6)

which is 261 psi (1.8 MPa). However, compressive strength of the concrete block 12 x 8 x 6

(30.5 x 20.3 x 15.2 mm) is more than the minimum compressive strength of both EN 771-1-6

and EC 8 for solid concrete aggregate units.

2.2.1.3. Stone

Stone masonry has been traditionally used in northern area of Pakistan. Use of un-dressed

stone units was more common in unreinforced masonry and in Dhajji type construction.

According to Eurocode 6 and Eurocode 8, the use of dimensioned stone units that are square

dressed units with parallel horizontal faces, is allowed for the construction of masonry

building in seismic zones.

2.2.2 Mortar

Mortar is used to bind masonry units, is a mixture of binding material (cement and/or lime),

aggregates (sand) and water. In the century old buildings when cement was a rare building

construction material, the mixture of lime and surkhi (burnt brick powder) were used as

mortar. The mix proportion and compressive strength of the lime-surki could not be

ascertained. With the advent of cement, the use of lime and surkhi become less significant,

11

probably, for their slow setting time. However, lime-surkhi mortar is still used for the repair

of old traditional and monumental buildings.

Mortar consisting of mixture of cement-sand and/or cement-sand-khaka (stone dust) is used

in the contemporary buildings construction. The constituent materials are manually mixed in

different proportions depending on the thickness of walls (that is double leaf full brick or

single leaf half brick wall), number of stories and economic class. The water is arbitrary

added to achieve workable paste. The addition of water and remixing with time is common

practice. Table 2.4 gives compressive strength of cement-sand and cement-sand-khaka

mortar collected from 30 under-construction building sites in Peshawar, Abbottabad and

Mensehra. The compressive strength is determined by testing 2 inch cubes specimens.

Table 2.4 Compressive strength of mortar collected from field

Compressive Strength, psi (MPa)

7 Days 28 Days

Maximum 1096.0 (7.6)

1680.0 (11.6)

Minimum 84.5 (0.58)

156.0 (1.1)

Mean 545.5 (3.8)

837.5 (5.8)

Cov (%) 102% 66%

It could be seen in table 2.4 that the variation in compressive strength of mortar is very large.

The low strength could be attributed to lean mix, use of high water to cement ratio and use of

mortar after it has been set. However, the mean compressive strength is higher than type M5

(725 psi/5 MPa) recommended by EC 8 for unreinforced and confined masonry. The scatter

of data could be attributed to mix proportion, w/c ratio, mix material and time of use of the

mortar.

2.2.3 Steel bar

In building construction, generally grade 40 (fy = 40 ksi) and grade 60 (fy = 60 ksi) bars are

used from #3 to #8 (0.375 to 1 inch diameter) deformed bars. However, plain bars have also

been used in the existing construction. #3 and #4 deformed bars are mostly used in reinforced

concrete slab in masonry buildings. #3 bars are also used for stirrups in beams and columns.

12

#4 and #6 bars are mostly used as longitudinal bars in beams. In table 2.5 and 2.6 simple

statistical analyses for yield strength, ultimate strength and elongation is presented. Data of

almost 1500 steel bars have been collected from Material Laboratory, department of Civil

Engineering, N-W.F.P UET, Peshawar and analyzed. The yield and ultimate strength given

in table correspond to grad 40 and grade 60 deformed bars.

Table 2.5 Characteristics of #3 (3/8 inch diameter) bar

Yield Strength

psi (MPa)

Ultimate Strength

psi (MPa)

Percentage

Elongation

(%)

Ultimate to

Yield Strength Ratio

Maximum 90,251.5 (622.5)

14,1628.4 (977.0) 22.66 2.45

Minimum 41,718.5 (288.0)

59,040.0 (407.0) 2.34 1.00

Mean 67,067.0 (462.5)

94,083.0 (649.0) 13.85 1.41

Cov (%) 15% 14% 25% 11%

Table 2.6 Characteristics of #4 (1/2 inch diameter) bar

Yield Strength

psi (MPa)

Ultimate Strength

psi (MPa)

Percentage

Elongation

(%)

Ultimate to

Yield Strength Ratio

Maximum 87478.5 (603.5)

130915.5 (903.0) 25.00 1.77

Minimum 40987.6 (283.0)

59938.8 (413.5) 2.34 0.94

Mean 66013.0 (455.0)

94591.5 (652.5) 15.72 1.44

Cov (%) 13% 12% 23% 7%

However, properties of grade 40 and grade 60 rebars could not be distinguished from the

data. The mean value of ratio of ultimate to yield strength is higher than 1.25 as required by

Section 1921.2.3.2 of Uniform Building Code 1997 (UBC 97). The mean elongation for both

#3 and #4 bars is more than the minimum required (9%) by ASTM A 615.

It has been concluded by a statistical study (Fakhur-us-Zaman 2003) that the probability of

obtaining yield strength between 55,000 psi/379.0 MPa and 85,000 psi/586.0 MPa for #3 and

13

#4 bars are 89.96 and 87.51 respectively, which reflects wide dispersion of yield strength

values of grade 40 bars from a specified minimum value of 40,000 psi/275.9 MPa.

2.3 FAILURE MECHANISM

In this section first the failure mechanism of un-reinforced masonry (URM) is discussed and

then the different modes of failure in the confined masonry, according to earthquake damage

analysis and experimental investigations are presented.

2.3.1 Un-reinforced Masonry

According to earthquake damage analysis and experimental investigation, four types of

failure modes have been identified. The crack patterns and failure mode of URM depend on

the axial stress, aspect ratio (height to width ratio), material strength and boundary

conditions.

• In the case of low vertical stresses and poor quality of materials, when the horizontal

shear stresses exceed the joint shear strength of the masonry, horizontal cracks at the

top and bottom of the pier develops. The upper part usually slides over the lower part

and the type of damage are called sliding failure (figure 2.2).

• Diagonal shear failure (figure 2.3) occurs where the principal tensile stresses, exceed

the tensile strength of the masonry. This is the most frequent type of failure mode.

The diagonal shear cracks either follow the mortar joint or passes through masonry

unit depending on the relative strength of mortar and unit.

• In the case of large flexure moment and improved shear resistance, horizontal cracks

at the top and bottom develop and the pier may undergo rigid body rotation (figure

2.4). This type of failure mode is known as rocking.

• The principal compressive stresses, sometimes, exceed the compressive strength of

masonry leading to crushing of masonry. As toe of the pier is usually the zone of high

compressive stresses, the crushing occurs at the toe and the failure is called toe

crushing (figure 2.4).

14

Figure 2.2 Sliding failure

Figure 2.3 Shear failure

15

Figure 2.4 Rocking failure and crushing of brick

The in-plane failure of pier is often the combination of the above failure modes. As the

nature of failures is different, so is their energy dissipation and deformation capacity. The

rocking exhibit large deformation but comparatively less energy is dissipated. Because of the

sliding action along the head and bed joint more energy is dissipated in shear failure.

However, diagonal cracks passing through units make the pier unstable and results in brittle

failure. Similar behavior of instability of pier could be expected during toe crushing.

Based on FEMA 307 (ATC 1999), the ultimate drift ratio for different mode of failure has

been summarized by Simsir C.C 2004. The pier failing in diagonal tension or toe crushing

without rocking or sliding, the ultimate drift capacity of pier is around 0.5%. While if rocking

and sliding failure is preceded by diagonal or toe crushing, the ultimate drift is larger from

1% to 2%. FEMA 274 provides the following formula for the elastic stiffness, Ke of

masonry piers based on elastic theory considering flexural and shear deformation:

α

=⎡ ⎤⎛ ⎞⎛ ⎞+⎢ ⎥⎜ ⎟⎜ ⎟

⎝ ⎠⎝ ⎠⎢ ⎥⎣ ⎦

21.2 1

we

GAK

G hhE L

(2.1)

Where:

16

Aw = horizontal area (length, L x thickness, t) of the wall.

α = coefficient determining the position of the inflection point along the height of pier

(α = 0.83 for fixed-fixed wall and 3.33 for cantilever wall)

h = height of the pier

The tensile strength, ft of masonry wall can be calculated from the theory of shear resistance

as (Turnsek and Cacovic, 1971):

( )στ°⎛ ⎞= +⎜ ⎟

⎝ ⎠21.5

2tf (2.2)

Where:

σ° = compressive stresses in the pier,

τ = Shear stresses in the pier.

2.3.2 Confined Masonry

Confined masonry is one of the widely used masonry systems in Latin America, Asia and

Europe. In this type of masonry system un-reinforced masonry wall are confined with

horizontal and vertical reinforced concrete elements or reinforced masonry elements (figure

2.5). The confining vertical elements, which are also known as tie columns, are provided to

improve the ductility and seismic resistance of building and prevent disintegration of

masonry walls during strong ground motion. The horizontal confining elements or bond

beams are used to make sure the box type behavior by tying all walls together. In confined

masonry, walls are erected first and then concrete is poured at the location of tie columns and

bond beams. The confining elements are not designed to resist any load. According to

Eurocode 6 and 8, no contribution of the confining elements should be taken in the

verification of confined masonry buildings. However, in the case of reinforced concrete

frame structure, columns and beams are part of the load resisting structure system. In frame

structure columns and beams skeleton is first constructed and it is then filled with masonry

walls. In order to be efficient construction, the bond beams and tie columns reinforcements

17

should be properly connected and anchored. Toothing should be provided at the vertical

border of walls for proper interaction of masonry walls and tie columns.

The different types of failure modes observed during earthquakes and in experimental studies

of confined masonry are classified as in-plane, out of plane and connection failure. The

evidence of observed behavior has been given; however, detailed description of experimental

testing and damage during earthquakes are provided in the subsequent sections.

Figure 2.5 Confined masonry walls

2.3.2.1. Plane Failure

The three different types of in-plane failure in the confined masonry are diagonal shear

failure, sliding shear failure and flexure failure.

• Confined masonry transfer horizontal in-plane inertia loads by diagonal strut (figure

2.6) from the upper floor level to lower floor level or to the foundation. When the

principal diagonal tensile stresses, produced by diagonal compression stresses, exceed

the tensile strength of masonry, diagonal cracks appear in the masonry. In the case of

weak mortar and strong unit, the cracks follow mortar joint in zig zag fashion and if

the unit is comparatively weak, diagonal cracks passes through masonry unit. When

the deformation continues to increase, eventually, shear cracks also appear in the

vertical confining column at the top joint. The factors which are responsible for this

type of failures are low tensile strength of mortar and weak mortar-unit bond strength.

Uniformly distributed diagonal shear cracks develop and propagate towards tie

column, thereby cracking the reinforced column. Crushing of masonry units in the

18

middle part of masonry and crushing of tie column concrete were observed at high

stress demand (Tomazevic, M., 1997; Ishibashi, K., et al. 1992). It has also been

observed during past earthquakes and in experimental studies that diagonal cracks

concentrate in the ground story (Alcocer et al., 2004; Schultz, A.E., 1994; EERI

2007).

Figure 2.6 Internal forces direction in confined masonry building to lateral load

• Sliding shear failure is the second type of in-plane failure observed in the confined

masonry buildings. This type of failure occurs in horizontal plane by the shear failure

of weak mortar brick bond. The cracks also sometime extend to vertical confining

element. Sliding shear failure are associated with the diagonal cracks.

• The third type of failure is the flexure failure. In the case of tall wall and high lateral

seismic load, large bending moments are produced at the bottom of the wall, thereby

producing tensile stresses at the one and compression stresses at the other end of the

in-plane confined wall. When the tensile stresses exceed the tensile strength of

mortar, horizontal cracks appear as shown in figure 2.7. Separation of vertical

confining element and masonry walls, and horizontal cracks in the vertical confining

element sometimes also follow.

19

Figure 2.7 Flexure cracks in confined masonry

2.3.2.2. Connection failure

Different type of connection failures are separation of masonry wall from vertical confining

element, separation of diaphragm/bond beam and masonry wall, and joint failure of

horizontal and vertical confining elements. The connection failure results in the change in the

mechanism of the masonry. The masonry walls are no longer be able to transfer tensile

stresses to vertical confining element.

• The masonry wall and vertical confining element separation could result by in-plane

or out of plane forces. This type of failure affects in-plane behavior by preventing

transfer of tension forces from the wall to the column. The failure also affects out of

plane behavior as the masonry walls are no longer supported by confining elements.

Separation of tie column and wall (figure 2.8) has been observed during earthquakes

and confined masonry testing (Paikara, S. and Rai, D.C, 2006; Yoshimura et al.,

2004; Yoshimura, K., and Kuroki, M., 2001).

• The second type of connection failure is also the result of either in-plane or out of

plane loadings. The failure results in weakening out of plane resistance and in-plane

load transfer. Horizontal cracks between floor slab and masonry wall were observed

during the 1985 Chile earthquake (Schultz, A. 1994).

• Improper anchorage of reinforcement at the confining elements joint results in the

joint failure.

20

Figure 2.8 Separation of confining element and masonry wall (Yoshimura et al., 2004)

2.4 RESPONSE OF CONFINED MASONRY DURING EARTHQUAKES

In this section, the observed behavior of confined masonry during earthquake is presented. It

has been observed that properly designed confined masonry performed satisfactorily well

during earthquakes. However, some of the buildings were severely damaged. The poor

performance of building was attributed to insufficient confinement provided to the masonry

walls, inadequate diaphragm connections, discontinuous tie beam and inappropriate

structural configuration. In the following section the experiences during Asia and Latin

American major earthquakes are given. The behavior of confined masonry during

earthquakes up to 2000 is presented in section 2.4.4.

2.4.1 Bam Earthquake (26 December 2003)

On 26 December 2003 at about 1:57 GMT, the historical city of Bam, Iran was struck by

strong earthquake, Ms of 6.7. Forty five thousand people lost their lives. PGA of 0.8g and

0.7g for the East-West and North-South horizontal components, respectively, were recorded

in the Bam station. The masonry buildings consisting of load bearing burnt brick masonry

with steel roof were as poor as adobe buildings. However, newly constructed masonry

buildings with vertical and horizontal reinforcing concrete elements performed well and

saved the lives of inhabitants (Zahrai, S. M., Heidarzadeh, M., 2004). Figure 2.9 shows a

confined masonry building damaged at opening during the earthquake. The collapse of

façade wall is also shown in the figure.

21

Figure 2.9 Damage to confined masonry building at opening (right side).

2.4.2 Peru Earthquake (August 15, 2007)

An earthquake of magnitude 7.9 struck Pisco, Peru at 6.40 p.m. local time, killing at least 519

people and injuring 1090. The modern properly engineered buildings found were the

confined masonry buildings. This type of construction consists in constructing first the clay

brick walls while leaving empty space with reinforcement which is latter filled in by

concrete, obtaining a solid joint between the RC frame and the clay bricks. In this way the

stiffer masonry walls provide most of the lateral resistance than the skeleton frame structure.

This type of building performed satisfactorily. The good performance of confined masonry

brick building up to six stories (figure 2.10) may be because of their inherent large capacity

to lateral loads (Sventlana Brzev 2007). Figure 2.11 shows undamaged two story building

next to collapsed adobe building (EEFIT report 2008). Confined masonry with soft stories

and other irregularities as well as bad detailing was severely damaged (figure 2.12).

However, well constructed confined masonry resisted the earthquake with little or no damage

(EERI report Oct 2007).

22

Figure 2.10 Undamaged six stories confined masonry building in Ice during 15 August, 2007

Peru earthquake (Sventlana Brzev 2007)

Figure 2.11 Undamaged two storeys RC confined masonry building next to a collapsed

adobe house in Ica (EEFIT 2008)

23

Figure 2.12 Collapsed confined masonry due to soft stories (EERI 2007).

2.4.3 Central Java Earthquake (May 17, 2006) and Sumatra Earthquake (December 26, 2004)

On May 27, 2006 at 5.54 am local time an earthquake of magnitude 6.3 struck Java islands,

Indonesia leaving 5,176 people dead. An estimated 154,000 houses were completely

destroyed and 260,000 suffered damage of different nature. The houses in the affected area

were divided into unreinforced masonry, confined or partially confined masonry and timber

frame houses. The post 1990 construction include confined or partially confined brick, solid

concrete block or stone masonry in cement mortar walls with flexible, pitched or hipped

timber truss or bamboo roofs covered by clay tiles. The confined masonry building

performed well (EERI 2006) in this earthquake.

In the town of Banda Aceh Sumatra, Indonesia confined masonry buildings constituted 70%

of the housing stock. During 2004 Sumatra earthquake, the buildings 1-2 stories high did not

collapse; however, ground story walls experienced out-of-plane failure by tsunami-induced

water pressure.

2.4.4 Earthquakes in American continent (up to 2000)

Observation made during past earthquakes in the North, Central and South American

countries are discussed. Generally, it has been observed that lightly loaded and regular

confined masonry performed quite well during earthquakes, particularly for one and two

24

story residential buildings. Construction deficiencies and poor quality of construction

materials were the causes of poor performance of confined masonry.

The performance of confined masonry up to four or five stories were generally good during

1985 Mexico earthquake (Mw 8.0). However, complete collapse of a three story office

building with a highly irregular floor plan was observed (Schultz, A. 1994). In the 1999

Tehuacan (Mw 6.5) and 2003 Tecoman (Mw 7.6) earthquakes, confined masonry buildings

performed generally well. However, some failures were observed due to inadequate wall

strength, poor quality of construction, inadequate number and arrangement of confining

element (figure 2.13) (EERI, 1999 & 2006).

Figure 2.13 Damage confined masonry building (1999 Tehuacan earthquake) due to non-

confinement in window (EERI, 1999)

On January 13, 2001, an earthquake of magnitude Mw=7.7 occurred in the Republic of El

Salvador in Central America. The earthquake resulted in 844 people dead and 75,000

buildings completely damaged. The use of ‘confined masonry’ walls is more popular for the

construction of residential buildings. In this system, cast-in-place, slender R/C columns are

presented at most of the extreme edges and intersections of the walls. In addition, cast-in-

place R/C collar beams are also provided. Buildings up to three and more stories are used.

The large number of existing confined masonry buildings were not severely damaged during

the earthquake, except in few cases of shear failure and separation of block masonry wall and

vertical confining column (Yoshimura, K., and Kuroki, M., 2001). It was reported by

25

Ascheim et al (2006) that ‘mixto’ confined masonry construction was used in the post-

earthquake rehabilitation following the 2001 earthquakes.

It was observed during March 31, 1983 Popayan, Colombia earthquake that adding

horizontal beams to unreinforced masonry reduced the seismic damage, while the addition of

tie column eliminate damage (Schultz, A. 1994). In the 1999 El Quindio, Colombia

earthquake (Mw 6.2), shear cracks and out of plane failure because of the inadequate

connection between wall and confining elements was observed (EERI, 2000).

The 1985 Llolleo, Chile earthquake (Mw = 7.8) caused the collapse of 66,000 buildings and

damaged upto 127,000. Out of 84,000 housing units, 13,500 were of confined masonry. The

buildings were from 3 to 5 storeys in height (Sventlana Brzev 2007). Confined masonry in

Chile has generally performed well during earthquakes; however, elimination of tie column

for economic purposes lead to the extensive inclined cracking and horizontal cracks between

floor slabs and masonry wall were observed during the 1985 Chile earthquake (Schultz, A.

1994). In the figure 2.14 below complete wall panel collapsed, after first developing diagonal

shear cracks. The tie columns can also be seen damaged.

Figure 2.14 Damaged confined masonry during 1985 Llolleo, Chile earthquake (Moroni et

al., 2003)

Damage to short residential confined masonry was observed due to structural configuration

and omission of tie members during 1990 Pomasqui, Ecuador earthquake (Schultz, A. 1994).

26

2.5 CODES /GUIDELINES RECOMMENDATIONS

The use of confined masonry has been practiced in Latin America, Asia and Europe. In most

of these countries the specification for confined masonry is part of their code or country

guidelines. The specifications are developed after experiences during the past earthquakes

and extensive experimentation. It has been observed that the confined masonry improves

both ductility and seismic resistance of the structure. In the subsequent sections, the

specifications of different codes and guidelines are discussed.

2.5.1 Specifications of Eurocode 6 & 8

According to the requirements of Eurocodes, no contribution of vertical confinement to

vertical and lateral resistance of the structure should be taken into account in the calculation

(C1.4.9, EC 6). Eurocode 6: Design of masonry structures gives some basic rules for the

confined masonry as discussed below; however, some additional requirements have been

specified in Eurocode 8: Design provisions for earthquake resistance of structures.

2.5.1.1 Construction Technique

According to Eurocode reinforced concrete or reinforced masonry vertical (tie column) and

horizontal (bond beam) confining element should be provided to the masonry wall so that

they act together during lateral action. Concrete for confining elements should be cast after

the construction of masonry wall. The confining elements should be provided at the

following locations:

• At all free edges of the structural walls,

• At the walls intersection,

• Tie columns should be placed at a maximum spacing of 13 ft (4 m) and,

• At both sides of opening having an area of more than 16 sft (1.5 m2)

• Tie beams should be provided at every floor level and at a vertical spacing of 4 m.

27

2.5.1.2 Geometric requirements in the confining masonry and area of reinforcement

The confining element should have cross-sectional area of 31 in2 (0.02 m2), with minimum

dimension of 6 inch (150 mm) in plan of the wall. In the case of double leaf wall, the

confining element should be equal to the wall thickness. The minimum wall thickness is the

one which give robust wall or determined from calculations.

The longitudinal reinforcement should be 0.8 % of the cross-sectional area of the confining

element and should not be less than 0.31 in2 (200 mm2). The stirrup should not be less than #

2 (6 mm) bar and should be provided at least at 12 inch (300 mm).

Horizontal reinforcement not less than # 2 (6 mm) diameter bars or equivalent and spaced at

12 inch (300 mm) should be provided and anchored in concrete column and in the mortar

joints.

According to additional requirements in Eurocode 8 (section 9.5.3), the minimum area of

reinforcement is 0.5 in2 (300 mm2) or 1% of the cross-sectional area of the confining

element. The stirrup should be provided at 6 inch (150 mm) center to center. The bar

diameter mentioned in Eurocode 8 is 5 mm which is slightly less #2 bar. The bars should be

spliced at length of 60 times diameter of bar.

The minimum thickness of the wall should be 9.5 inch (240 mm). The minimum effective

height to thickness ratio of the wall should be 15 and length of wall to clear height of the

opening (adjacent to the wall) should be 0.3.

2.5.1.3 Material Strength

The minimum compressive strength of masonry mortar of 730 psi (5 MPa) should be used

for confined masonry buildings.

2.5.1.4 Number of stories and wall density ratio

Eurocode 8 recommends minimum number of stories depending on the seismicity of the area

and wall density ratio. Table 2.7 gives the number of stories corresponding to minimum wall

density ratio and the maximum ground acceleration. In the table, k is a corrective factor

based on minimum unit strength of 725 psi (5 MPa) for confined masonry. Where k = 1+(lav-

28

2)/4≤2 for buildings having 70% of the shear walls under consideration are longer than 6.5 ft

(2 m), however, for all other cases k = 1. In the expression lav is average wall length.

Table 2.7 Recommended allowable number of stories above ground and minimum area of

shear walls for simple buildings (EC 8)

Acceleration at

site ≤ 0.07 k.g ≤ 0.10 k.g ≤ 0.15 k.g ≤ 0.20 k.g

No of Stories Minimum sum of cross-sections areas of horizontal shear walls in each direction,

as percentage of the total floor area per storey

2 2.0 % 2.5 % 3.0 % 3.5 %

3 2.0 % 3.0 % 4.0 % N/A

4 4.0 % 5.0 % N/A N/A

5 6.0 % N/A N/A N/A

2.5.2 Additional Recommendations

However, detailed and through discussion on the earthquake resistance of masonry buildings

has been given, some additional recommendations regarding confined masonry have been

provided in addition to Eurocode specifications by (Tomazevic, M., 99). The information has

been based on actual observation of masonry during earthquake and experimental research

work carried out by the author.

Because of the lack of experimental work on the behavior of confined masonry, the amount

of reinforcement in confining element is determined on empirical basis. Table 2.8 gives

number of plain bars depending on the number of stories and seismic demand.

29

Table 2.8 Typical reinforcement of vertical confining element

No of Stories

Seismic Demand

Low

(PGA = 0.1 g)

Moderate

(0.1 g < PGA < 0.2 g)

High

(0.2 g < PGA < 0.4 g)

2 1-2 4-8 mm bars 4-10 mm bars (4#3) 4-12 mm bars (4#4)



6 1-2 4-10 mm bars (4#3) 4-12 mm bars (4#4) 4-14 mm bars (4#4)



In order to fully utilize the resistance and energy dissipation capacity of masonry, the

masonry walls should be horizontally reinforced. Specially shaped ladder-type or truss type

reinforcement should be used in horizontal mortar joint provided at vertical spacing of 24

inch (600 mm). The horizontal reinforcement should be anchored in the tie column. In such

case the EC 8 requirements for connecting tie column and masonry wall should be waived

(Tomazevic, M., 99).

The seismic resistance of the masonry buildings should be verified, however, the number of

stories and height has been recommended in table 2.9 on the basis of masonry materials, wall

density ratio and configuration of building.

30

Table 2.9 Recommended maximum building height and number of stories (n)

Design ground acceleration < 0.2 g 0.2-0.3 g ≥ 0.3 g

Unreinforced

Masonry

Height, ft (m) 39.4 (12.0) 29.5 (9.0) 20.0 (6.0)

No of stories, n 4 3 2

Confined

Masonry

Height, ft (m) 59.0 (18.0) 49.0 (15.0) 39.5 (12.0)


Reinforced

Masonry

Height, ft (m) 79.0 (24.0) 69.0 (21.0) 59.0 (18.0)


Concrete of minimum compressive strength of 2,200 psi/15.2 MPa (C15) is recommended

for confined masonry elements.

It is also emphasized that the configuration of the building should be simple and regular. That

is the load bearing wall should be symmetrically distributed and should not change their

position and shape along the height of the building. A detailed description is presented in

(Tomazevic 1999) about the configuration or architectural requirements.

2.5.3 Confined Masonry Guidelines

Different confined masonry guidelines are available including City University guidelines

(Virdi and Raskkoff), Catholic University of Peru (PUCP and SENCICO, 2005), the

International Association of Earthquake Engineers (IAEE) (IAEE and NICEE, 2004), and

UNESCO (Ghaidan, 2002). The guidelines are in agreement on many points. However, there

are a few points where the guidelines have some differences. Some of the guidelines have

detailed approach and discuss comprehensively all the points, while the others are very

specific. A detailed discussion on the different guidelines and item by item comparison are

given in (UBC EERI Student Chapter, 2008 report). It has been tried to evaluate the

guidelines in the light of current research on confined masonry. It was concluded that Peru

guidelines could be used. However, recommendations were provided for the improvements

in the Peru guidelines.

31

Earthquake resistant confined masonry reports (Svetlana Brzev, 2007) discusses the different

requirements of confined masonry building construction. The report discusses different

factors which affect the seismic resistance of confined masonry. Confined masonry

performance during earthquakes is presented. Chile: NCh2123.97, Mexico: Mexico City

Building Code (NTC-M 2004), Eurocode 6 & 8 and Iranian code of practice for seismic

resistant design of building (Standard 28000) are summarized. Finally, the architectural and

construction guidelines are presented. It has been concluded that confined masonry generally

performed well; however, good quality materials and simple architectural design should be

used.

2.6 THEORY OF STRUCTURAL MODEL

A structural model is defined as any structural element or assembly of structural elements

built to reduced scale which is to be tested, and for which laws of similitude must be

employed to interpret test results (Harris.G and Sabnis 1999). Any structural model must be

fabricated, loaded, tested and results interpreted according the laws of similitude

requirements. Dimensional analysis is used to determine the similitude requirements of

physical quantities of model and prototype structures. The following relationship should be

satisfied for the different physical quantities involved in the structural modeling:

p m FQ Q x S= (2.3)

Where Qp is any physical quantity required, Qm is the physical quantity measured on the

model and SF is the scale factor corresponding to the physical quantity. The different types

of models used in the experimental analysis of masonry buildings depend on the materials

used for the fabrication of the models (Tomazevic. M and Velechovshky. T 1992)

1. In the case of complete model similarity special model materials are used for the

manufacturing of model. In such cases stresses are scaled to the geometric scale.

However, strain remains the same in the prototype and model (figure 2.15 (a)).

Specific weight, poisson’s ratio and damping are also same for model and prototype.

32

2. When prototype materials are used for the construction of model, the similarity is

called simple model similarity. In such case stress and strain are similar in both

prototype and model as shown in figure 2.15 (b).

Figure 2.15 Stress-strain relationship of model and prototype materials in the case of

complete model similarity

The physical quantities involved in the dynamic testing of masonry structure with

theoretically obtained scale factor fulfilling simple and complete model similitude

requirements are given in table 2.10.

StressStress

Strain

33

Table 2.10 Similitude requirements in dynamic testing

Quantity General equation Scale Factor

Complete model Simple model

Length (L) SL = Lp/Lm SL SL

Strain (ε) Sε = εp/εm 1 1

Strength (f) Sf = fp/fm SL 1

Stress (σ) Sσ = fp/fm SL 1

Young's modulus (E) SE = Sσ/Sε SL 1

Sp. Weight Sr = rp/rm 1 1

Force (F) SF = SL2Sf SL

3 SL2

Time (t) St = SL√(SrSε/Sf) √SL SL

Frequency (Ω) SΩ = 1/St 1/√SL 1/SL

Displacement (d) Sd = SLSε SL SL

Velocity (ν) Sv = Sε√SfSr √SL 1

Acceleration (a) Sa = Sf/SLSr 1 1/SL

The scale factor of 7 is upper limit for complete model in modeling brick or block masonry

and 4 for stone-masonry buildings (Tomazevic 1992). It is important in the dynamic testing

of model that dynamic behavior as well as failure mechanism is correctly simulated. Similar

distribution of masses and stiffness is required in the prototype and model building for

fulfilling similarity of dynamic behavior. And similar working stress level in the load bearing

walls of the prototype and model should be achieved for the similarity in failure mechanism.

Both requirements of dynamic behavior and working stress are fulfilled in following

complete model similitude requirements. However, special arrangements are required for the

mass distribution and working stress level, in case of simple model requirements.

2.7 EXPERIMENTAL TESTING

In this section experimental testing on shake table and cyclic testing of confined masonry

walls are briefly presented.

34

2.7.1 Shaking Table Test on 24 Simple Masonry Building (D.Benedetti, 1998)

A total of 14 shaking table tests were carried out in the ISMES (Seriate, BG, Italy) and LEE

(Laboratory for Earthquake Engineering, NTUA, Athens, Greece). The tests were carried out

on 1:2 scaled models. Actual prototypes materials were used in the model buildings. The

acceleration and stress scales were, respectively, Sa = 1 and Sσ = 1. As same materials were

used for models and real buildings, additional masses were applied to the model to respect

the scale.

Bricks and stones were used for the construction of model buildings. Intentially, low strength

mortar and low quality workmanship were used to simulate the field situation. The models

were subjected to base excitation in three translation directions. The vertical component was

70 % of the horizontal component. After damaging the models, different techniques were

used to repair and strengthen it.

It was concluded on the basis of analysis of the test results that lateral resistance increases for

both brick and stone masonry model after strengthening. Total collapse could be avoided by

using horizontal ties.

The values of the reduction factor ‘q’ are in general slightly higher for stone masonry than

for brick masonry. ‘q’ value for both the cases is 1.5 times higher than the code

recommended values. Strengthening increased such values in some instances by a factor up

to 1.8.

2.7.2 Verification of Seismic Resistance of Confined Masonry Buildings (Tomzevic, M., 1997)

Two models of a typical three story confined masonry buildings have been tested on shaking

table at Slovenian National Building and Civil Engineering Institute (ZAG) in Ljubljana,

Slovenia. The models were scaled at 1:5, conforming to the requirements of EC-8 for simple

buildings in plan. They were subjected to a series of simulated seismic ground motions with

increased intensity of shaking.

The structural system consisted of perimetral and internal walls in both orthogonal directions

dividing the plan into four rectangles. All the perimeteral walls and an internal wall in shorter

35

direction were pierced with window and door opening. Wall to floor area was 5% in both

orthogonal directions.

Diagonal cracks were observed in all stories at maximum resistance state. Crushing of

concrete and rupture of reinforcement of tie-column was also observed at the ultimate state.

It could be concluded from the tests results that prototype buildings would withstand, with

moderate damage to all walls, strong earthquakes with peak ground acceleration of 0.8g and

withstand without collapse a sever earthquake of PGA more than 1.3g.

The value of behavior factors ‘q’ was 2.91 and 2.47 for M1 and M2 models, respectively. It

could be concluded that confined masonry buildings possess more energy dissipation

capacity than code proposed values; however, taking into account the drift limitation of story

the codal values seem reasonable. Comparing ‘q’ values from previous research on un-

reinforced and reinforced masonry buildings of similar configuration and size, EC8

underestimate their energy dissipation capacity. However, further experimental and

analytical research is needed on response modification factor.

2.7.3 Shaking Table Tests of Small-Scale Model of Masonry Building: Advantages and Disadvantages (Tomzevic, M., 2000)

In this article, experiences of reduced scale shaking table test in context of advantages and

disadvantages have been discussed. It is emphasized that significant development has been

made in the numerical techniques and numerical models; however, experimental testing of

structures and sub-assemblages is needed. Seismic behavior of buildings could be determined

by cyclic test of walls, variability in the masonry need to test complete structural system.

Similitude in the dynamic behavior as well as failure mechanism of prototype and model is

considered important factor in modeling. Distribution of masses and stiffness in the prototype

and models need to be simulated. However, the failure mechanism requires similar working

stress level that is, working stresses in load bearing walls and compressive strength of

masonry of prototype and model. Although all the structural details are not precisely

modeled, the global seismic behavior of prototype building could be accurately simulated if

the behavior of model wallets is similar to prototype. Mechanical properties such as

36

compressive strength, tensile strength, ductility and energy dissipation, are simulated in

testing walls.

It is concluded that reliable information as regards the global seismic behavior and failure

mechanism can be obtained by testing small scale models of buildings on simple earthquake

simulator, although neither the physical models nor the seismic ground motion are modeled

in great detail. Special model materials for complete or prototype materials for simple model

can be used for the construction of the models. Scale factor 7 and 4 has been found as the

practical upper limit for modeling brick and block masonry, and stone masonry respectively.

In the case of complete model the requirements of dynamic behavior and failure mechanism

is automatically fulfilled. However, special arrangement is need in the case of simple models

where prototype materials are used.

2.7.4 Seismic Behavior of a Three-Story Half Scale Confined Masonry Structure (Bartolome, A.S., et al., 1992)

A three story confined masonry building modeled at 1:2.5 scale has been tested on shake

table. The vibration properties, strength of materials and axial stress of the model were kept

similar to those of the actual buildings. May 31, 1970 earthquake record was used for the

dynamic test. Each dynamic test run was preceded by free vibration test, consisting of four

pulses of small amplitude.

Flexural crack at the wall base was first developed at 0.52g. It resulted in the vertical

reinforcement to yield. At ultimate test run (0.85g) shear failure in both first story walls

occurred. The horizontal reinforcement ruptured during the last test, showing that it

effectively worked under dynamic conditions. The time period and coefficient of damping

obtained by free vibration were smaller than the pulse test and the analytically obtained

values. Both time period and damping increased with the increased in intensity of excitation.

Damping was 4% at 0.52g and increased to 7% at the final test run when PGA was 0.85g.

Stiffness of the walls decreased in the subsequent test run.

It was concluded that shear failure could occur during strong excitation even the structure

was predicted to be failed in flexure. Therefore, the design process of a confined masonry

building should include the possibility of a shear type of failure to avoid structural collapse.

37

2.7.5 Seismic Response Pattern for URM Buildings (Abram 2000)

Two reduced scale, unreinforced masonry buildings (URM) were tested on shake table in

Newmark Laboratory, University of Illinois at Urbana Champaign, USA to highlight selected

aspects of dynamic response that help confirm or deny present engineering practices for

seismic evaluation of URM buildings. The models were constructed of clay masonry units on

three-eights scale. Type O mortar was used in a two-wythe, running bond pattern. For the

first test structure perforations in each of the two parallel shear walls were chosen so that

lateral stiffness and strength of the two wall elements were similar. For the second test, the

size and placement of perforations were varied to result in dissimilar stiffness and strengths

for two walls.

Each test structure was subjected to scaled motions measured during the 1985 Nahanni

earthquake. The time scale of the recorded earthquake motion was compressed by a factor of

1.6, which was equal to the square root of the length scale of 2.5.

It is concluded that substantial nonlinear behavior, which was largely attributed to rocking

behavior of the first-story piers was observed. The models remain stable at first story drift as

large as 0.9%. Waveforms of base shear were in phase with deflection histories suggesting a

predominant first mode response. The elastic base shear, determined from measured base

motions and measured mode shapes, was as much as 4.3 times the measured base shear

maxima and as much as 7.7 times the estimated story shear rocking capacity. Measured

lateral drifts were significantly less than anticipated elastic displacements.

2.7.6 Experimental Study on Earthquake Resistant Design of Confined Masonry Structures (Ishibashi, K., et al., 1992)

This paper presents results obtained from testing of three full scale confined masonry

specimens. Each model consisted of two wall units made with clay bricks. The first

specimen, practically lacked the flexural coupling, walls were only connected through high

strength Dywidag bars that transferred the lateral force between the walls. In the second and

third specimens, walls were linked by a cast in place reinforced concrete tie beams and slab.

Parapet wall is also provided in the third specimen. Figure 2.16 illustrates the three wall

specimens and reinforcement scheme in the confining elements. The specimens were tested

38

first applying load cycles with maximum shears equal to 5 ton, 10 ton and 18 ton which

caused first crack in the masonry panel. Then displacement cycles were applied up to 0.012

drift. The specimens were designed and constructed following the requirements of the

Mexico City Building Code.

Figure 2.16 Cyclic load test specimens and reinforcement details

It has been concluded on the basis of previous research and on this research program that

masonry strength depends on the strength of brick units, and is less depended on the mortar

characteristics. The vertical load increases the shear capacity and stiffness. However, large

vertical forces reduce the available ductility of the structures. The masonry wall confinement

improves the energy dissipation characteristics and deformation capacity. The form of the

opening clearly affected the final crack pattern. However, the mode of failure for all

specimens was governed by shear deformations in the masonry panels. The type of opening

affected the initial stiffness of the specimens, the stiffness decay was similar and follow a

parabolic curve.

39

2.7.7 Cyclic Loading Tests of Confined Masonry Wall Elements for Structural Design Development of Apartment Houses in the Third World (Hiroto Kato et al 1992)

A static cyclic test on half scale confined masonry walls of three-four story apartment house,

were carried out. However, effects of axial and shear reinforcement on the load carrying

capacity, drift ratio and damage pattern were studied in this paper, the overall objectives of

the research project were to analyze damage patterns of masonry structures, to examine

improvement methods for minimizing earthquake damage, and to prepare guidelines for

confined masonry. Several static cyclic loading and shaking table tests were planned to

clarify basic characteristics of confined masonry structure.

Four confined masonry walls were constructed with different axial and shear ratio. Specimen

A with rich axial and shear reinforcement, specimen B with rich axial and poor shear

reinforcement, specimen C with poor axial and rich shear reinforcement and specimen D is

of poor axial and shear reinforcement.

It was concluded that axial reinforcement in column can improve load carrying capacity of

the confined masonry walls. The ductility of walls can be improved with the increase in shear

reinforcement as it effectively bind the unreinforced walls and avoid brittle failure. The

subjects in seismic design are to find better combinations of the ratio of axial reinforcement

and that of shear reinforcement.

40

CHAPTER 3 EXPERIMENTAL PROGRAM: MASONRY MATERIALS AND

MASONRY ASSEMBLAGE

3.1 INTRODUCTION

In order to evaluate the behavior of reduced scale typical buildings under seismic demand,

simulation of masonry materials and assemblage is essential. Extensive experimental work

has been carried out in this study for the simulation of masonry materials and masonry

assemblage. Basically, the experimental work of this study has been divided into three

phases. In the first phase mechanical properties of prototype masonry materials and

assemblages have been determined. In the second phase, simulation study has been done for

masonry materials and assemblages. The model masonry assemblages have been tested in

compression, diagonal compression and constant vertical compression and lateral cycle load.

And in the last phase of experimental study, reduced scale models have been fabricated and

tested on unidirectional earthquake simulator (shake table). The first two phases are the part

of this chapter, while the third phase has been discussed in Chapter 4 and 5. This chapter is

organized into three main sections.

Section 3.2. In this section the mechanical properties of prototype masonry materials and

masonry assemblage have been discussed. The following tests were carried out on the

masonry units and assemblage.

Masonry Unit:

I. Compressive strength II. Water absorption and density

Masonry Assemblage:

I. Compressive strength test and Modulus of Elasticity II. Diagonal Tensile (shear) Strength Test and Modulus of Rigidity

III. Cyclic Test

Section 3.3. The mechanical properties of model masonry materials and masonry assemblage

are presented in this section as follows:

41

Model Masonry Unit:

I. Compressive Strength and Density

Model Masonry Assemblage:

I. Compressive Strength and Modulus of Elasticity, II. Diagonal Tensile (shear) Strength Test and Modulus of Rigidity

III. Cyclic Test

Section 3.4. In the third and last section of this chapter, the mechanical properties of

prototype and model are compared and discussed. The actual scale factor from this study is

also compared with the true scale factor as per complete model similitude requirements.

3.2 PROTOTYPE MASONRY TEST

3.2.1 Masonry Unit (Solid Burnt Clay Brick)

Masonry unit samples were randomly collected from the local brick kiln. As described above

compressive strength and water absorption tests have been conducted on the masonry unit.

Although water absorption is not required for simulation purposes, the test has been carried

out generally to determine the physical properties of locally available brick.

3.2.1.1 Compressive Strength of Unit

Compressive strength of brick masonry units (figure 3.1) were carried out in the 200 tonne

Universal Testing Machine (UTM-200) in accordance with ASTM C 67. According to the

standard, length of test specimen for compressive strength should be equal to one half the full

length of the unit ± 1 inch. However, in this study compressive strength of full unit was

determined. Load was applied perpendicular to the bed face (length x width). The brick was

capped on both sides with gypsum 24 hours prior to testing. The compressive strength of

masonry unit is given in Table 3.1

42

Figure 3.1 Compressive strength test of solid brick masonry unit

Table 3.1 Compressive strength of masonry unit (solid burnt clay brick)

S. No Length

in (mm)

Width

in (mm)

Height

in (mm)

Crushing

Load (t)

Compressive Strength

psi (MPa)

1 8.5 (216)

4.19 (106)

2.75 (70) 27.90 1728.0

(11.9)

2 8.5 (216)

4.25 (108)

2.85 (72) 31.10 1897.4

(13.1)

3 8.63 (219)

4.25 (108)

2.9 (74) 46.10 2771.8

(19.1)

4 8.44 (214)

4.13 (105)

2.9 (74) 42.20 2672.3

(18.4)

5 8.5 (216)

4.13 (105)

2.7 (69) 39.90 2508.0

(17.3)

6 8.5 (216)

4.19 (106)

2.75 (70) 46.0 2848.0

(19.6)

7 8.44 (214)

4.25 (108)

2.75 (70) 53.80 3307.0

(22.8)

8 8.69 (221)

4.25 (108)

2.75 (70) 25.00 1492.0

(10.3)

9 8.56 (218)

4.2 (107)

2.8 (71) 39.40 2415.0

(16.7)

10 8.5 (216)

4.15 (105)

2.75 (70) 27.90 1743.0

(12.0)

Average 8.53 (216)

4.2 (107)

2.79 (71) 37.93 2338.0

(16.0) Cov (%) 1% 1% 3% 25% 25%

According to Eurocode-8 (EC 8), the minimum acceptable normalized compressive strength

of a masonry unit, normal to the bed face, is 725 psi (5.0 MPa). However, according to

43

recently developed seismic Building Code of Pakistan (SBC-07), the minimum compressive

strength of solid burnt brick is 1196 psi (8.25 MPa). Test data of masonry unit presented in

section 2.2.1.1 and test conducted in this research work reveals that the compressive strength

of unit complies with the EC 8 and PBC 07.

3.2.1.2 Water Absorption

Water absorption was determined for the masonry units in accordance with ASTM C 67. The

test data is given in Table 3.2.

Table 3.2 Water absorption of burnt clay brick

S.No Dry Wt

lb (N)

Sat. Wt

lb (N) Absorption (%)

1 5.76 (25.6)

7.02 (31.2) 21.88

2 6.15 (27.4)

7.2 (33.4) 17.07

3 5.82 (26.0)

7.02 (31.2) 20.62

4 6.09 (27.1)

7.27 (32.3) 19.38

5 6.21 (27.6)

7.31 (32.5) 17.71

Average 6.1 (27.1)

7.16 (32.0) 19.33

Cov 10%

The absorption of the masonry unit is very important property. Brick masonry made with

highly absorptive unit would have much less shear and tensile bond strength than those of

masonry made with less absorptive brick units [Calvi, G. M., et al, 1996]. In fact, brick

absorb water from mortar, leaving small amounts of water for hydration of cement which in

turn makes the mortar weak in both tension and compression and consequently resulted in

weakening of the masonry.

Although absorption of masonry unit is not considered for simulation, however, it was

determined for prototype unit to know the general trend of locally available units.

3.2.2 Masonry Mortar

Cement-Sand-Khaka (stone dust) mortar is selected for this study. The constituent materials

were mixed in proportion of one part cement to four parts each khaka and sand by volume.

44

Water to cement ratio was kept 1.6. Sand from Nizampur and khaka from Peshawar region

were used. The proportion of mortar selected is representative of field conditions. Specimens

of mortar were cured for 7 days in water and then were kept in moist room until testing day.

The 28 days compressive strength of the mortar, given in table 3.3, is determined on 2" cube.

The mortar specimens were sampled and tested according to ASTM C 109.

Table 3.3 Compressive strength of masonry mortar

S.No Area

in2 (mm2)

Load

(t)

Compressive Strength

psi (MPa)

1 4 (2581) 1.73 953.2

(6.6)

2 4 (2581) 2.11 1162.6

(8.0)

3 4 (2581) 1.55 854.0

(5.9)

4 4 (2581) 1.70 936.7

(6.5)

5 4 (2581) 1.85 1019.3

(7.0)

6 4 (2581) 1.92 1057.9

(7.3)

Average 4

(2581) 1.81 997.3 (6.9)

Cov 11%

The mean compressive strength of mortar collected from field (section 2.2.2) and used in this

study is well above the minimum compressive strength required by EC 8 and PBC 07.

According to EC 8, the masonry mortar used for un-reinforced and confined masonry should

not be less than 725 psi (5.0 MPa). And according to PBC 07 minimum compressive strength

of mortar in seismic zone 2, 3 and 4 should be 595 psi (4.1 MPa) and not greater than 75 %

of the compressive strength of masonry unit.

3.2.3 Prototype Masonry Assemblage

The mechanical properties of the constituent materials of masonry have been reported in the

preceding section. The prototype masonry has been tested for compression, diagonal tension

and cyclic behavior. The mechanical properties from these tests are to be used for simulation

purposes. The scope of the test is discussed in the subsequent sections.

45

Same type of mortar has been used for all prototype specimens. The proportion of the mortar

has been finalized to represent the field condition. One part of cement with four part each of

Khaka (stone dust) and sand have been mixed keeping water to cement ratio of 1.6. Sizes of

specimens are different for compression, tension and cyclic test.

3.2.3.1 Compression Strength and Modulus of Elasticity

The compressive strength and modulus of elasticity are the important parameters in the axial

and seismic resistance of masonry. These mechanical properties have been determined by

testing 15¾ x 9 x 19 inch (400 x 229 x 480 mm) thickness x width x height brick prism

under uni-axial compression. The mortar joint is 3/8 to ½ inch (10-12 mm) in thickness. The

bricks are laid in running bond. The prisms have been constructed by expert local mason.

The wetting of bricks and mixing of materials for mortar have been done by the mason and a

helper in such a way so as to be representative of field conditions. Samples of mortar have

been taken for the quality control.

The masonry specimens were stored and cured in the lab. The curing was started after 48

hours of specimens preparation. The specimens were wet cured for minimum of 7 days and

kept in the moist room for the rest of the time before testing.

The specimens were capped with gypsum on both ends 24 hours prior to testing. The

specimens were tested in 200 tonne Universal Testing Machine (UTM) in the Material

Testing laboratory, N-W.F.P UET, Peshawar as shown in figure 3.2. 3/4" (19 mm) thick steel

plate was used at the top between upper platen of UTM and the specimen.

Separate load cell was used for load readings. The load cell and four displacement gages

were connected with the UCAM-70 Data logger, data acquisition system. Two of the four

gages were connected on the top of the specimen to get the overall displacement of the

specimen and two (one on each face) were connected on the mid height. The dimensions and

instrumentations are shown in figure 3.3.

The compression load was applied at an average rate of 0.4 tone/sec.

46

Figure 3.2 Compression test of prototype masonry

Figure 3.3 Dimensions and instrumentations of prototype specimen for compression test.

The compressive strength of masonry prism is calculated by dividing maximum load over the

plan area of the prism. ASTM C1314 standard requires multiplying the masonry prism

strength by correction factor. The compressive strength values in the table below are un-

corrected values. The modulus of elasticity has been determined as specified in the ASTM

C1314, that is, secant modulus of elasticity between 1/20th and 1/3rd of the maximum

compressive stress of the prism.

47

Table 3.4 gives compressive strength and modulus of elasticity of brick masonry prism and

figure 3.4 illustrates the typical stress strain curve.

Table 3.4 Compressive strength and modulus of elasticity of prototype brick masonry

S.No

Designation

Compression Strength

psi (MPa)

Modulus of Elasticity "E"

ksi (GPa)

Maximum Average COV

(%) E Avg. E COV (%)

1 CE-1 705.4 (4.8)

839.63 (5.8) 24%

211.9 (1.46)

288.0 (2.0) 23%

2 CE-2 980.9 (6.7)

340.0 (2.3)

3 CE 3 1043.5 (7.2)

312.0 (2.2)

4 CE-4 628.7 (4.3)

218.0 (1.5)

The compressive strength of masonry from the equation proposed by Miha Tomazevic (Miha

Tomazevic 1999) is as follows:

0.65 0.25 ( )k b mf Kf f MPa= (3.1)

= 5.39 MPa or 781 psi

Where:

fb = Normalized compressive strength of unit in MPa

fm = Compressive strength of mortar in MPa

k is a constant and its value depends on the classification of masonry unit. In this case k is

0.5. By comparing compressive strength from experiment and equation, good correlation is

obtained. However, the equation is an approximate approach and could not be preferred over

experimentally determined value. The value of E is 342 times the compressive strength of

masonry, which lies between the range specified in (Miha Tomazevic 99).

48

y = 2E+09x3 - 5E+07x2 + 389478xR2 = 0.9942

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

1000.0

1100.0

0 0.002 0.004 0.006 0.008 0.01 0.012

Strain (in/in)

Stre

ss (p

si)

Figure 3.4 Typical stress strain curve of prototype brick masonry in compression

3.2.3.2 Diagonal Tension (Shear) in Masonry

In order to determine the tensile strength (shear strength) of masonry five square specimens

of nominal size 28¾ x 28¾ x 9 inch (730 x 730 x 229 mm) have been prepared and tested in

accordance with ASTM C519-02. Although, ASTM standards specify 48 x 48 inch

specimen, smaller specimen have been constructed to better handle them. The specimens

were constructed in English bond with joints thickness of 3/8 to ½ inch (10-12 mm). Figure

3.5 shows the diagonal specimen during testing.

The dimensions and instrumentations are illustrated in figure 3.6. Four gages have been used

to measure vertical shortening and horizontal extensions. Two gages are connected in a way

to measure vertical shortening and the other two horizontal extensions. The specimen is

positioned in standard loading shoes on the top and bottom corners. Vertical compression

load is applied through 50 tonne actuator in a manner that the specimen failed in 3-4 minutes.

The load and displacement readings of a specimen (PTG-5) could not be recorded because of

data logger not in a recording mode.

49

Figure 3.5 Diagonal compression (shear) test

Figure 3.6 Dimensions and instrumentations of diagonal tension test

The shear strength is calculated by the following formula:

0.707sPSA

= (3.2)

Where:

P = applied load, lb,

A = net area = (W+H)t/2

W = width of specimen, inch,

50

H = height of specimen, inch,

t = thickness of specimen, inch

The shear strain is calculated as follows:

( )V Hg

γ∆ + ∆

= (3.3)

where:

γ = shear strain,

∆V = vertical shortening, inch,

∆H = horizontal extension, inch.

The modulus of rigidity, G is calculated as follows:

sSGγ

= (3.4)

as ASTM E519 does not specify any range of stresses for the determination of modulus of

rigidity. However, 1/20th and 1/3rd of the maximum shear stresses are taken over which

stresses are assumed linear. The shear strength and modulus of rigidity is given in table 3.5.

Table 3.5 Tensile strength and modulus of rigidity of prototype brick masonry

S.No Designation

Shear Strength

psi (MPa)

Modulus of Rigidity "G"

ksi (GPa)

Maximum Average Cov (%) G Average Cov

(%)

1 PTG-1 41.7 (0.29)

51.3 (0.35) 14%

30.6 (0.21)

28.1 (0.20) 37%

2 PTG-2 49.7 (0.34)

15.6 (0.11)

3 PTG-3 55.9 (0.39)

26.0 (0.18)

4 PTG-4 57.8 (0.40)

40.4 (0.28)

The shear strength is about 6% of the compressive strength. Shear modulus is 10% of the

elastic modulus which lies in the experimentally evaluated range of 6% to 25% suggested by

Tomazevic M., 1999. According to EC 6 specification the shear modulus, G is 40% of the

elastic modulus is much higher then the experimental results.

51

3.2.3.3 Cyclic Test of Prototype Masonry Walls

Five 36 inch square specimens were prepared in English bond for cyclic test. The mortar

joint was ¾ to ½ inch (10-12 mm) thick. Reinforced concrete beams, 9" in thickness, were

provided at the top and bottom of the masonry wall. The specimens were wet cured for 7-10

days and was kept in moist room until testing. Mortar samples were collected during

construction of the masonry specimens for quality control. The mortar samples were tested at

the same day of cyclic test. The specimens were white washed two days prior to testing for

the visibility of cracks during testing.

The dimensions and instrumentations are illustrated in figure 3.7. The specimens were tested

in straining frame, structural laboratory. Three load cells were used for applying vertical

compression and horizontal cyclic loads. A 50 tonne capacity actuator was used for applying

constant vertical compression load. Vertical load was applied on 3" (76 mm) thick steel plate

placed on 1.5" (38 mm) diameter steel rollers. The steel rollers in turn are rolling on a highly

polished 3/8" (10 mm) thick steel plate during the horizontal displacement of the specimen.

Two 25 tonne capacity actuators were used to apply horizontal cyclic load, each one applying

half cycle. Two LVDTs were connected on either side of the specimen to measure top

displacement. Two LVDTS were also connected at the bottom of the specimen to measure

shear sliding if any. A LVDT is also used to measure the slippage of the bottom concrete

beam over the steel girder (figure 3.8).

The bottom beam of the specimen is connected with a stiff steel girder with the help of four

bolts on each side.

All the instruments are connected with UCAM70 data logger for data acquisition. A list of

equipment and their specification is given in Appendix A.

52

Figure 3.7 Dimensions and instrumentations of prototype cyclic load test

Figure 3.8 Cyclic test setup

7 tonne of vertical compression load was applied on the specimen. The vertical compression

load is equivalent to 47 psi (0.32 MPa) compression stresses which is representing vertical

stresses in the pier in two story typical Pakistani masonry building (5 marlas/1361 sft typical

houses). The test was displacement control. Displacement history is illustrated in figure 3.9.

53

-14.0-12.0-10.0-8.0-6.0-4.0-2.00.02.04.06.08.0

10.012.014.0

Dis

plac

emen

t (m

m)

Figure 3.9 Displacement history for prototype cyclic test.

Figure 3.10 shows typical hysteresis loop of the cyclic test. The load-displacement envelop

(figure 3.11) was plotted by maximum load and its corresponding displacement in the first

cycle of each increment. Rocking was predominant failure mode of all specimens. One

specimen was damaged during transportation and positioning. Bilinear idealized curve is also

plotted as shown in figure 3.11.

54

Figure 3.10 Typical load-displacement hysteresis loop

Load-Displacement Curve

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

Horizontal Displacement (mm)

Hor

izon

tal L

oad,

Ton

e

Figure 3.11 Hysteresis envelop and bilinear idealized curve

Load-Displacement Hysteresis loop

-6

-4

-2

0

2

4

6

-14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

Displacement (mm)

Hor

izon

tal L

oad

(t)

_____ Hystersis Envelope

------- Idealized Curve

55

The main parameters of seismic resistance, such as the tensile strength, ft, effective stiffness,

Ke, shear modulus G and ductility factor µ are presented in the table 3.6.

Table 3.6 Dimensions and mechanical properties of prototype masonry

Designation

h

in (mm)

l

in (mm)

t

in (mm)

E

Ksi

(GPa)

σ

psi

(MPa)

Hmax

Kips

(kN)

ft

psi

(MPa)

Ke

kips/in

(kN/mm)

G

psi

(MPa)

µ

(%)

G/E

ratio

PC-1

39.7

(1008)

36.0

(915)

8.5

(217)

290

(2)

35.8

(0.25)

0.96

(42.66)

32.2

(0.22)

82.39

(14.48)

13.4

(92.41) 3.64 5

PC-2

39.8

(1010)

36.8

(935)

8.6

(220)

290

(2)

47.0

(0.32)

1.07

(47.56)

33.3

(0.23)

100.01

(17.58)

16.75

(115.5) 4.30 6

PC-3

40.2

(1021)

37.8

(961)

8.7

(220)

290

(2)

47.0

(0.32)

1.06

(47.28)

30.5

(0.21)

93.34

(16.41)

14.41

(99.41) 3.84 5

PC-4

40.2

(1021)

37.8

(961)

8.7

(220)

290

(2)

47.0

(0.32)

1.1

(49.05)

32.1

(0.22)

112.43

(19.76)

17.53

(120.9) 6.04 6

PC-5

39.4

(1001)

36.4

(925)

8.7

(221)

290

(2)

48.7

(0.34)

1.2

(54.88)

39.0

(0.27)

45.02

(7.91)

6.9

(47.59) 2.28 2

Average

40.0

(1015)

37.1

(943)

8.6

(219)

290

(2)

44.2

(0.3)

1.0

(46.64)

32.0

(0.22)

97.04

(17.1)

15.52

(107.1) 4.02 5

Specimen PC-5 developed pre-testing horizontal crack during transportation and probably

this is reason for its low effective stiffness, Ke and modulus of rigidity, G as compared to

other specimens. The tensile strength (ft) is determined by using Turnsek equation (Turnsek

and Cacovic, 1971) as given below:

( )σ στ⎛ ⎞= + −⎜ ⎟⎝ ⎠

221.5

2 2ft (3.5)

Where:

σ = Average compressive strength in the horizontal cross-section of the wall

= vertical compression load divided by plan area (that is length x thickness) of the

wall.

τ = Maximum shear stress in the horizontal plan area of the wall

= Maximum horizontal load (Hmax) divided by plan area (Aw)

56

Modulus of rigidity, G in the table is calculated by the following formula:

=−

⎛ ⎞⎜ ⎟⎝ ⎠

21.21.2

KeG Aw Keh hh

l

(3.6)

Where:

Ke = Effective Stiffness,

Aw = Area of wall (length x thickness),

h = Height of the wall,

l = Thickness of the wall

In order to compare tensile strength from diagonal compression test and cyclic test, good

correlation is obtained. Modulus of rigidity, G obtained from the cyclic test is smaller than

those evaluated from diagonal compression test.

3.2.3.4 Target value of Prototype Materials

As discussed previously, the scale factor of 4 and complete model similitude requirements

have been selected based on simulator capacity. According to the similitude laws, the strain

and density of model should be kept same as that of the prototype materials, however, stress

should be scaled with scale factor. The prototype materials used are the actual field

representation.

The target values of prototype materials is given in Table 3.7

57

Table 3.7 Target mechanical values of materials

Description Prototype Model (Target Value) Prot/Model

Compressive Strength of Masonry unit, psi (MPa) 2338.0 (16.12)

585 (4.03) 4

Density of Masonry unit, Ib/ft3 (kN/m3) 101.0 (15.87)

101.0 (15.87) 1

Compressive Strength of Masonry Mortar, psi (MPa) 997.3 (6.88)

249 (1.72) 4

Compressive Strength of Masonry,ƒk, psi (MPa) 839.6 (5.79)

210 (1.45) 4

Tensile Strength (shear) of Masonry,ƒtk, psi (MPa) 51.27 (0.35)

13 (0.09) 4

Modulus of Elasticity of Masonry, E, ksi (GPa) 288.0 (1986.2)

72.0 (0.49) 4

Shear Modulus of Masonry, G, ksi (GPa) 28.11 (0.19)

7.03 (0.05) 4

Compressive Strength of Concrete, psi (MPa) 1500 (10.34)

375 (2.57) 4

Yield Stress of Reinforcing Steel, psi (MPa) 94,500.0 (652.0)

23,625.0 (163.0) 4

3.3 MODEL MASONRY

A series of trial mixes have been prepared for the simulating target mechanical and physical

properties of masonry materials. A number of model walls have also been constructed and

tested for subsequent analysis and extrapolation of the test results to prototype buildings.

3.3.1 Model Masonry Unit

Model masonry units have been fabricated from special mortar containing cement, lime and

surkhi. Surkhi is burnt clay brick remains. Surkhi is used instead of sand for its light weight

in the mortar mixture to fulfill the density requirement. For sand mortar the density was more

than the required. The use of Surkhi ensured that the density of model was practically same

as that of the prototype. The gradation of surkhi is illustrated in figure 3.12. Several mixes

have been tried before the final selection was made based on density and compressive

strength.

The mix proportion selected is 1:1:5. The mix is poured in the mould (figure 3.13) and

compacted in two layers. The compacted bricks are then removed from the mould by

pressing the mould against wooden blocks. The mix proportion is designed as to be easily

58

compacted and de-molded with out damaging shape of masonry unit and fulfilling the

similitude requirement. Ordinary Portland cement has been used for the mix. Surkhi from

local brick kiln near Peshawar city has been used.

Three different sizes of model bricks (figure 3.14) were fabricated. One with size 2.2 x 1.1 x

0.67 (56 x 27 x 17 mm), is the actual reduced size of the prototype bricks and is designated

as brick #1. The second with size 2.2 x 1.1 x 1.3 (56 x 27 x 34 mm), is double in height and

the third double in width that is 2.2 x 2.2 x 0.67 (56 x 56 x 17 mm) is fabricated to reduce the

number of masonry bricks required and reduce the fabrication efforts of the model building.

Model bricks double in width are designated as brick #2 and double in height as brick #3.

The density and compressive strength of the model masonry unit at 28 days is given in table

3.8. The density and compressive strength is mean value of 10 model bricks. The

compressive strength of model brick, double in width could not be determined because of its

aspect ratio. The specific mass has been obtained by weighing the brick units and measuring

the actual dimensions.

0

20

40

60

80

100

4 8 16 30 50 100

Sieve Number

Perc

ent p

assi

ng (%

)

Figure 3.12 Composition of Surkhi

59

Figure 3.13 Mould for model masonry unit (size 56 x 27 x 17 mm)

Figure 3.14 Three different types of model masonry

Table 3.8 Compressive strength and density of model masonry units

Model Masonry Unit Compressive

Strength

psi (MPa)

Cov

(%)

Density

lb/ft3 (kN/m3)

Cov

(%)

Brick #1 (56 x 27 x 17 mm)

634.79 (4.4) 7 98.10

(15.42) 1

Brick #2 (56 x 27 x 34 mm)

500.34 (3.45) 9 100.52

(15.80) 3

3.3.2 Model Masonry Mortar

Different cement and lime based mixes have been prepared for the model masonry mortar.

Indigenous materials, for example, Khaka, marble powder and surkhi are used in the mortar

60

mixes for their effects on the compressive strength and flow value. The proportions of the

mixes have been arbitrarily selected. Following are the different combination of materials:

A. Cement-Lime Based Mortar

1. Cement : Lime : Sand (CLS)

2. Cement : Lime : Khaka (CLK)

3. Cement : Lime : Marble Powder (CLP)

4. Cement : Lime : Sand : Marble Powder (CLSP)

5. Cement : Lime : Surkhi (CLSr)

6. Cement : Lime : Sand : Surkhi (CLSSr)

B. Lime Based Mortar

1. Lime : Sand : Surkhi (LSSr)

2. Lime : Sand : M. Powder (LSP)

Ordinary Portland cement and hydrated lime is used for the mixes. Sand used is the clean

river sand having size from 0-1 mm. The gradation of sand is shown in figure 3.15.

Table 3.9 and table 3.10 gives the compressive strength and flow value for the cement based

and lime based mortar mixes, respectively. Three 2" (51 mm) cube are used to determine the

compressive strength of mortar.

0

20

40

60

80

100

4 8 16 30 50 100

Sieve Number

Perc

ent p

assi

ng (%

)

Figure 3.15 Composition of Sand

61

Table 3.9 Compressive strength of cement based-masonry mortar

No Specimen

Designation

Mix

proportion

Water

content*

(ml)


7 days 28 days 90 days

Avg. Strength Avg.

Strength

Cov

(%)

Avg.

Strength

1 CLS 0411 0.4:1:11 250 15.61 (0.11) 27.55 (0.19) 9.4 -

2 CLS 1111 1:01:11 300 110 (0.76) 135.91 (0.94) 6.2 -

3 CLS 1111/F 1:01:11 300 104.69 (0.72) 120 (0.83) 8.2 -

4 CLS 0.4111/F 0.4:1:11 300 33.37 (0.23) 42.24 (0.29) 19.9 -

5 CLS 0418/F 0.4:1:8 450 87.06 (0.6) 110.2 (0.76) 5 -

6 CLS 1111/F 1:01:11 375 111.72 (0.77) 141.42 (0.98) 18 -

7 CLS 4111/F 0.4:1:11 375 56.59 (0.39) 71.63 (0.49) 7.7 -

8 CLS 1210/F 1:02:10 400 107.37 (0.74) 135.91 (0.94) 19.2 211.22 (1.46)

9 CLS 0.528/F 0.5:2:8 425 85.61 (0.59) 108.36 (0.75) 10.6 163.46 (1.13)

10 CLK 0528/F 0.5:2:8 550 120.43 (0.83) 152.44 (1.05) 4.2 163.46 (1.13)

11 CLSK05132/F 0.5:1:3:2 375 171.21 (1.18) 216.73 (1.49) 8.2 277.34 (1.91)

12 CLS0418 0.4:1:8 400 58.04 (0.4) 73.47 (0.51) 17.3 108.36 (0.75)

13 CLS125 1:02:05 475 200.23 (1.38) 253.46 (1.75) 4.3 277.34 (1.91)

14 CLS115 1:01:05 450 188.63 (1.3) 238.77 (1.65) 21.3 290.19 (2)

15 CLP1212 1:02:12 500 113.18 (0.78) 143.26 (0.99) 3.8 159.79 (1.1)

16 CLP1220 1:02:20 500 79.8 (0.55) 101.02 (0.7) 6.3 102.85 (0.71)

17 CLP1110 11:10:00 475 107.37 (0.74) 135.91 (0.94) 13 128.57 (0.89)

18 CLP126 1:02:06 575 140.74 (0.97) 178.16 (1.23) 1.8 213.05 (1.47)

19 CLP146 1:04:06 650 82.71 (0.57) 104.69 (0.72) 5.3 150.61 (1.04)

20 CLP1412 1:04:12 600 88.51 (0.61) 112.04 (0.77) 10.2 143.26 (0.99)

21 CLSP1233 1:2:3:3 500 163.96 (1.13) 207.54 (1.43) 7.7 209.38 (1.44)

22 CLSP1466 1:4:6:6 550 53.69 (0.37) 67.96 (0.47) 9.4 108.36 (0.75)

23 CLSP1433 1:4:3:3 600 105.92 (0.73) 134.08 (0.92) 11.9 104.69 (0.72)

24 CLSr1212 1:02:12 750 294.55 (2.03) 372.84 (2.57) 6.8 299.38 (2.06)

25 CLSr1220 1:02:20 750 210.39 (1.45) 266.32 (1.84) 3.2 134.08 (0.92)

26 CLSr1110 1:01:10 800 156.7 (1.08) 198.36 (1.37) 10 113.87 (0.79)

27 CLSSr1466 1:4:6:6 700 146.55 (1.01) 185.5 (1.28) 18.1 0 (0)

28 CLSSr1233 1:02:03:3 650 0 (0) 0 (0) - 214.89 (1.48)

29 CLSSr1133 1:03:03 650 194.43 (1.34) 246.11 (1.7) 3.4 185.5 (1.28)

62

Table 3.10 Compressive strength of lime based-masonry mortar

No Speciman

Designation

Mix

proportion

Water

content*

(ml)


7 days

Strength 28 days Strength

90 days

Strength

Avg.

Strength

Avg.

Strength

Cov

(%) Avg. Strength

1 LS 13/F 1:03:00 450 59.5 (0.41)

75.3 (0.52) 11.2 134.0

(0.92)

2 LSP133 1:03:03 450 94.3 (0.65)

119.4 (0.82) 25.4 113.9

(0.79)

3 LSSr133 1:03:03 650 108.8 (0.75)

137.75 (0.95) 8.0 126.7

(0.87)

4 LSSr11515 1:1.5:1.5 650 94.3 (0.65)

119.4 (0.82) 21.8 132.2

(0.91) *The water content is required for 3.90 lb (1765 g) of dry materials mixed in the proportion given in column 3 Cement lime sand mortar (CLS115) has been selected for its 28 days compressive strength

matching prototype mortar strength.

3.3.3 Micro Concrete

For the slab and confining elements concrete, different cement-sand and cement-lime-sand

mixes have been prepared. Ordinary Portland cement and hydrated lime has been used. River

sand of grain size from 0-2 mm have been used for the micro concrete. 7-days and 28-days

compressive strength data of micro concrete is presented in table 3.11.

Cement sand mortar (CS16) has been selected for floor concrete and cement-lime-sand

(CLS115) has been used for confining element. The selected mix proportion represents the

lower bound value of compressive strength of concrete as discussed in section 2.2.

63

Table 3.11 Compressive strength of micro-concrete

S.No Designation Water

content (ml)

7 days Compressive

Strength, psi (MPa)

28 days Compressive Strength

psi (MPa)

Average Cov (%) Average Cov (%)

1 CS15 550 ml 391.7 (2.7) 3.14 870.0 (6) 8.98

2 CS16 - 287.6 (1.98) 6.45 388.2 (2.68) -

3 CS110 550 ml 79.5 (0.55) 18.36 185.9 (1.28) 13.34

4 CLS114 650 ml 575.3 (3.97) 6.45 1117.8 (7.71) 14.0

5 CLS115 - 212.8 (1.47) 7.61 367.2 (2.53) -

6 CLS116 650 ml 219.8 (1.52) 15.2 322.7 (2.23) 26.45

7 CLS1110 600 ml 142.6 (0.98) 8.63 386.0 (2.66) 3.63

8 CLS1112 550 ml 123.9 (0.85) 16.58 266.6 (1.84) 27.35

9 CLS128 700 ml 108.7 (0.75) 14.7 161.4 (1.11) 8.69

10 CLS1210 600 ml 114.6 (0.79) 4.67 261.9 (1.81) 15.46

11 CLS1212 600 ml 98.2 (0.68) 15.56 173.0 (1.19) 45.87

12 CLS1215 550 ml 74.8 (0.52) 10.82 184.7 (1.27) 8.77

13 CLS148 900 ml 72.5 (0.5) 14.78 81.8 (0.56) 44.0

*The water content is required for 6.10 lb (2771 g) of dry materials mixed in the proportion given in column 2

3.3.4 Reinforcing Bar

3 mm diameter aluminum wire has been used as model reinforcing bar for confining

elements. The tensile strength of the wire is 29,000 psi (200 MPa). For the model concrete

floor, 3 mm diameter galvanized wire was used.

3.3.5 Model Masonry

In order to fulfill the simulation requirements, model masonry walls have been tested in

compression, diagonal tension and cyclic test. Modulus of elasticity, modulus of rigidity and

energy dissipation capacity has been determined for the extrapolation purposes.

3.3.5.1 Compressive Strength and Modulus of Elasticity

Model walls from all the three types of model bricks were constructed. The walls had the

same bond pattern as was followed for the prototype masonry walls. Horizontal and vertical

64

joint thickness was 2.5-3.0 mm. The walls have been built in CLS 115 mortar. No moist

curing has been done for the walls. Three walls have been built for each type of brick unit.

The walls have been instrumented with four deflection gages. Two gages were used to

measure vertical deformation. The other two gages were connected in the way to measure

deformation of overall depth of the wall. Both sides of the model walls were capped with

gypsum 24 hours prior to testing. The walls have been tested in the universal testing

machine. Deformation and load data has been acquired by data logger. The dimensions and

instrumentations of the walls for compression strength is illustrated in figure 3.16. The

compression strength and modulus of elasticity of the model wall is given in table 3.12.

Figure 3.17-3.19 shows typical stress strain curve for the three different types of bricks

prism.

Figure 3.16 Dimensions and instrumentations of model walls for compression.

65

Table 3.12 Compressive strength and modulus of elasticity of model masonry

S.No

Designation

Compression Strength

psi (MPa)

Modulus of

Elasticity "E", ksi (GPa)

fc Avg. fc Cov

(%) E Avg. E Cov (%)

1 CE 2.1/111-1 322.63 278.6

(1.92) 26%

50.86 46.28

(0.32) 29% 2 CE 2.1/111-2 316.97 56.68

3 CE 2.1/111-3 196.13 31.31

4 CE 2.1/211-1 701.36 692.9

(4.78) 4%

137.57 96.54

(0.66) 37% 5 CE 2.1/211-2 663.60 74.26

6 CE 2.1/211-3 713.77 77.78

7 CE 1.9/311-1 654.89 707.2

(4.88) 10%

70.62 56.15

(0.39) 22% 8 CE 1.9/311-2 677.11 48.11

9 CE 1.9/311-3 789.50 49.72

It could be seen from table 3.12 that compressive strength of larger sized bricks (that are

brick #2 and 3) are more than the actual model brick. The masonry constructed from brick #2

and 3, resulted in high elastic modulus than the masonry constructed of brick #1. In order to

compare compressive strength and modulus of elasticity of model and prototype good

correlation has been obtained.

Specimen designation is explained below:

CE 2 / 1 1 1 -1

Aspect ratio

Type of brick Masory mortar

Compression and Modulus of Elasticity

Mortar for Brick No. of specimen

66

y = 6E+07x3 - 4E+06x2 + 63813xR2 = 0.9838

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0 0.005 0.01 0.015 0.02 0.025 0.03

Strain (in/in)

Stre

ss (p

si)

Figure 3.17 Typical stress-strain curve for model brick No.1

y = 6E+07x3 - 4E+06x2 + 63813xR2 = 0.9838

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

900.0

0 0.005 0.01 0.015 0.02 0.025

Strain (in/in)

Stre

ss (p

si)


67

y = 6E+07x3 - 4E+06x2 + 63813xR2 = 0.9838

-100.0

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

0 0.005 0.01 0.015 0.02 0.025 0.03

Strain (in/in)

Stre

ss (p

si)


3.3.5.2 Tensile Strength and Modulus of Rigidity

Model masonry square walls of size 6.81 x 6.81 x 2.2 (173 x 173 x 56 mm) were constructed

and tested in diagonal compression complying ASTM C 1314. Three walls, each from the

three types of bricks, were tested at the age of 28 days. The walls were constructed in English

bond with 2.5-3 mm joint thickness (figure 3.20). The modeled walls were air cured in the

laboratory at temperature 20-25 C°.

68

Figure 3.20 Model wall for tensile (shear) strength

Four displacement transducers were used to capture horizontal elongation and vertical

shortenings. The two horizontal and two vertical transducers were connected with a steel

plate as shown in figure 3.21. Steel shoes were placed on top and bottom of the specimen.

The specimens were properly caped with gypsum. The walls dimensions are illustrated in

figure 3.22.

Figure 3.21 Model wall during diagonal compression (shear) test

69

Figure 3.22 Dimensions of Model walls

The walls were tested in 200 tonne UTM. Additional load cell, connected with the UCAM 70

data logger, were used to capture load values. The displacement gages were connected with

the data logger. Results of diagonal tension test are presented in Table 3.13. Shear stress to

shear strain is plotted in figure 3.23-3.25.

70

Table 3.13 Tensile (shear) strength and modulus of rigidity of model masonry

Specimen

Designation

Specimen Dimensions Gage length

in

(mm)

Diagonal

in

(mm)

Tensile

Strength

psi

(MPa)

Modulus of

Rigidity

ksi

(MPa)

Width

inch

(mm)

Height

inch

(mm)

Thickness

inch

(mm)

Area

in2

(mm2)

Hori Vert

TG3-111

1 6.6 (169) 7.2 (183) 2.2 (56) 15.3 (9852) 11.4 (290) 11.1 (282) 24.5 (621) 33.6 (0.23) 14.1 (0.1)

2 7.1 (180) 7.5 (189) 2.2 (55) 15.7 (10110) 11.6 (295) 11.9 (302) 25.9 (658) 35.8 (0.25) 12.4 (0.09)

3 6.6 (169) 7.1 (180) 2.1 (54) 14.5 (9323) 11.6 (295) 11.1 (282) 24.5 (622) 28.5 (0.2) 23.9 (0.17)

4 7.1 (180) 7.3 (184) 2.2 (56) 15.8 (10194) 11.7 (297) 11.7 (297) 25.5 (648) 30.0 (0.21) 15.6 (0.11)

Average 32.0 (0.22) 16.5 (0.11)

Cov 10 31

TG3-211

1 7.1 (180) 7 (177) 2.2 (56) 15.5 (9968) 15.3 (389) 15.4 (391) 24.7 (626) - -

2 6.7 (170) 6.7 (170) 2.2 (55) 14.5 (9368) 15.2 (386) 15.3 (389) 23.8 (603) 95.7 (0.66) 31.1 (0.21)

3 7.1 (180) 6.7 (171) 2.2 (56) 15.1 (9735) 15.4 (391) 15.2 (386) 24.6 (625) 109.1 (0.75) 33 (0.23)

4 6.7 (171) 6.6 (167) 2.2 (56) 14.7 (9452) 14.7 (373) 15 (381) 23.7 (601) 62.4 (0.43) 84.4 (0.58)

Average 89.1 (0.61) 49.5 (0.34)

Cov 27 61

TG3-311

1 7.2 (183) 6.5 (166) 2.3 (57) 15.5 (10006) 15.1 (384) 15.4 (391) 23.9 (607) 50.2 (0.35) 33.4 (0.23)

2 7.2 (183) 6.3 (159) 2.2 (57) 15.1 (9755) 15.1 (384) 14.8 (376) 23.6 (599) 46.0 (0.32) -

3 7.1 (181) 6.4 (161) 2.3 (57) 15.2 (9806) 15 (381) 14.8 (376) 24 (610) 64.5 (0.44) 15.2 (0.1)

4 7.4 (187) 6.3 (160) 2.2 (55) 14.7 (9484) 15 (381) 14.9 (378) 24.5 (622) 52.3 (0.36) 29.6 (0.2)

Average 53.2 (0.37) 26.1 (0.18)

Cov 15 37

The shear strength and shear rigidity of masonry constructed of brick No. 2 and No. 3 are

more than the masonry constructed of brick #1. Model constructed of brick No. 2 and No. 3

would be stiff enough to represent the prototype. The strength of model would also not

represent the prototype building. The strength and stiffness of masonry from brick No. 1 is

also more than the prototype, however, the actual model bricks could be used for fabricating

the model buildings.

71

y = 6E+07x3 - 2E+06x2 + 14860x - 5.4344R2 = 0.9846

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

0.0000 0.0020 0.0040 0.0060 0.0080 0.0100 0.0120 0.0140

Srain (in/in)

Stre

ss (p

si)


y = 7E+09x3 - 5E+07x2 + 101006x - 5.2088R2 = 0.9791

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035

Srain (in/in)

Stre

ss (p

si)


72

y = 6E+08x3 - 8E+06x2 + 34502x + 2.1649R2 = 0.9862

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0.0000 0.0010 0.0020 0.0030 0.0040 0.0050 0.0060

Srain (in/in)

Stre

ss (p

si)


3.3.5.3 Cyclic Test of Model Wall

In order to evaluate the parameters which define the seismic behavior of masonry, such as

energy dissipation and ductility capacity, model walls have been constructed in English bond

with joint thickness 2.5 to 3 mm and tested under constant vertical compression load and

cyclic displacement. The walls have been constructed on 3" (76 mm) thick plain concrete

block. A 2" (51 mm) thick plain concrete beam is provided at the top of the wall to uniformly

distribute the compression load.

The model walls have been constructed in cement-lime-sand CLS115 mortar. The walls have

been kept in moist room until testing. The walls were tested at 28 days of casting. The

specimens have been tested in test set up as shown in figure 3.26. The test was displacement

control. Horizontal displacement history (figure 3.27) has been applied through two

horizontal actuators. Vertical load was applied through vertical actuator. Displacement gages

were connected to measure horizontal top displacement.

As shown in figure 3.26 the model wall was fixed with a 12 inch (30 cm) square steel girder.

The girder itself is supported on other steel girders of the straining frame. The square steel

girder was not fixed with the supporting girders. It was assumed that the self weight of the

73

girder would balance the lateral load, however, the girder was observed to rotate during the

application of lateral displacement on the specimen from north side actuator (left side in

figure 3.26). The effect of rotation of the girder could be seen in load-displacement curve,

figure 3.28.

Figure 3.26 Model wall test setup

-4.0

-2.0

0.0

2.0

4.0

Disp

lace

men

t (m

m)

Figure 3.27 Displacement-time history for model wall cyclic test

74

Figure 3.28 Load-displacement curve

It could be seen from the load-displacement curve that more resistance has been shown in the

upper half of the cycle as compared to the lower half cycle. It could be attributed to the

lifting (rotation) of steel girder. In other words the input energy has been partly used to

overcome the weight of the girder. However, because the steel girder was placed touch with

the steel column of the straining frame, no sign of rotation was observed while applying

displacement from south actuator (right side in the figure 3.26).

The walls were observed to fail in rocking mode. A horizontal crack developed at the

interface of masonry wall and base slab/beam or at the second last mortar joint (figure 3.29).

Almost same manner of cracks have been observed in the prototype walls during cyclic

testing. Cracks were also observed in the un-reinforced base slab/beam.

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0

Displacement (mm)

Horiz

onta

l Loa

d (t)

75

Figure 3.29 Cracked model wall during cyclic test

The lateral resistance parameters evaluated during cyclic test of the model walls are given in

table 3.14. One wall has been damaged during transportation and fixing operation. It is worth

mentioning that behavior of wall to lateral displacement from the south actuator has only

been analyzed and present in the table. The rotation of the girder could not be filtered from

the upper half cycle to obtain the actual behavior of the wall. The hysteresis envelopes are

shown in figure 3.30. The idealized bilinear curve is also plotted in the same figure to

evaluate effective stiffness, Ke and ductility ratio, µ.

Table 3.14 Mechanical properties of model walls

Designation

h

inch

(mm)

l

inch

(mm)

t

inch

(mm)

E

psi

(GPa)

σ

psi

(MPa)

Hmax

kips

(kN)

ft

psi

(MPa)

Ke

kips/in

(kN/mm)

G

ksi

(MPa)

µ

(%)

G/E

Ratio (%)

MC-111-1 8.3

(210)

9.4

(238)

2.2

(56)

46.4

(0.32)

11.6

(0.08)

0.31

(1.39)

17.4

(0.12)

9.73

(1.71)

5.02

(34.59) 3.76 11%

MC-111-2 8.5

(215)

9.1

(230)

2.2

(57)

46.4

(0.32)

11.6

(0.08)

0.52

(2.31)

33.35

(0.23)

5.23

(0.92)

2.74

(18.88) 3.3 6%

Average 8.4

(213)

9.2

(234)

2.2

(56.5)

46.4

(0.32)

11.6

(0.08)

0.41

(1.85)

24.65

(0.17)

7.45

(1.31)

3.88

(26.74) 3.53 8%

Prototype 40

(1015)

37.1

(943)

8.6

(219)

290.0

(2)

43.5

(0.3)

10.45

(46.64)

31.9

(0.22)

97.05

(17.06)

15.52

(107.06) 4.45 5%

Theoretical S.F 4 4 4 4 4 64 4 16 4 1

Actual S.F 4.8 4.0 3.9 6.2 4 25.2 1.3 13 4 1.3

76

Load-Displacement Curve

-0.160

-0.140

-0.120

-0.100

-0.080

-0.060

-0.040

-0.020

0.000-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0

Horizontal Displacement (mm)

Hor

izon

tal L

oad,

Ton

e

Figure 3.30 Typical hysteresis envelope of model wall for south side loading

It could be seen from the table that full compliance with the complete model similarity

requirements has not been obtained in some of the parameters. However, stiffness Ke and

modulus of elasticity and ductility ratio are adequately modeled. The experimental set up for

the cyclic test of model walls could be attributed to the non-compliance.

3.4 COMPARISON OF MECHANICAL PROPERTIES OF PROTOTYPE AND

MODEL MASONRY ASSEMBLAGE

In this section, the physical and mechanical properties of model and prototype masonry

materials are compared. The mechanical properties of model walls are extrapolated to

prototype and compared with the actual experimentally determined mechanical properties of

prototype walls. Actual scale factor is compared with the theoretical scale factor for

compression strength, modulus of elasticity, tensile (shear) strength and modulus of rigidity

and other parameter of the cyclic load test of masonry assemblage.

77

3.4.1 Masonry Materials

As mentioned earlier, different trial mixes have been prepared for simulating compressive

strength of masonry mortar, micro concrete and masonry unit. Cement-lime-sand mortar

(CLS 115) is selected as masonry mortar for its extrapolated 28 days compressive strength

close to 28 days compressive strength of prototype mortar. The 28 days compressive strength

of model mortar was 239 psi (1.65 MPa) and its extrapolated value becomes 956 psi (6.6

MPa) as compared to 997 psi (6.9 MPa). The prototype mortar is representing the field

condition.

Although, prototype concrete has not been designed and tested in this research work,

however, decision was made to assume 1500 psi (10.35 MPa) as target value. The

compressive strength for prototype concrete represents lower bound used in the current

masonry construction practice in Peshawar and earthquake affected area. However, relatively

high compressive strength of 2175 psi/15 MPa (C15) has been recommended by researchers

(Miha Tomazevic 99) for the confining element. Cement-lime-sand (CLS 115) having

compressive strength of 367 psi (2.53 MPa) was finalized as micro-concrete for confining

elements. However, relatively high strength micro concrete (Cement-sand CS16) was

designed for floor slabs.

However, the data of masonry unit analyzed in section 2.2 is scattered; the prototype

masonry unit used in this study is considered as reference for modeled units. Different mortar

mixes for simulating compressive strength and density of masonry unit have been prepared.

The two main types of combination of constituent materials were cement-lime-sand and

cement-lime-surkhi. Density of modeled brick from cement-lime-sand mix was high when

extrapolated to prototype. Cement-lime-surkhi (CLSr 125) mix has been finalized. As

mentioned earlier, three different shapes of model bricks have been prepared. The simulation

was done on the actual model brick.

The physical and mechanical properties of model and prototype masonry materials are

compared in table 3.15. In the table, the actual and theoretical scale factor is also compared.

It could be seen that good correlation exists between true and theoretical scale factor.

78

Table 3.15 Actual and true scale factor for masonry materials

Description Prototype Model Scale Factor

Actual True

Masonry Unit Dimensions (length x width x thickness); inch; (mm)

8.7x4.2x2.75 (222x107x70)

2.2x1.1x0.67 (56 x27x17) 4.0 4.0

Compressive Strength of Masonry Mortar; psi; (MPa) 997.3 (6.9)

238.8 (1.7) 4.2 4.0

Compressive Strength of Masonry unit, psi; (MPa) 2338.0 (16.1)

634.8 (4.4) 3.7 4.0

Density of Masonry unit, lb/ft3; (kN/m3) 101.0 (15.9)

98.0 (15.4) 1.03 1.0

Compressive Strength of Concrete, psi; (MPa) 1500 (10.3)

367 (2.53) 4.1 4.0

Yield Stress of Reinforcing Steel, psi; (MPa) 94,500 (652.0)

29,000 (200.0) 3.3 4.0

3.4.2 Masonry Assemblage

Table 3.16 summarized the results of prototype and model masonry assemblage. It is worth

mentioning that the mechanical properties of model masonry assemblage is representing the

actual model brick (Model Brick No. 1, 56 x 27 x 17)

Table 3.16 Actual and true scale factor for masonry assemblage

Description Prototype Model Scale Factor

Actual True

Compressive Strength of Masonry,ƒk, psi; (MPa) 839.6 (5.8)

278.6 (1.92) 3.01 4.00

Tensile Strength (shear) of Masonry,ƒtk, psi; (MPa) 51.27 (0.35)

31.97 (0.22) 1.60 4.00

Modulus of Elasticity of Masonry, E, ksi; (GPa) 288.0 (1.98)

46.28 (0.32) 6.22 4.00

Shear Modulus of Masonry, G, ksi; (GPa) 28.11 (0.19)

16.53 (0.11) 1.70 4.00

It is observed that the mechanical properties of masonry materials are satisfactorily modeled,

the modeled masonry assemblage showed a higher trend. This could be attributed to the

increase in bond strength in the model masonry (Calvi, G. M., et al., 1996). It could be

concluded that, however, properties of masonry materials are very well scaled, the

mechanical properties of model masonry have not ben scaled as required by complete model

similarities. The actual scale factor should be used for extrapolating model masonry results to

prototype masonry.

79

CHAPTER 4 EXPERIMENTAL PROGRAM: SHAKE TABLE TEST

4.1 INTRODUCTION

In order to determine the behavior of typical masonry building by testing small scale model

buildings, the requirements of strength as well as dynamic characteristics must be fulfilled. In

the case of complete model similitude laws, as described earlier, the compressive stresses in

the walls should be scaled so that failure mechanism in prototype and model is same. For the

dynamic behavior to be same, mass and stiffness requirements should be fulfilled.

The selection of typical Pakistani masonry building, fabrication of different phases of model

buildings, calculation of additional load to simulate floor finishing, instrumentation and data

acquisition and finally the testing procedure is discussed in this chapter. The chapter is

divided into ten sections. Pullout test is conducted on model aluminum bar is presented in

section 4.4. Different parameters of selected ground motion are discussed in section 4.9.

4.2 TYPICAL PAKISTANI MASONRY BUILDING

The diversity in materials of construction and configuration is high in Pakistani residential

buildings. Solid fired clay brick, solid and hollow concrete block, adobe brick, and mud is

used for the construction of residential buildings in both rural and urban areas. The fired clay

brick load bearing walls are typically double leaf of 9 inch (229mm) thickness, are laid in

English bond. 4½ inch (115 mm) thick walls, laid in running bond are typically used as non-

load bearing walls including boundary and parapet walls. Solid and hollow concrete blocks,

typically of 12 x 8 x 6 inch (30.5 x 20.3 x 15.2 cm) size are laid in stretcher bond to construct

load bearing walls or non-load bearing infill in frame structure. In rural areas adobe brick

wall of the same size as burnt brick walls or mud walls of comparatively larger size is used

for single story load bearing walls.

Cement-sand, cement-Khaka (stone dust)-sand or mud mortar is used for the construction of

masonry walls. The proportion of mortar varies from place to place and from building to

building and also varies with the wall thickness. Comparatively weak mortar is used in 9 inch

80

thick wall than 4½ inch thick wall (half brick thickness). In rural area mud mortar is used for

the construction of walls.

Floor slab is mostly rigid reinforced concrete 5 or 6 inches (127 or 152 mm) thick. Wooden

and/or steel truss with galvanized iron (GI) sheet is used in hilly terrain for roofing. Steel W-

section girder and T-section supporting fired clay tiles and heavy 6-8 inches (152-203 mm)

thick mud load is also used for roofing in some areas. Foundation is either of stone masonry,

stepped brick masonry, plain concrete or in very rare cases of reinforced concrete. The

masonry buildings are typically of one to two stories high. However, three and four stories

masonry building are available in old urban areas. The story height is 10 to 12 ft (3.0-3.7 m).

For this study, up to 64 building drawings have been collected from Peshawar, Abbottabad

and Mansehra. The plot area for these buildings ranges from 5-7 Marlas (1360-1904 sq.ft or

126.0-177 m2). The buildings represent single and double story brick masonry residential

buildings. All load bearing walls are typically of 9 inch (229 mm) thickness. The drawings

have been analyzed on the basis of wall density ratio in both orthogonal directions. Finally a

single and double story typical brick masonry building have been selected for their wall

density ratio close to mean wall density ratios.

Table 4.1 gives range of wall density ratios in both orthogonal direction for single and double

story buildings and Table 4.2 gives wall density ratio of the selected single and double story

building. Figure 4.1-4.3 shows the selected prototype buildings. The dimensions of the model

building have been slightly reduced in both directions to accommodate the model on the

shake table. However, wall density ratio has not been significantly reduced. The non-load

bearing walls are not considered in the model building construction.

Table 4.1 Wall-density ratios of buildings

S. No. Type of Building Wall-Density Ratios

Long Direction Short Direction

1 Single-Story Buildings 4.55% to 10.34% 2.81% to 7.98%

2 Double-Story Buildings - Ground Floor 3.92% to 12.78% 2.28% to 7.30%

Double-Story Buildings - First Floor 3.00% to 9.69% 1.86% to 6.03%

81

Table 4.2 Wall-density ratios of selected buildings

S. No. Type of Building Wall-Density Ratios*

Long Direction Short Direction

1 Single-Story Buildings 8.16 5.64

2 Double-Story Buildings - Ground Floor 8.17 3.87

Double-Story Buildings - First Floor 7.81 5.99

Figure 4.1 Typical single story prototype building

82

Figure 4.2 Ground floor of typical double story prototype building

83

Figure 4.3 First floor of typical double story prototype building

The building has been confined according to the requirements of EC8. Tie columns, 9x9

inch, have been provided at the wall junctions and 9x6 inch (229x152 mm) have been

provided at the end of the walls. All doors and windows openings greater in size than 4x4 ft

(1.22x1.22 m) are confined with 9x6 inch (229x152 mm) confining element. A 9x6 inch

(229x152 mm) bond beam has been provided over wall at the lintel level. Tie columns are

provided at maximum horizontal spacing of 13 ft (3.96 m). The confining elements are

84

reinforced with 4#4 longitudinal bars. # 3 bar stirrups are provided at 6 inch (152 mm) in the

horizontal and vertical confining element.

The prototype building dimensions have been reduced by a scale factor of 4. Commercially

available 3.1 mm aluminum wire has been used as model reinforcement in the confining

element to simulate #4 longitudinal bars. The #3 bar stirrups have modeled with 1 mm mild

steel wire woven twice to make the effective diameter of 2 mm. Figure 4.4-4.6 illustrate the

confining element location in single and double story building.

Figure 4.4 Single story confined masonry model building

85

Figure 4.5 Ground floor double story masonry model building

86

Figure 4.6 First floor double story masonry model building

4.3 FABRICATION OF TYPICAL PAKISTANI MASONRY BUILDING

In the subsequent sections, the different stages of construction of model are discussed.

4.3.1 Foundation Pad

The model buildings have been constructed on foundation pad. The foundation pad has been

designed to support shear and flexure action during lifting operation of the specimen and of

the overhang portion when the specimen is fixed with the shake table top. The pad is 5 inches

(127 mm) in thickness and is reinforced with # 3 deformed reinforcing bar @ 6" c/c in both

87

directions. Through holes, 0.51 inch (13 mm) in diameter, were provided in the foundation

pad for fixing model building with the table top (shake table platform) by steel bolts. Model

rebars were tied with the foundation steel prior to concrete pouring. While in the other case

holes have been drilled in the concrete, rebars were then fixed in the holes with epoxy resin.

In the former case there was problem of positioning of flexible modeled bars during concrete

pouring. Pull out test has been carried out for the later case (section 4.4). U-type hooks were

also provided near four corners for lifting purposes. The different stages of construction of

foundation pad are shown in figure 4.7-4.8.

Figure 4.7 Through holes in reinforced concrete foundation pad

Figure 4.8 Model rebars embedded in foundation concrete

88

4.3.2 Masonry Walls

Markings have been made for walls and tie columns on the foundation pad. The foundation

was roughened with chisel for proper bond between foundation pad and first layer of bricks.

Special arrangement had been made for keeping walls aligned. Plumbness of the walls is

checked with water level. 2-3 mm joint thickness is maintained throughout the model

building construction. The bricks were laid in English bond. At the end and at the junction of

walls toothings were provided with 1/4th of brick projection. The practice of construction of

the prototype was respected in the construction of the model buildings. Figure 4.9 shows

construction of wall and figure 4.10 shows under construction model with toothing at the end

and junction of walls.

Figure 4.9 Under-construction ground story wall

89

Figure 4.10 Toothing at the end and walls junction

4.3.3 Confining Element

Tie columns reinforced with 4 bars are provided at the specified locations. The bond beams

are provided when all the walls are erected up to lintel level (7 ft/2.1 m from floor level). The

longitudinal reinforcement of tie columns has been anchored in the foundation slab. The

reinforcement of tie columns and beams are tied together with binding wire. The longitudinal

reinforcement of tie beams at the end of wall are provided 90-degree hook. Micro concrete

has been poured into the tie column after the wall has been constructed. However, in this case

the micro concrete is manually vibrated with a steel wire for better filling in the wall

toothing, in the case of prototype construction good consistency of concrete as well as

mechanical vibration is required. Figure 4.11-4.16 show modeled rebars, their fixing during

construction of model, concrete pouring in modeled confining element.

90

Figure 4.11 Fabrication of stirrup for bond beam and tie column

Figure 4.12 Model bond and floor beam reinforcement

91

Figure 4.13 Rebars fixing for floor beam

Figure 4.14 Micro concrete pouring in tie column

92

Figure 4.15 Tie column after removal of form work

Figure 4.16 Concrete pouring in floor beam in double story model

4.3.4 Floor Slab

Floor slab has been cast after walls and tie columns have been constructed. The slab

reinforcements have been fabricated and fixed at desired spacing. Sufficiently rigid farm

work has been erected. Polyethylene sheet is provided over the plywood form work as to

prevent absorption of water from micro concrete. The slab reinforcement mesh has been

brought and positioned on slab form work. The tie column’s reinforcements have been bent

with the roof slab reinforcement before concrete pouring. The slab concrete has been cured

for about 7 days. The slab form was removed after 28 days of concrete pouring. In the case of

93

ground floor of the double story model, the form work was kept until the second floor (roof

slab) has been cast. After the slab was sufficiently strong, marking was made for the location

of additional steel masses, simulating floor finishing and live load, and holes were drilled in

the slab. Figure 4.17 and figure 4.18 shows floor slab reinforcement and concreting.

Figure 4.17 Slab reinforcement prior to concrete pouring

Figure 4.18 Concrete pouring for single story floor slab

94

4.4 PULL OUT TEST

In order to check the adequacy of model rebar anchorage in foundation pad fixed in drilled

holes by epoxy resin, pull out tests have been carried out. The tests were also aimed to check

the anchorage of the bar in tie columns and bond beams. However, there exist a standard test

method, ASTM A 944-99 for comparing bond strength of prototype steel reinforcing bars to

concrete using beam-end specimens, a simplified pull out test method has been designed for

testing model rebar anchorage.

Two types of mortar, cement-sand (CS 1:6) and cement-lime-sand (CLS 1:1:5), and two

types of bar anchorage were used. In one type straight bar was anchored in fresh concrete

with anchorage length of 3.75 inch (95 mm), calculated according to ACI Code 12.2.3. In

other type hook bar was anchored with hook length of 12 times diameter of bar. Three

specimens were prepared of each mortar and anchorage type. Three specimens were prepared

fixing bar by epoxy resin in a drilled hole. In such case the anchorage length was 1½ ".

Figure 4.19 and figure 4.20 show pull out specimen and test set up. Figure 4.21 illustrate

different pull out specimens and anchorage details. Table 4.3 gives failure mode and stress at

pulling during pull out.

Figure 4.19 Pullout test specimens

95

Figure 4.20 Pullout Test Set up

33 4"

3"

6"

6"

A A

PLAN

SECTION A-A

STRAIGHT WIRE INMODEL CONCRETE

3mm Ø ALUMINUM WIRE

33 4"

3"

6"

6"

A A

PLAN

SECTION A-A

HOOKED WIRE INMODEL CONCRETE


112"

11 2"

3"

6"

6"

A A

PLAN

SECTION A-A

STRAIGHT WIRE INPROTOTYPE CONCRETE


EPOXY

DRILLEDHOLE

Figure 4.21 Details of pullout Test Specimens

96

Table 4.3 Pull out test results

Specimen Dia of Wire

(in)

Area of Wire

(sq. in)

Stress at pulling (% age of

Yield Strength) Failure Mode

Straight Bar (Embedment length = 3.75" or 95 mm), 1: 6 micro concrete

1 0.125 (3.18) 0.0123 (7.94) 95% Pulled out

2 0.125 (3.18) 0.0123 (7.94) 97% Pulled out

3 0.125 (3.18) 0.0123 (7.94) 90% Pulled out

Hooked Bar (Embedment = 3.75" or 95 mm & Hook length = 1.5" or 38 mm), 1: 6 micro concrete

1 0.125 (3.18) 0.0123 (7.94) 122% Wire Broke

2 0.125 (3.18) 0.0123 (7.94) 139% Wire Broke

3 0.125 (3.18) 0.0123 (7.94) 139% Wire Broke

Straight Bar (Embedment length = 3.75" or 95 mm), 1: 1: 5 micro concrete

1 0.125 (3.18) 0.0123 (7.94) 80% Pulled out

2 0.125 (3.18) 0.0123 (7.94) 85% Pulled out

3 0.125 (3.18) 0.0123 (7.94) 90% Pulled out

Hooked Bar (Embedment = 3.75" or 95 mm & Hook length = 1.5" or 38 mm), 1: 1: 5 micro concrete

1 0.125 (3.18) 0.0123 (7.94) 130% Wire Broke

2 0.125 (3.18) 0.0123 (7.94) 139% Wire Broke

3 0.125 (3.18) 0.0123 (7.94) 139% Wire Broke

Straight Bar (Embedment length = 1.5"or 38 mm) with epoxy

1 0.125 (3.18) 0.0123 (7.94) 130% Wire Broke

2 0.125 (3.18) 0.0123 (7.94) 130% Wire Broke

3 0.125 (3.18) 0.0123 (7.94) 100% Pulled out

It was observed that all the hooked bars in both types of mortars ruptured. The straight bars,

however, pulled out but the stress at the pulling was more than 80 % of yield strength in both

mortar specimens. Two out of three bars ruptured and the third pull out at 100 % of yield

strength in case of epoxy fixed bar specimens. It is worth mentioning that the age of micro

concrete at testing was 14 days. Compressive strength of micro concrete CS 1:6 and CLS

1:1:5 at 14 days was 480 psi (3.3 MPa) and 250 psi (1.52 MPa) respectively. The bond

between micro concrete and modeled wire would have increased with age and strength of

97

concrete, the hooked bars and epoxy fixed bars would develop the yield strength with out

pulling.

4.5 DESIGN OF SLAB AND FLOOR BEAM REINFORCEMENT

Floor slab and floor beams have been designed as per ACI-code. The slabs are designed for

supporting live load of 40 psf (1.92 kN/m2), floor finishing load of 35 psf (1.67 kN/m2) and

self weight of the slab. The minimum thickness calculated is 5 inch (127 mm) for both single

and double story building. Negative reinforcements have been provided in top of the slab

over all internal walls. Floor beams have been provided in the ground floor of double story

building. The beams have been designed for supporting ground floor load, upper story wall

load and self weight of the beam. Figure 4.22-24 illustrate the reinforcement of single and

double story buildings. Figure 4.25 shows cross sections of floor beam (beam 1) at mid span

and near support, and reinforcement details of confining element.

98

Figure 4.22 Slab reinforcement details of single story building

99

Figure 4.23 Slab reinforcement details of ground floor double story building

100

Figure 4.24 Slab reinforcement details of first floor double story building

101

Figure 4.25 Reinforcement details of floor beams and confining elements

4.6 ADDITIONAL FLOOR MASSES

In order to simulate the live load and floor finishing, additional masses have been attached.

The masses have been distributed and attached with floor slab in such a way as to fulfill the

requirements of compressive stresses in the walls but would not affect the dynamic

characteristics of the model.

The masses have been calculated on the basis of actual densities of the prototype and model

materials. The densities of materials are determined by measuring actual weight and

dimensions of prototype and model walls.

Prototype Masonry = 101.0 pcf (15.87 kN/m3)

Model Masonry = 95.31 pcf (14.98 kN/m3)

Micro Concrete = 98.83 pcf (15.53 kN/m3)

102

However, the densities of prototype reinforced concrete and floor finishes are assumed to be

150 pcf (23.57 kN/m3) and 140 pcf (22.0 kN/m3) respectively. In the calculation of additional

masses for the model building, self weight of the floor slab and 3 inch floor finishes (35 psf)

has been considered. The mass of wall to slab ratio of prototype and model is adequately

correlated (table 4.4). The mass of slab includes additional masses, floor finishes and self

weight of slab.

Table 4.4 Correlation of prototype to model

Prototype Mass (lb) Model Mass (lb)

Wall, (A) Slab (B) A/B Wall, (A) Slab (B) A/B

Single Story 57,267.0

(25,983.2)

63,280.0

(28,711.4) 0.90

841.6

(382.4)

877.8

(398.3) 0.96

Ground floor, Double Story 123,037.0

(55,824.4)

69,981.3

(31,752.0) 1.76

1,808.2

(820.4)

963.2

(437.62) 1.88

First Floor, Double Story 59,880.4

(27,169.0)

76,160.0

(34,555.4) 0.79

880.0

(400.0)

1,010.8

(459.2) 0.87

Circular steel weights 22 lb (10 kg) each is used as additional mass. The masses are

uniformly distributed and fixed by nut and bolts with model slab so that no movement was

possible during shaking of the model. The location of additional masses on the slab is

illustrated in figure 4.26-4.28. The masses can also be seen in figure 4.29-4.30 after fixing

with models.

103

Figure 4.26 Additional masses on single story model

104

Figure 4.27 Additional masses on ground floor of double story model

105

Figure 4.28 Additional masses on first floor of double story model

106

Figure 4.29 Additional masses on single story model

Figure 4.30 Additional masses on double story model

4.7 EARTHQUAKE SIMULATOR

Earthquake Engineering Center (EEC), N-W.F.P University of Engineering and Technology,

Peshawar has 5.0 x 5.0 ft (1.5 m x 1.5 m) single degree of freedom and 20.0 x 20.0 ft (6.0 m

x 6.0 m) six degree of freedom earthquake simulators (shake tables). At the time of this study

the later facility was under construction, therefore, the reduced scaled models were tested on

single degree of freedom shake table (figure 4.31).

107

Figure 4.31 Single degree of freedom earthquake simulator (shake table)

The seismic simulator consists mainly of 5 ft x 5 ft (1.5 m x 1.5 m), 2.5 inch (64 mm) thick

aluminum table and an actuator. The table moves to and fro on a rail. The actuator drives the

table, is connected at one end with the table and the other end is fixed with a reaction arm.

The actuator is displacement control. Desired acceleration time history is fed in the computer

in the control room which is converted to displacement time history by controller to drive the

actuator. An external accelerometer connected with table and a internal LVDT is used for

feedback. The detailed description of the shake table, its components and controller is given

in Appendix B.

4.8 INSTRUMENTATIONS AND DATA ACQUISITIONS

Global response of the model building is captured through two types of instruments,

accelerometers and displacement transducers. The accelerometers are used to measure

absolute response acceleration and displacement transducers are used to measure relative

displacement response of the model. The following sections provide details of the

instrumentation plan and data acquisition.

4.8.1 Accelerometers

Two types of accelerometers were used in this study. 10g capacity accelerometers were

connected at mid depth of floor slab to capture model response in the direction of shaking. A

total of 4 accelerometers were used in single story model connected at the floor slab at

108

location of the four in-plane walls. Four accelerometers were also used in the double story

model building, two connected at each floor at the location of in-plane exterior walls. A 2g

capacity Dytran accelerometer was used to capture response of base slab and to compare the

result with the table top for possible relative slip. An additional accelerometer was also

connected at the bottom side of the shake table top to measure table acceleration. The

instrumentation plans for single and double story model are shown in figure 4.32-4.34.

Figure 4.32 Instrumentation details of single story model

109

Figure 4.33 Instrumentation details of double story model (elevation)

110

Figure 4.34 Instrumentation details of double story model (plan)

4.8.2 Displacement Transducer and Reference Frame

String pot displacement transducers were used to measure the relative displacement response

of the models. The displacement instruments were connected at the same locations where

accelerometers were connected in both single and double story model as shown in figure

4.32-3.34. The string pot transducers were connected with specially designed reference frame

erected off the table. Tube steel section was used in the design and fabrication of the

reference frame. The frame is designed and fixed on strong floor in such a way that minimum

floor noise has been transferred to the instruments. For this purpose an accelerometer was

also installed on the frame to measure noise level during testing operation. Reference reframe

is shown in figure 4.35

111

Figure 4.35 Reference frame for displacement transducer.

4.9 GROUND MOTION TIME HISTORY

Kobe 1995 North-South component earthquake acceleration record has been used for the

motion of shake table. The peak acceleration of the earthquake record is 0.833 g. The record

is originally of 50 second duration but first 30 second strong motion record is taken for shake

table motion. The record is used on the basis of its predominant period of 0.36 second.

As complete model similitude requirements are to be fulfilled, therefore, the earthquake

record is to be compressed in time duration by square root of scale factor but the amplitude

or acceleration of the record is not scaled. The duration and peak acceleration of the modeled

record becomes:

Prototype:

Duration of earthquake record = 30 sec,

Peak Acceleration = 0.833 g

Model:

Duration of earthquake record = 304

= 15 sec,

Peak Acceleration = 0.833 g

112

The prototype and model earthquake accelerogram is shown in figure 4.36 and figure 4.37

respectively.

Since the behavior of the models is to be assessed from low level of shaking to high level, the

shake table motion is applied in increasing increments. The different intensities of shaking

applied on the model are 5 %, 10 %, 20 %, 40%, 60%, 80%, 100%, 125%, 150%, 175% and

200%. The different intensities of shaking is chosen to have enough points for plotting base

shear to drift ratio curve and assessing the response modification and ductility factor.

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Time (see)

Acc

eler

atio

n (g

)

Prototype Acceleroram

Figure 4.36 Prototype acceleration time history

113

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Time (see)

Acc

eler

atio

n (g

)

Model Accelerogram

Figure 4.37 Model acceleration time history

4.10 TESTING PROCEDURE

As discussed earlier the models were constructed on the reinforced concrete slab. Hooks

were provided at the corners of the base slab. Special arrangements were made to lift (figure

4.38) the models from its construction location to the shake table by 20 tonne overhead

crane. The model was fixed to the table top with nuts and bolts. The roof slab was hanged

with the overhead crane by belt in such a way that it would hold the slab in case of model

collapse and to avoid instrument damage and would not interfere in the dynamic

characteristics of the model shaking.

114

Figure 4.38 Lifting operation of double story building

Both single and double story models were tested in their weak axis. The models were given

different motions in increasing increments. Before each incremental motion, a free vibration

test was carried out to find natural frequency and coefficient of viscous damping ratio of the

model by hitting the model with impact hammer. An 18 inch (46 cm) wooden piece was

placed on the center of the top slab and then the wooden piece was hit with steel hammer.

After analyzing displacement and acceleration data, it was found that the frequency and

damping ratios were not representative of the model. Then a small amplitude forced motion

was given after each test run for dynamic characterization. The motion was given manually

to the shake table. Fourier amplitude spectra were used for determining the dynamic

characteristics.

The response of the models was measured with the help of accelerometers and displacement

transducers as explained earlier. All the accelerometers and string pots were connected with

data acquisition system. The instruments were checked before the start of the first test run by

giving low level excitation to the shake table and observe their functioning qualitatively. For

each test run data was collected for 40 second. After each test run, cracks were marked on the

model and photographed. The cracks were also mapped on the drawing. Two video cameras

were used to capture the response of the model during shaking.

115

CHAPTER 5 SHAKE TABLE TEST RESULTS

5.1 INTRODUCTION

In this chapter the measured response of reduced scale model on shake table test has been

analyzed to evaluate the behavior of single and double story brick masonry building. The

chapter is basically divided into five sections. In section 5.2, the behavior of single story

model and data analysis has been discussed. The section is subdivided into nine sections. The

general condition of single story model before commencing shake table test and then damage

propagation and failure mechanism during different shake table tests with increasing

intensity has been discussed. Base shear and story rotation evaluated on the basis of

measured response acceleration and response displacement is presented. The response

modification factor for single story model evaluated from global ductility factor and elastic

response has also been presented.

In section 5.3, the behavior of double story model has been discussed. In section 5.4, the

seismic resistance parameters of single and double story model has been extrapolated to

prototype building.

In section 5.5 the behavior of single and double story model has been compared.

5.2 SINGLE STORY MODEL BUILDING

As explained in the preceding sections, visual observations were made after each test run for

damage propagation. The internal and external walls of the models were white washed before

start of the test. The cracks were marked on the model and photographs were taken after each

test run. The cracks were also mapped on the drawing after each test run. Video was prepared

during each test run and after the test.

For the reporting purposes, the out of plane and in plane walls were divided in different grids

as shown in figure 5.1. Walls are designated after grids lines. For example, walls parallel to

116

grid A, B, C and F are designated a wall A, wall B, wall C and wall F. Similarly, walls

parallel to grid 1, 5, 6 and 12 are designated as wall 1, wall 5, wall 6 and wall 12.

Figure 5.1 Grid lines-single story model

5.2.1 Condition of Model before Test

The model was carefully lifted with the help of overhead crane from the location of its

construction and fixed on the shake table. The model was thoroughly observed for any cracks

before lifting and white washing operation. Horizontal hairline cracks between first and

second layer of bricks in the out-of-plane wall 12 were observed. This could be because of

the shrinkage of the micro-concrete and deflection of the floor slab. Hairline cracks were also

observed on the upper side of the roof slab. The cracks marked with black marker are shown

in figure 5.2. After the model has been fixed, it was again inspected for any damage during

lifting and fixing operation. However, no damage has been observed.

117

Figure 5.2 Hairline cracks in roof slab and out-of-plane walls before test

5.2.2 Out of plane Walls

The out of plane walls were comparatively less damaged during shake table tests. There were

no cracks in the out of plane walls (grid 1, 5, 6 & 12) until test run R60. During test run R60

horizontal hairline cracks were observed in wall 1 (panel between grid A and B) almost at

mid height between bond beam and foundation pad. A horizontal hairline crack was also

observed in the bottom course (panel between grid A and B), propagating in zig zag fashion

towards tie column. The wall on grid 12 has developed horizontal hairline cracks in the

second last course (panel between F and C). In the subsequent test run 80, a new vertical

crack formed between masonry and tie column (1B) interface propagating from top slab

towards bond beam. In the same test run, a shear stepped crack was observed on right side of

window in wall 6.

During test run 125, some new cracks formed in both out of plane walls 1 and 12.

Propagation of existing cracks was also observed. A hairline cracks developed at second

course from the slab in wall 1. In the test run R175, the shaking was so intense that slab

corner (where the accelerometer was also installed), at tie column A1 location, cracked and

Hairline

Cracks

118

subsequently disintegrated. The sliding of slab at existing horizontal cracks could be noticed

in grid 1 and 12 (figure 5.3 and 5.4). The internal wall at grid 5 could not be observed during

the testing phases. Figures D1-D9 in Appendix D shows schematic diagrams of crack

propagation during each test run. The figures show propagation of the existing cracks and

newly developed cracks in each test run. However, the overall damage to walls has been

presented in the last test run.

Figure 5.3 Sliding of roof slab and cracks in out of plane wall 1 after final test run

Figure 5.4 Cracks in out of plane wall 12 after final test run

Cracks in wall 1

Cracks in wall 12

119

5.2.3 In-plane Walls

The in plane walls were severely damaged at the end of test. Crushing of concrete in the tie

column, falling and crushing of brick and separation of masonry walls from the tie columns

were observed. The reinforcement in the tie column buckled at the beam-column joints.

However, all the in-plane walls severely damaged, the confining element prevented the in-

plane walls from disintegration and model from collapse. Damaged external walls at the end

of shaking table test are shown in figure 5.5 and 5.6. Figures D10-D15 in Appendix D shows

schematic of the cracks propagation in the in-plane walls during shake table test.

Figure 5.5 Damage to in-plane wall (grid A) at the end of test

Figure 5.6 Damage to in-plane wall at grid C and F at the end of test

120

In the in-plane walls no cracks have been observed until test run R60. During the test run a

hairline stepped shear cracks were observed originating from bottom of right window and

propagated upward towards tie column (grid A). Another crack during the same test run was

also observed near column A5 between roof slab and bond beam. However, during test run

R80 some cracks have been observed in Grid C and F. An inclined shear crack was observed

in wall C between roof slab and bond beam. Another hairline crack was observed almost at

mid height between bond beam and base slab. A horizontal hairline crack was also observed

in Grid F. No significant new crack was observed in the subsequent test run until R125,

except the propagation of the old crack.

The model was seriously damaged during test run R125. Major shear cracks were developed

wall of the model. Inclined stepped shear cracks propagating from bottom corners of the

window in wall A were observed running towards bottom corners of the tie columns.

Horizontal cracks have also been observed propagating from the two windows. The cracks

developed in a scissor crack in the pier between the windows, which also pass through the tie

column (A5) concrete. Vertical crack at the interface of tie column A12 and masonry wall

was also observed. Inclined shear cracks following mortar joint appeared in the in-plane

walls having doors. The cracks propagated from the top and bottom end of the door confining

element (tie column) and join almost at the center of the wall panel. These types of cracks

were observed in all internal and external in-plane walls. The cracks also shear micro-

concrete at the top and bottom end of the tie column. Spalling of concrete cover at the top of

tie column was also observed.

During test run R175, the model was significantly damaged. Some new cracks were

observed. Existing cracks opened up and propagated. Falling of part of already cracked

masonry from the sides of the window was observed (wall A). Opening and closing of

existing cracks could be clearly seen in the close up video clips. Because of the increased

drift demand, the concrete at the top and bottom of tie column crushed. The rebars buckled at

this location. Bricks near top and bottom joint of tie column were also crushed. Separation of

tie column and masonry wall was also observed. Horizontal crack at the roof level could also

be seen.

121

However, the in-plane walls were heavily damaged, no out of plane failure of walls were

observed. This could be attributed to the effect of confining element. The test has been

terminated after the heavy damaged to in-plane walls, crushing of concrete and buckling of

steel in the confining element.

5.2.4 Characteristics Parameters of Shaking Table Motions

Maximum acceleration and displacement of shaking table motion are compared with that of

input model accelerogram in table 5.1. It is observed that the shaking table satisfactorily

simulated the acceleration record. However, the measured acceleration is comparatively

larger than the input model acceleration. Because of the malfunctioning of the shake table

during test run R175, base acceleration of 2.01g was recorded. As the controlling parameter

was acceleration, no clear trend was seen in the shake table measured displacement and input

displacement. The input displacement is calculated after twice integrating the input

acceleration. However, the input motion could not be exactly achieved by some technical

deficiencies; the aim of the reduced scale model would be achieved. The small difference

between input and the achieved motion is inevitable and were experienced in research on

simple simulators (Roko Zarnic et al 2001). The comparative difference between input and

shake table motion could be attributed to the model-platform interaction, friction between the

moving parts of the testing facility and dynamic characteristics of the system (Tomazevic

1992).

Shake table acceleration could not be recorded above 2.0g because upper limit of the

accelerometer installed on the shake table and base slab was reached. The capacity of the

accelerometer connected with table top for controlling actuator was 10g, however, only the

maximum value could be recorded. The displacement and acceleration time histories,

recorded during the shaking table test are presented in figure C1-C100 in appendix C.

122

Table 5.1 Characteristic parameters of shake table motion

Test Run

Input Model Accelerogram Shake Table Motion

Max. Acceleration

(g)

Displacement

(mm)

Max. Acceleration

(g)

Displacement

inch (mm)

5 0.0417 0.092 (2.34) 0.0603 0.216 (5.485)

10 0.0833 0.184 (4.679) 0.1073 0.213 (5.409)

20 0.1666 0.368 (9.359) 0.1955 0.282 (7.161)

40 0.3332 0.737 (18.718) 0.4853 0.716 (18.181)

60 0.4998 1.105 (28.078) 0.5761 1.018 (25.849)

80 0.6664 1.474 (37.437) 0.9659 1.139 (28.922)

100 0.8330 2.176 (55.276) 0.8825 1.757 (44.64)

125 1.0413 2.303 (58.495) 1.0433 2.387 (60.637)

150 1.2495 2.764 (70.194) 1.3192 2.538 (64.471)

175 1.4578 3.224 (81.893) 2.0100 2.778 (70.565)

60R 0.4998 1.105 (28.078) 0.4000 1.018 (25.849)

100R 0.8330 2.176 (55.276) 0.8200 1.834 (46.595)

150R 1.2495 2.764 (70.194) 1.4900 -

5.2.5 Frequency and Damping ratio

Natural frequency and coefficient of viscous damping has been determined before the start of

test and after each test run. The natural frequency after the initial few test runs has been

determined by hitting middle of the top slab with hammer. A wooden strip placed in contact

with the middle of the slab, was hit with the steel hammer as direct impact on the slab could

have damaged the slab. However, after observing impression of the wooden strip on the slab

and masonry, a small impulse was given after each test run to determine the natural

frequency of vibration and coefficient of viscous damping. Table 5.2 gives natural frequency

and damping ratio of single story model. The natural frequency has been determined by

plotting fourier amplitude of the acceleration recorded at the top of the slab. Fourier

amplitude spectra before the start of test and after test run R175 has been shown in figure 5.7

and 5.8. Half-power band width method (Chopra, A, K., 2004) was used to estimate

coefficient of equivalent viscous damping, ζ.

123

2b a

n

f ff

ξ−

= (5.1)

Where:

fa & fb = frequencies on either side of the resonant frequency at which amplitude is

1/√2 times the resonant amplitude, and fn is the resonant frequency.

Table 5.2 Frequency and coefficient of viscous damping

Test Run Frequency, Hrz Coefficient of

Viscous Damping (%)

R00 30.11 3.98

R010 31.35 4.18

R020 29.34 4.13

R040 27.54 5.30

R060 25.66 5.35

R080 21.54 5.89

R100 19.87 6.65

R125 16.33 6.32

R150 16.14 6.68

R175 9.27 10.52

150R 8.34 10.56

0

0.005

0.01

0.015

0.02

0.025

0 10 20 30 40 50 60 70 80

Frequency (Hrz)

Four

ier

Am

plitu

de

Figure 5.7 Fourier amplitude spectra before the start of test

f = 30.11 Hrz,

ζ = 4.98 %

124

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 10 20 30 40 50 60 70 80

Frequency (Hrz)

Four

ier

Am

plitu

de

Figure 5.8 Fourier amplitude spectra after test run R175

It can be seen from the table that frequency decreases and damping ratio increases as the

damage to model increases with the sequence of test run. There is a good correlation between

decrease in frequency and damage propagation. However, the damping ratio increased at the

end of test, there were some readings which were less than their preceding values. The

damping ratio should be interpreted with caution as the values would be larger if obtained

from higher amplitude tests (Clough and Penzien, 1993).

5.2.6 Acceleration Amplification

Acceleration amplification has been determined by dividing maximum response acceleration

with maximum input base acceleration during each test run. The response accelerations of

channel 1 and 2 (figure 4.32) are averaged. The acceleration amplifications are given in table

5.3. The data is plotted in figure 5.9. Acceleration amplification corresponding to test run 80

is not plotted as its acceleration is more than the test run 100. The amplification values of

repeated test run 60R and 150R are also not plotted.

f = 9.27 Hrz,

ζ = 10.52

125

Table 5.3 Floor acceleration amplification

Test Run

Max. Shake Table

Acceleration

(g)

Max. Avg. Response

Acceleration

(g)

Amplification

R5 0.0603 0.0995 1.65

R10 0.1073 0.1307 1.22

R20 0.1955 0.1913 0.98

R40 0.4853 0.5395 1.11

R60 0.5761 0.6391 1.11

R80 0.9659 0.9964 1.03

R100 0.8825 1.0118 1.15

R125 1.0433 1.1672 1.12

R150 1.3192 1.5988 1.21

R175 2.0100 2.7372 1.36

60R 0.4000 0.6391 1.60

150R 1.4900 4.1050 2.76

0.0

0.3

0.5

0.8

1.0

1.3

1.5

1.8

2.0

0.0 0.5 1.0 1.5 2.0 2.5

Peak base acceleration (g)

Peak

top

acce

lera

tion/

peak

bas

e ac

cele

ratio

n

Figure 5.9 Acceleration amplification of single story model

126

The highest amplification of 2.76 was observed during test run 150R. This could be

attributed to the resonance effect. Because at this test run the model has developed sever

damage to the masonry wall. The frequency and stiffness are also decreased at this stage.

However, it is generally expected that the amplification factor decreased as the damaged in

the model is increased.

5.2.7 Torsion Effect

Table 5.4 gives displacement values from channel 10 (at A1) and channel 7 (at F6) and

average of channel 8 and 9 readings. The left and right channels displacements are

normalized with the average of the maximum middle displacements. In the table the average

of the maximum middle displacements measured in all test runs are also given. It is worth

mentioning that left and right displacements are taken at the same instant of time when

maximum middle displacements were taken. All the top displacements are average of six

absolute maximum displacements.

Although, plan irregularity exist in the model, no significant torsional motion has been

observed after the analysis. However, in the last three test run (60R, 100R and 150R) left side

observed more displacement because of the comparatively less rigidity and extensive damage

on this side.

127

Table 5.4 Top slab displacements during different test run

Test Run Normalized Displacement

Average maximum

displacement

inch (mm)

Left

(Channel 7)

Middle

(avg. of channel 8 & 9)

Right

(channel 10) Middle

R5 0.955 1.000 1.003 0.231 (5.867)

R10 0.969 1.000 0.957 0.31 (7.874)

R20 1.050 1.000 1.075 0.729 (18.517)

R40 1.040 1.000 1.013 1.027 (26.086)

R60 1.020 1.000 0.947 1.17 (29.718)

R80 1.031 1.000 0.993 1.729 (43.917)

R100 0.979 1.000 1.000 2.361 (59.969)

R125 1.024 1.000 1.003 2.617 (66.472)

R150 0.996 1.000 0.987 2.814 (71.476)

R175 0.995 1.000 0.990 1.027 (26.086)

60R 1.020 1.000 0.947 1.87 (47.498)

100R 1.010 1.000 0.975 4.805 (122.047)

150R 1.012 1.000 0.998 0.231 (5.867)

5.2.8 Base Shear

Base shear is the sum of inertia forces acting on each story level produced as a result of

excitation at the base. The inertia force at a story level has been evaluated by the mass of

story and acceleration with which the mass has been excited. It has been assumed in

calculating base shear that the model under consideration is characterized by first mode of

vibration. If the shape of the vibration is stable in time, the base shear is given by the

following expression:

i ii

Base shear m a⋅ = ∑ (5.2)

Where:

mi = mass at the ith story level

ai = acceleration of the ith mass

128

The equation 5.2 can also be written as

ii

Base shear S⋅ = ∑ (5.3)

Where:

S3 = m3a3max, is the third story shear

S2 = S3+m2a2max, is the second story shear

Base shear = S2+m1a1max, is the total shear at the base

Base shear has been calculated for the model for each test run by multiplying floor masses

with the average of floor accelerations. Table 5.5 gives average acceleration and base shear

during each test runs. The accelerations corresponding to maximum displacement in channel

# 9 were considered. Floor masses calculated in chapter 4 were used for the determination of

base shear. The floor masses include weight of slab, additional masses attached to the slab

and upper half of the wall mass:

Weight of the floor slab = 436 lb (197.82 kg);

Weight of the upper half of the walls = 787.22 lb (357.18 kg);

Additional weights attached to the slab = 440.8 lb (200 kg)

Weight of the model which would contribute to the inertia forces = 1664 lb (755 kg)

Total weight of the model = 2347.26 lb (1065 kg)

Table 5.5 also gives base shear coefficient and rotation angle of the model. Base shear

coefficient are calculated by dividing base shear with total weight of the model. Story

rotation is calculated by dividing story displacement with story height. The base shear

coefficient is plotted versus story rotation angle in figure 5.10. The graph is called seismic

resistance envelopes.

129

Table 5.5 Base shear coefficient and rotation angle of single story model

Test Run Acceleration

(g)

Displacement

inch (mm)

Story mass

lb (kN)

Shear force

lb (kN)

Base Shear

Coefficient

Rotation

Angle

(%)

5 0.0939 0.0043 (0.1092) 1664.0 (55) 156.27 (0.695) 0.0666 0.014%

10 0.1286 0.0059 (0.1499) 1664.0 (755) 214.02 (0.952) 0.0912 0.020%

20 0.1908 0.0138 (0.3505) 1664.0 (755) 317.56 (1.413) 0.1353 0.046%

40 0.5800 0.0236 (0.5994) 1664.0 (755) 965.13 (4.295) 0.4112 0.079%

60 0.6900 0.0307 (0.7798) 1664.0 (755) 1148.17 (5.109) 0.4892 0.102%

80 0.9883 0.0358 (0.9093) 1664.0 (755) 1644.61 (7.319) 0.7007 0.119%

100 1.2000 0.0484 (1.2294) 1664.0 (755) 1996.82 (8.886) 0.8507 0.161%

125 1.7000 0.0748 (1.8999) 1664.0 (755) 2828.83 (12.588) 1.2052 0.249%

150 2.4000 0.2362 (5.9995) 1664.0 (755) 3993.65 (17.772) 1.7014 0.787%

175 2.6000 0.3543 (8.9992) 1664.0 (755) 4326.45 (19.253) 1.8432 1.181%

150R 1.8000 0.4724 (11.999) 1664.0 (755) 2995.24 (13.329) 1.2761 1.575%

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 1.2% 1.4% 1.6% 1.8%

Story Drift Rotation (%)

Bas

e Sh

ear

Coe

ffic

ient

Figure 5.10 Base shear coefficient and story rotation plot for single story model

Three limit states have been defined to characterize the model. Damage limit state represents

the occurrence of first significant crack and the change (decrease) in the first stiffness of the

130

model. The second characteristic state occurs when the model shows maximum resistance to

the lateral forces. The third state is ultimate state where the model is close to collapse or

where significant damage to structural walls has occurred and the model is beyond repair.

The base shear coefficient and story rotation angle for the three limit states are given in table

5.6.

Table 5.6 Base shear coefficient and story rotation at limit state levels

Description of limit state Base shear

Coefficient

Story Rotation

angle (%)

Elastic limit (R125) 1.205 0.25

Maximum Resistance (R175) 1.843 1.18

Ultimate state (R125) 1.276 1.57

It can be seen from table 5.6 that story rotation angle is 0.25 % at damage or elastic limit

state that is where stiffness of the model significantly changed. The story rotation angle was

found to be between 0.25-0.30 % in test carried out elsewhere on un-reinforced and confined

masonry of two different masonry materials and configuration. However, values of story

rotation varied from 0.28-1.39 % in cases of semi-confined and fully confined masonry

model (Tomzavic, et al. 2004).

5.2.9 Response Modification Factor of Single Story Model

Response modification factor is simply defined as ratio of seismic force when the structure is

fully elastic to the seismic force when structure intrinsic non-linear behavior has been taken

into account. That is the ratio between elastic load, He and ultimate design load, Hu is called

response modification factor, R. The following relation describes the definition.

eHR

Hu= (5.4)

Response modification factor, R can be used to reduce the seismic force determined from

elastic analysis of the structure thereby considering the energy dissipation capacity of the

structure. Therefore explicit non-linear analysis of the structure could be avoided. Response

modification factor can also be evaluated by the following expression:

131

( )µ= −2 1uR (5.5)

Where µu = du/de, is global ductility factor.

The base shear coefficient and story drift ratio relation (figure 5.10) has been idealized by

bilinear curve as shown in figure 5.11. In order to idealize the curve, 20% degradation from

the maximum resistance is taken.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0.0% 0.2% 0.4% 0.6% 0.8% 1.0% 1.2% 1.4% 1.6% 1.8%


Bas

e Sh

ear

Coe

ffic

ient

Figure 5.11 Hysteretic envelope and idealized bilinear relation

The response modification factor according to the definition of global ductility factor is given

below:

du = Ultimate displacement of the idealized bilinear curve = 0.435 inch (11.05 mm)

de = displacement at the elastic limit of the idealized bilinear curve = 0.085 inch (2.15 mm)

Global ductility ratio, µu = 5.13 and,

Response modification factor, R from expression 5.5 = 3.04

In order to determine the response modification factor according to equation 5.4, the reduced

scale building has been modeled in SAP2000. The input and output data has been given in

Appendix E. The model has been analyzed by subjecting it to maximum acceleration


------- Idealised Curve

132

(recorded shake table acceleration during test run R175). The base shear evaluated during the

SAP analysis is given below:

Elastic base shear He = 8410 lb (3816.0 kg)

Experimentally determined base shear Hmax= 4326 lb (1963.0 kg)

Ultimate base shear Hu = 3893.4 lb (1767.0 kg)

Response modification factor, R, according to equation 5.4 = 2.16

The response modification factor given by Eurocode 8 for confined masonry buildings is 2.0-

3.0. Comparing the evaluated response modification factor with that of Eurocode, it could be

concluded that the Eurocode values are adequate.

5.3 DOUBLE STORY MODEL BUILDING

The double story model has been given the same increasing excitation as given to single

story model. The shake table could not produce the desired input excitation. Instruments,

measuring response were removed from the double story model after test run R30. The

model has been excited with increased ground motion until severe damage to in-plane walls

in ground story. The peak shake table acceleration could only be noted as complete time

history file of the shake table motion could not be retrieved. The data analysis and damage

propagation during each test run is discussed in the subsequent sections.

5.3.1 Condition of Model before Test The double story model has been divided into grids in both horizontal directions. The grids in

ground and first floor are shown in figure 5.12. The model has been inspected thoroughly

before white washing. Horizontal hairline cracks have been observed in wall H at the

interface of first floor masonry wall and ground floor slab. A horizontal crack in the second

last mortar joint from the ground story slab was also observed as shown in figure D17,

appendix D. Horizontal cracks of the same nature were also observed in wall 1 in the second

mortar joint from the ground floor slab (figure D18, appendix D). In wall A a horizontal

hairline crack was observed, at the ground floor slab and first floor masonry wall interface

(figure D16). The cracks in walls could be attributed to shrinkage. The model was carefully

133

lifted by overhead crane and fixed on the shake table top. No damage to any wall was

observed during the lifting and fixing operations. The model was white washed prior to

ground shaking.

Figure 5.12 Grid lines- double story model

134

5.3.2 Out of Plane Walls The out of plane walls survived any severe damage or out of plane failure because of the

confining effects. However, separations of masonry wall from tie columns, sliding with floor

and bond beam were observed. Significant out of plane movement could be seen in video

clip, in Wall 9 (towards actuator) of ground story, during the shaking table test

There was no crack in the out of plane walls until Test run 30 except horizontal hairline

cracks as discussed above. A horizontal crack was observed in ground floor at mid height

between bond beam and foundation pad in wall 1 at test run 30. Horizontal hairline crack at

the interface of ground floor slab and first floor masonry wall was also observed in wall 1.

Some horizontal cracks were observed in wall 9 in the ground floor near floor level. A

stepped crack was noted in panel FJ. The crack runs between tie columns. A horizontal crack

at the interface of bond beam and masonry over the beam in the first floor level was also

marked during the test run 30. During last test run (PGA – 3.65g) significant movement of

the out of plane wall of ground floor was observed. In a video clip, wall 9 could be seen

rocking at the base slab and mid height between base slab and ground floor bond beam.

Separation of masonry wall and tie column in panel AB was also visible in the video. Out of

plane sliding of wall 4 in panel EF was observed. However, a few hairline horizontal cracks

were observed in first floor out of plane walls, the damage was relatively small. This could

be also confirmed from its rigid body movement during shaking in the video clips replay.

It could be concluded that some damage to out-plane-walls were observed during strong

shaking (PGA = 3.65g), the confining elements prevented the out of plane failure of the walls

perpendicular to excitation. Figure 5.13 and 5.14 shows cracks in the out of plane walls at the

end of test. Figure D19-D24 of the Appendix D shows schematic of damage propagation to

out-of-plane walls during test runs.

135

Figure 5.13 Cracks in wall 1

Figure 5.14 Cracks in wall 9

5.3.3 In-plane Walls The in-plane walls were severely damaged at the end of testing. External and internal in-

plane walls in ground floor almost collapsed. However, there was no significant damage to

both external and internal wall in first story level at the end of the test. Micro-concrete of

column in the ground floor crushed and model rebars buckled. Crushing of bricks was also

observed in the severely damage zones. Figure 5.15 and 5.16 shows the severely damaged

double story model at the end of test. The schematics of damage propagation to in-plane wall

are shown in figure D22-D27, appendix D. The newly developed cracks and propagation of

136

existing cracks are shown in each figure corresponding to different test runs. The overall

damage to walls are shown in the last test run (figure D26 and D27).

Figure 5.15 Damage to ground floor wall A

Figure 5.16 Damage to ground floor wall F

A hairline crack was observed in in-plane walls during test run 20. Separation crack at the

interface of tie column of window and masonry wall was observed in wall F. A horizontal

crack at the sill level of window was observed, propagating towards window confining

element. A horizontal crack at the interface of bond beam and masonry wall over the beam

was observed to propagate from its pre-testing condition. Hairline cracks at two locations

were marked in wall A during test run 20.

137

First significant damage to in-plane walls were observed during test run R30 when inclined

cracks were developed in ground floor masonry wall. Scissor type cracks were developed in

the ground floor masonry piers of wall A (Grid A). In all the three priers cracks penetrated in

the tie column concrete at the location of bond beam and tie column joint. The cracks from

both directions intersect each other at mid height between bond beam and foundation slab.

Cracks running at the interface of masonry wall and tie column could also be seen, separating

the wall from confining column. Cracks at different locations were also observed in wall F

during test run R30. The cracks in wall F were mostly horizontal. However, the cracks

stepping downward following mortar joint were observed. Short length vertical and inclined

cracks were also marked. At this stage no crushing of brick or micro concrete were

observed.

Wall D (Grid D) was severely damaged during test run R30. Inclined cracks in both

directions were developed. The cracks propagated into tie columns and bond beam, shearing

micro concrete. Cracks at the interface of masonry wall and tie column was also seen.

During the last test run, sever shaking having PGA of 3.65 was observed because of

malfunctioning of shake table. Almost all the ground floor in-plane walls collapsed and/or

severely damaged. Crushing of brick unit was observed in the damage/collapsed walls.

Micro-concrete of the tie column was crushed and model rebars were made visible. The

rebars in the tie columns buckled and deflected out from the original alignment. No

significant crack in the in-plane first floor walls was observed. However, propagation of

existing cracks was noticed. This could be attributed to the concentration of damage to

ground floor and the rigid body motion of the first floor over the ground floor. The

concentration of damage to ground floor could be attributed to soft story effect because of the

more wide openings in the ground floor. The wall density ratio as given in section 4.2 was

3.87 in the ground floor and 5.99 in the first floor.

In closely focused video clips it could be concluded that heavy damage to wall is the result of

crushing of concrete in tie column near joints and/or separation of wall and tie column. The

wall pushed the tie columns out ward and disintegration started at the middle part of the

walls.

138

However, the model did not collapse; the common assumption that the confining elements

would prevent the masonry walls from disintegration did not work. It has been observed

during testing confined masonry walls that the confinement would prevent the wall from

disintegration at certain level of drift. However, at increased demand the separation of

masonry walls from tie column and ultimately collapse of wall could not be prevented.

Horizontal reinforcement in the bed joint, which connect the masonry wall and tie column

certainly improves the inelastic behavior and could prevent the collapse of walls (Tomzvic,

M., et al 1996; IIBA, M., et al 1996). Column confined with enough shear reinforcement

could avoid brittle failure of walls (Kato, H., et al 1992; Salim, A, H., 1982).

It could be concluded that even with strong ground motion; the confining elements prevent

collapse of the masonry building. However, in-plane walls were severely damaged during

strong shaking; the provision of horizontal reinforcement could prevent disintegration of the

masonry walls as reported by other authors during confined masonry walls test. Keeping in

view the economic condition of the people, horizontal reinforcement to connect tie columns

and masonry wall in the ground floor is only recommended. Figure D22-D27 of Appendix

shows schematic of damage propagation during test run.

5.3.4 Characteristics Parameters of Shaking Table Motions

Maximum acceleration and displacement of shaking table motion are compared with that of

input model accelerogram in table 5.7. The shaking table could not satisfactorily produce the

acceleration record. The reasons of the unusual behavior were not verified. However, the

response acceleration and displacements were used to calculate the response behavior of the

model. Instruments were removed from the model as it could be damaged because of the un-

predicted response of shake table motion. Maximum shake table accelerations were recorded

and crack propagation observed during subsequent test run.

139

Table 5.7 Characteristic parameters of shake table motion

Test Run

Input Model Accelerogram Shake Table Motion

Max.

Acceleration

(g)

Displacement

inch (mm)

Max.

Acceleration

(g)

Displacement

inch (mm)

5 0.04165 0.092 (2.34) 0.0638 0.156 (3.97)

10 0.0833 0.184 (4.679) 0.1381 0.235 (5.97)

20 0.1666 0.368 (9.359) 0.3726 0.407 (10.34)

30 0.3332 0.737 (18.718) 0.6356 0.818 (20.77)

60 0.4998 1.105 (28.078) ---- ----

80 0.6664 1.474 (37.437) ---- ----

100 0.833 2.176 (55.276) ---- ----

125 1.04125 2.303 (58.495) ---- ----

150 1.2495 2.764 (70.194) ---- ----

175 1.45775 3.224 (81.893) ---- ----

5.3.5 Torsion Effects Table 5.8 gives displacement values from channel 10 (at A1) and channel 7 (at F6) and

average of channel 8 and 9 readings at the ground floor slab. The response displacement

measured at the first floor slab level by channel 13 to 16 is also given. Displacements

measured by middle channels (14 and 15) are averaged. In the table right and left

displacements are from channel 7 and 10 at ground floor level and 13 and 16 at first floor

level, respectively. The displacements are normalized with the average of middle

displacements. In table the average displacement is also given.

Differences have been observed in the displacement measured at left and right side. This

could be because of torsion in the model and the same is confirmed from the damage

concentration which was more at one side than the other.

140

Table 5.8 Slab displacements during different test run

Test Run Story Normalized Displacement

Maximum

average

displacement

inch (mm)

right Middle left Middle

5 2 1.299 1.000 1.140 0.003 (0.081)

1 1.852 1.000 1.491 0.002 (0.051)

10 2 0.765 1.000 0.859 0.007 (0.19)

1 0.986 1.000 1.346 0.004 (0.103)

20 2 0.986 1.000 0.967 0.013 (0.324)

1 0.995 1.000 1.252 0.014 (0.359)

30 2 0.947 1.000 0.967 0.03 (0.757)

1 1.112 1.000 0.971 0.027 (0.697)

40 2

1

5.3.6 Mode Shape

Mode shapes have been determined by normalizing story displacements with the top

displacements. The story displacement has been obtained by averaging response

displacements measured at four locations in each story corresponding to maximum

displacement in Channel 9. The base displacement is average of two displacements

corresponding to maximum displacement in Channel 9. The mode shapes corresponding to

each test run is shown in figure 5.17.

141

Figure 5.17 Mode shapes corresponding to each test run

The mode shapes represent that the double story model is vibrating in fundamental mode of

vibration. It could be seen from the mode shapes that displacement of the ground story

increases as the model becomes non-linear. This is in agreement with the cracks propagation

and damage concentration in the ground story. However, data was not measured at large

shaking table excitation, the video clips reveals that the first story had rigid body motion.

5.3.7 Acceleration Amplification Acceleration amplification has been determined by dividing maximum response acceleration

with maximum input base acceleration during each test run. The maximum response

accelerations measured at story level during each test run is averaged. The acceleration

amplification and maximum shake table and maximum average response acceleration is

given in Table 5.9. The maximum amplification recorded is 1.88 in the first floor. However

1

0.28

00

1

2

0 0.5 1 1.5

R05

1

0.51

00

1

2

0 0.5 1 1.5

R20

1

0.46

00

1

2

0 0.5 1 1.5

R10

1

0.81

00

1

2

0 0.5 1 1.5

R30

142

response data has not been recorded after test run 30 where the model is significantly

damaged, the acceleration amplification is expected to decrease.

Table 5.9 Acceleration amplification

Test

Run Story

Max. Shake

Table

Acceleration

(g)

Max. Avg.

Response

Acceleration

(g)

Amplification

5 2 0.0638 0.1064 1.67

1 0.1000 1.57

10 2 0.1381 0.2058 1.49

1 0.1883 1.36

20 2 0.3726 0.6988 1.88

1 0.6119 1.64

30 2 0.6356 1.1053 1.74

1 1.0690 1.68

60 2 - - -

1 - - -

5.3.8 Base Shear and First Story Rotation Angle Base shear is the sum of story shear forces. The story shear forces have been calculated by

multiplying masses concentrated at the story with the acceleration measured at the

corresponding story. The story shear for the double story model has been calculated for each

test run by multiplying floor masses with the average of floor accelerations. Table 5.10 gives

average accelerations and base shear during each test runs. The accelerations corresponding

to maximum displacement in channel # 9 were considered. Floor masses calculated in

chapter 4 were used for the determination of base shear. The floor masses include weight of

slab, additional masses attached to the slab and upper half of the wall mass:

Ground Floor:

Weight of the ground floor slab = 492 lb (223 kg);

Weight of the upper half of the walls = 880 lb (399 kg);

Additional weights attached to the first floor slab = 485 lb (220 kg)

143

Ground floor weight = 1857 Ib (842 kg)

First Floor:

Weight of the ground floor slab = 482 lb (219 kg);

Weight of the upper half of the walls = 1808 lb (820 kg);

Additional weights attached to the first floor slab = 485 lb (220 kg)

First floor weight = 2775 lb (1259 kg)

Total weight of the model which would contribute to the inertia forces = 4,632.6 lb (2100kg)

Table 5.10 also gives base shear coefficient and rotation angle of the model. Base shear

coefficient are calculated by dividing base shear with total weight of the model. Story

rotation is calculated by dividing story displacement with story height.

Table 5.10 Base shear coefficient and story rotation angle

Test Run Story

Relative

Acceleration

(g)

Relative

Displacement

inch (mm)

Story mass

lb (kg)

Shear force

lb (kN)

Base Shear

Coefficient

Rotation

Angle

5 2 0.0254 0.0011 (0.0284) 1847.3 (838.2) 47.02 (0.209) 0.010 0.09%

1 0.0608 0.0009 (0.0227)2785.3 (1263.7) 216.4 (0.963) 0.047 0.08%

10 2 0.1132 0.0013 (0.0327) 1847.3 (838.2) 209.24 (0.931) 0.045 0.11%

1 0.1628 0.001 (0.0256) 2785.3 (1263.7) 662.72 (2.949) 0.143 0.12%

20 2 0.1667 0.002 (0.0512) 1847.3 (838.2) 307.97 (1.37) 0.066 0.02%

1 0.1834 0.0013 (0.0335)2785.3 (1263.7) 818.84 (3.644) 0.177 0.17%

40 2 0.4199 0.0031 (0.0782) 1847.3 (838.2) 775.86 (3.453) 0.167 0.26%

1 0.4658 0.0042 (0.1066)2785.3 (1263.7) 2073.45 (9.227) 0.448 0.36%

60 2 0.6511 0.0031 (0.0782) 1847.3 (838.2) 1201.01 (5.345) 0.259 0.40%

1 0.7010 0.0093 (0.2362)2785.3 (1263.7) 3151.16 (14.023) 0.680 0.70%

The base shear coefficient and story rotation angle are ploted in figure 5.18. The data upto

test run 60 could only be plotted. Data for higher test run were not measured as the

instruments were romoved from the model. The model could have resisted story forces

more than the measured corresponding to test run, however, it is assumed that the maximu

resistance is observed during test run 60 on the basis of damage propogation. The cracks

144

developed during test run 30 were opened up and propagated in to the confining element and

sheared the mico-concrete.

0

0.5

1

0.0% 0.5% 1.0% 1.5%

Story Drit Rotation (%)

Bas

e Sh

ear

Coe

ffici

ent

Figure 5.18 Story resistance envelop

The first story rotation angle corresponding to significant cracks is 0.28 % and the

corresponding base shear coefficient is 0.447. It is worth mentioning that the model has been

tested untill the in-plane walls practically collapsed or severely damaged. The maximum

ground motion (PGA) recorded at this stage was 3.65 g. However, the ultimate limit states

could not be characterised by the experiemental resistance envolpe, available visual

information and experiemental resistance envelope of single story model of this research, and

test carried out on confined masonry buildings at other institutes could be utilised to define

the limit states.

The ratios of base shear coefficient (BSC) and first story rotation angle at maximum

resistance and ultimate state to damage limit state has been determined for different confined

masonry models and is summerized in table 5.11. The number of story and wall density ratio

of each model is also provided. It could be seen from the table that no specific coorelation

has been obtained in BSC and drift ratio and wall density or number of storires.

145

Table 5.11 Base shear and first story ratio at maximum and ultimate state

Model

Designation

No of

story

of model

building

Wall Density

ratio (%)

Maximum

Resistance/Damage Limit

Ultimate state/Damage

Limit

Reference

BSC

First Story

Drift,

Ф

BSCFirst Story Drift,

Ф (%)

M1/1d 2 3.5 1.38 5.2 0.6 10.37 Tomazevic, M., 2004

M1/1c 2 3.5 1 1 0.433 15 Tomazevic, M., 2004

M1 3 5.0 1.57 1.36 0.533 43 Tomazevic, M., 1996

M2 3 5.6 2.04 4.64 1.057 67.9 Tomazevic, M., 1996

M1 1 - 1.1 1.86 0.62 5.1 Alcocer, S.M., 2004

M3 3 4.1 1.1 1.85 0.91 6.73 Alcocer, S.M., 2004

Single story 1 5.64 1.53 4.72 1.06 6.28 This research

The scatter of the data of first story rotation angle at ultimate limit is large as it depends on

the structural system, type of materials used (fired clay brick, concrete block etc) and

structural configuration of the building used.

The following BSC and story drift ratios are expected at ultimate state for the double story

model studied in this research work:

Ratio of Base Shear Coefficient at Ulitmate and Damage limite state = 0.75

Ratio of First Story Drift at Ulitmate and Damage limite state = 5.5

The base shear coefficient and first story drift ratio at the ultimate state comes out to be 0.336

and 1.43 % respectively. A similar attempt has also been made by (Tomazevic, M., 2007) to

correlate the observed damage with displacement capacity and limit states. The ranges of

values for story rotation assigned to characteristic limit states are given as under:

Crack limit, Øcr = 0.2 % to 0.4 %,

Maximum Resistance, ØRmax = 0.3 % to 0.6 % and,

Limite state at collapse, Øcoll = 2.0 % to 4.0 %.

The base shear coefficient and story rotation angle for the three limit states for double story

model are given in table 5.12. The maximum ground acceleration (pga) measured during the

146

last test run was 3.65 g which resulted in the disintegation of ground floor in-plane walls.

However, in order to prevent the disintegraton of wall at the ultimate state, a lower value of

PGA is conisdered. The PGA measured at the late test run is reduced by 30%. The hysteretic

envelop is plotted in figure 5.18.

Table 5.12 Base shear and first story ratio at maximum and ultimate state

Description of limit state Base shear coefficient Story rotation angle

(%)

Maximum Ground

Acceleration (g)

Elastic Limit (R30) 0.448 0.26% 0.636

Maximum Resistance (R60) 0.680 0.70% 1.153

Ultimate State 0.336 1.43% 2.55

By comparing the values of rotation angle at the three limit states, it could be concluded that

experimentally obtained rotation angle at damage limit state is within the range assessed by

(Tomazevic, M., 2007). However, the rotation angle at ultimate state is less than the assessed,

the value is close to the upper bound at the maximum limit state.

0

0.2

0.4

0.6

0.8

0.00% 0.25% 0.50% 0.75% 1.00% 1.25% 1.50%


Bas

e Sh

ear

Coe

ffic

ient

Figure 5.19 Story resistance envelop

147

5.3.9 Response Modification Factor of Double Story Model

The base shear coefficient and story drift ratio has been idealized by bilinear curve as shown

in figure 5.19. 20% degradation from the maximum resistance limit is considered in the

idealization of the curve. The different parameters of the idealized curve are given below:

du = Ultimate displacement of the idealized bilinear curve = 0.36 inch (9.14 mm)

de = displacement at the elastic limit of the idealized bilinear curve = 0.11 inch (2.72 mm)

Global ductility ratio, µu = 3.4 and,

Response modification factor, R from equation 5.5 = 2.41

The response modification factor evaluated for double story building on the basis of global

ductility factor seems small as suggested by other authors. This could be partly because of

the reasons that full response upto collapse were not measured and maximum resistnace was

conservatively assumed at lower value. Secondly, the response accelerations corresponding

to displacement in channel # 9, considered for the evaluation of base shear, are small as

compared the maximum acceleration in each test run.

0

0.2

0.4

0.6

0.8

0.00% 0.25% 0.50% 0.75% 1.00% 1.25% 1.50%


Bas

e Sh

ear

Coe

ffic

ient

Figure 5.20 Hysteretic envelope and idealised bilinear relation

5.4 SEISMIC RESISTANCE OF PROTOTYPE BUILDING

The results obtained during shaking table test of the single and double story models are

extrapolated to prototype building by taking into consideration the laws of model similarity.


------- Idealised Curve

148

The maximum shake table motion during characteristics limit states should be converted to

maximum ground motion which would cause these limit state in the real building. Similarly,

the properties of model observed during the shaking table such as frequency and damping

during each test run, and base shear and drift at the three limit states should be scaled to the

prototype building.

However, properties of masonry materials and masses over each floor are adequately

simulated; the mechanical properties of masonry assemblage are not correctly modeled.

Actual relationship developed as a result of experimentally obtained properties of prototype

and model assemblage should be used to extrapolate model result to prototype.

As discussed earlier, shear was predominant mode of failure in both the models, scale factors

for each physical quantity is calculated as a result of scale factor corresponding to shear

strength. Table 5.13 gives the actual scale factors calculated keeping the geometric scale

factor of 4 and strength factor of 1.6. The scale factors for acceleration and time comes out to

be 0.4 and 3.16 respectively.

Table 5.13 Modeling scale factors to extrapolate model test results to prototype building

Physical Quantity Relationship Scale factor

True Model This Study

Length (L) SL = Lp/LM 4 4

Strength (f) Sf = fp/fm =SL 4 1.6

Strain (ε) Sε = εp/εm 1 1

Sp. Mass (γ) Sγ=γp/γM 1 1

Displacement (d) Sd = SL 4 4

Force (F) SF = SL2 Sf 64 25.6

Time (t) St = SL √(Sε Sγ/ Sf) 2 3.16

Frequency 1/ St 0.5 0.316

Velocity Sv = √(SεSf/ Sγ) 2 1.26

Acceleration Sf /(SL Sγ) 1 0.4

Table 5.14 and 5.15 give base shear and story drift corresponding to limit states of prototype

single and double story building respectively. The table also gives ground motion defined by

peak ground acceleration. The peak ground acceleration is determined by multiplying

149

maximum shake table acceleration with acceleration scale factor (0.4). The same acceleration

scale factor is used to convert the base shear force for model to prototype building.

Table 5.14 Parameters of seismic resistance for single story building


Coefficient

Story Rotation

angle (%)

Maximum Ground

Acceleration

(g)

Elastic limit (R125) 0.482 0.25 0.42

Maximum Resistance (R175) 0.778 1.18 0.81

Ultimate state (R150) 0.18 2.1 1.15

Table 5.15 Parameters of seismic resistance for double story building


Coefficient

Story Rotation

angle (%)

Maximum Ground

Acceleration

(g)

Elastic limit (R30) 0.180 0.37 0.254


Ultimate state 0.134 0.80 1.02

It could be seen from the tables that both single and double story models designed according

to Eurocode could be used in high seismic zones of Pakistan Building code 2007. Both the

models properly constructed and designed could resist strong earthquake. However, the

double story model because of its small wall area in the short direction of the ground floor

would significantly be damaged. Separation of walls from tie column and/or collapse of walls

would result as a consequence of strong earthquake.

5.5 COMPARING SINGLE AND DOUBLE STORY BUILDING

Single story building is comparatively more rigid than the double story building. The wall

density ratio of single story in the short direction (parallel to excitation) is 5.64 % as

compared to 3.87 % in the ground floor and 5.99 % in the second floor. This could be the

reason for the double story model that ground floor was more damaged than the first floor.

However, concentration of damage in the ground floor has also been observed by other

researchers. Damage limit state was observed at 0.42 g in the single story model, however

first significantly crack in the double story has been observed at 0.22 g.

150

However, significant degradation has been observed in single story model at the last test run,

the confining elements keep the walls from disintegration. At the last test run, separation of

walls and buckling of model rebars in the confining element were observed. The in-plane

walls in the ground floor of the double story on other hand disintegrated at the last test run.

The confining element could not prevent the walls disintegration at strong ground shaking.

The single story buildings are much stiffer. Designed according to Euro code, the single story

buildings could survive collapse at strong ground motion.

It is concluded that the double story building cracks at lower PGA value than the single story

building. As discussed earlier the walls disintegrated after their separation from tie columns.

It is recommended to provide horizontal reinforcement to connect the tie columns and

masonry walls at ground floor. As the first story is comparatively stiffer than the ground floor

and the damage is also small, the toothing would work to keep the integrity of masonry walls

and tie columns.

151

CHAPTER 6 CONCLUSION AND RECOMMENDATION

The objective of this research work was to determine the behavior of typical confined brick

masonry buildings subjected to seismic loadings. Response modification and ductility ratio of

the confined brick masonry building was evaluated. The research work was aimed at the

growing demand of confined brick masonry buildings after 2005 Kashmir earthquake which

resulted in the destruction of more than 450,000 buildings.

6.1 SUMMARY

A survey of building typology and inventory has been carried out in Peshawar city and

earthquake affected area, including Abbottabad and Mansehra city. About 65 building

drawings have been collected from these cities and analyzed. Typical single story and double

story buildings have been selected on the basis of wall density ratio close to mean value of

the analyzed drawings.

Masonry materials survey has also been made, including survey of mortar, bricks and rebars.

Masonry mortar samples were collected in Peshawar as well as in Abbottabad and Mansehra

city from the construction sites. The survey shows that cement-sand and cement-sand-khaka

(stone dust) mortar were the typical mortar used in the area. The popular mix proportions are

1:6, 1:8 in cement-sand and 1:4:4 in cement-sand-khaka by volume. The mean compressive

strength of masonry mortar was found to be 837 psi (5.77 MPa). Test data of fired clay brick

and rebars was collected from Material Testing Lab, N-W.F.P UET, Peshawar. Mean

compressive strength of the brick was 2350 psi (16.2 MPa). Grade 40 and 60 deformed bar

are mainly used in buildings. Grade 40 bars are mostly used in residential buildings from 3/8

to 6/8 inch diameter. Data about compressive strength of structural concrete was; however,

not collected. Compressive strength of concrete cores cut from existing buildings vary from

1500 (10.34 MPa) to 2500 psi (17.24 MPa). The mean compressive strength of masonry unit

and masonry mortar comply with minimum requirements of Pakistan building code 2007 and

Eurocode 6.

152

The experimental work has been divided into three phases. In the first phase properties of

prototype masonry have been determined. In the second phase, properties of model materials,

including masonry mortar, masonry unit and micro-concrete have been simulated. The

mechanical properties of model masonry have been evaluated. In the last and final phase

model buildings have been fabricated and tested on shake table to evaluate their seismic

response.

In order to fulfill the requirements of complete model similitude law extensive experimental

work has been carried out for modeling masonry mortar, model brick and micro concrete.

Mixes with different proportions have been prepared and tested in compression to simulate

the masonry mortar. Cement-sand, cement-sand-lime, cement-lime-surkhi (brick remains),

cement-lime-marble powder and lime-surkhi were used in different proportions. Almost 40

batches of masonry mortar have been tested. Finally, cement-lime-sand (1:1:5), has been

selected as masonry mortar. Cement-lime-sand (1:1:5), having coarser sand than used in

masonry mortar, has been selected as micro concrete. Cement-lime-surkhi (1:1:2) has been

used for fabricating model masonry unit. Surkhi (burnt brick remains) passed through sieve

no 8 and retained on sieve 30 has been used to simulate specific weight of the prototype brick

as cement-lime-sand resulted in high specific weight. In order to reduce the fabrication

efforts, model bricks were fabricated in three different dimensions. That is actual model brick

of dimensions 2.2x1.1x0.67 (56x27x17 mm) (length x width x height), model brick with

double height 2.2x1.1x1.34 inch (56x27x34 mm) and model brick double in width with

dimensions 2.2x2.2x0.67 (56x56x17 mm) are used in model masonry wallets.

The prototype and model masonry assemblage has been tested in compression, diagonal

compression and cyclic test. Modulus of elasticity and rigidity has been determined. The

compression strength of prototype masonry was 828 psi (5.7 MPa) and modulus of elasticity

was 290 psi (2.0 MPa). Diagonal shear strength of prototype masonry was 51.0 psi (0.35

MPa) and modulus of rigidity was 26.0 psi (0.18 MPa). Model masonry walls of all the three

type of bricks have been tested. It was concluded that model bricks doubled in height and

width resulted in high strengths than actual model brick walls.

153

A small scale model of single and double story building has been tested on single degree of

freedom shake table. Scale factor four and complete model similarity has been adopted for

the models construction on the basis of capacity of the shake table and economy.

Kobe accelerogram compressed in time with square root of scale factor but with the same

PGA value as original record has been used for shaking table test of the reduced model. The

models have been subjected to increasing intensity of vibration in each test run. The models

have been instrumented with accelerometers and displacement transducers connected at the

floor slab at front of the in-plane walls. Four accelerometers and four string pots have been

used in single story model. However, four string pots and two accelerometers have been

connected at each floor in double story models to measure response acceleration and

displacement at the floor level. Additional weights are attached to each floor of the model to

simulate the dead load of flooring. The confining elements (tie columns and bond beams) are

designed according to Eurocode requirements. However, horizontal reinforcement were not

provided to connect tie columns and masonry walls.

Both the models failed in shear. Cracks initiated in masonry walls were confined by the

confining elements. However, with the increased intensity of shaking, the cracks propagated

and damaged the tie columns. During the final intensity of shaking, crushing of masonry

units at the corners of walls, crushing of concrete and buckling of rebars in the tie columns

have been observed. In the case of double story building model, damage was concentrated in

the ground floor. However, the in-plane walls were severely damaged at high intensities of

shaking; the confining elements prevented the collapse of model. The confining elements

also prevented collapse of out-of-plane walls which are generally vulnerable in the URM

buildings. Separation of masonry walls from the tie columns at early stages of shaking could

be attributed to the absence of horizontal reinforcement. It is, therefore, recommended to

provide horizontal reinforcement to connect the tie columns and masonry walls. However,

further research work should be carried out to evaluate the effect of horizontal reinforcement

on the ductility and energy dissipation capacity of confined masonry walls. However, further

research work should be carried out to evaluate the effect of horizontal reinforcement on the

ductility and energy dissipation capacity of confined masonry walls.

154

Seismic resistance and deformation capacity of the model have been evaluated on the basis of

measured acceleration and displacement response. Base shear is determined by multiplying

the response acceleration, measured at the attainment of maximum response displacement

with masses concentrated at floor level. A graph of base shear coefficient, that is base shear

divided by total weight of the model and first story rotation angle, first story drift divided by

height of first story has been plotted. The curve is idealized as bilinear curve. Complete

elastic analysis has also been carried out by modeling the reduced scale building in SAP,

computer software. The response modification factor, R of single story model determined on

the basis of global ductility ratio is 3.04 and the ductility ratio, µ comes out to be 5.13 for

single story building. However, response modification factor determined by dividing elastic

base shear over ultimate base shear comes out to be 2.16 for the single story model. The

response modification factor evaluated for double story model on the basis of ductility ratio

is 2.41 which is conservative value.

In order to extrapolate the shaking table parameters and response characteristics of the model

to the prototype earthquake and building, laws of complete model similarity have been taken

into consideration. However, actual scale factor is to be considered instead of theoretical. The

actual scale factor is determined as the relation between properties of the prototype that are

target values to that of properties measured on model masonry. As the basic failure mode in

the single and double story model was shear, therefore shear strength should be kept as the

basis of the true scale factor. The scale factors for other physical quantities are determined on

the basis of geometric scale factor and the strength factor. The base shear and shake table

accelerations at the three characteristic states have been extrapolated to the prototype

building. The limit states are damage limit state where the first significant crack occurs or

where there is significant drop in the stiffness, the maximum resistance limit state and

ultimate limit state that is before collapse and where the structural walls in the first story are

severely damaged. Base shear and the acceleration at the three limit states are given in table

5.14 and 5.15. The tables are reproduced as given below.

155

Table 6.1 Parameters of Seismic Resistance for Single Story building


Coefficient

Story Rotation

angle (%)

Maximum Ground

Acceleration

(g)

Elastic limit (R125) 0.482 0.25 0.42


Ultimate state (R200) 0.18 2.1 1.15

Table 6.2 Parameters of Seismic Resistance for Double Story building


Coefficient

Story Rotation

angle (%)

Maximum Ground

Acceleration

(g)

Elastic limit (R30) 0.180 0.37 0.254


Ultimate state (R300) 0.134 0.80 1.02

It can be seen that both single and double story building would be able to resist with minor

damage an earthquake with PGA 0.40g and 0.25g and without collapse an earthquake with

PGA 1.1g and 1.0g respectively. It is concluded that properly constructed and designed

single and double story models could be used in high seismic zones (Pakistan Building Code

2007). On the basis of observed behavior and wall density ratio it could be concluded that the

Eurcode requirements are stringent for single story building.

6.2 CONCLUSIONS AND RECOMMENDATIONS

Based on the experimental work, the following conclusions and recommendations are made.

Further, research areas are identified to investigate vulnerability in the masonry buildings and

its subsequent mitigation.

Conclusions:

• Shear is the predominant failure mode in both single and double story models

• The analysis of measured response and observed behavior of the single story model reveals that the typical single story building would withstand with minor damage an earthquake of PGA 0.40g and would not collapse under an earthquake of PGA 1.15 g.

156

• The typical double story building would withstand with minor damage an earthquake of PGA 0.25g and without collapse an earthquake of PGA 1.0g.

• Single and double story confined masonry buildings properly designed and constructed could be used in high seismic zones (zone 3 and 4 of Pakistan Building Code 2007).

• The ground story walls could collapse or severely damaged during strong ground motion (that is PGA 0.8 and higher) because of the absence of horizontal reinforcement.

• The confining elements could prevent collapse of out-of-plane walls of both single and double story buildings at strong earthquake, if proper monolithic behavior of tie columns and masonry walls is achieved.

• The eurocode requirements for the design of confined masonry buildings seems stringent for single story building.

• The provision of toothing in walls could not prevent separation of walls from confining element at strong ground motion.

• The response modification factor of single story building confined according to Eurocode 8 is 3.0. Response modification factor for double story building designed according to Eurocode is determined to be 2.41. The Eurocode requirements for response modification factor are found adequate.

• The mean compressive strength of masonry unit, 2350 psi (16.2 MPa), tested in the Material Laboratory, N-W.F.P UET, Peshawar, comply with the minimum requirements of Pakistan Building Code 2007 and Eurocode 6.

• The mean compressive strength of masonry mortar collected from field in Peshawar, Abbotabad and Mansehra after Kashmir earthquake comply with the minimum requirements of Pakistan Building Code 2007 and Eurocode 6.

Recommendations:

• In order to delay extensive damage to masonry wall, it is recommended to provide horizontal bed joint reinforcement to connect the masonry walls and tie-columns.

• Wall density ratio should not be less than 5 % in seismic zone 3 and 4.

• The building should be regular in plan and elevation.

157

• Minimum thickness of masonry wall should be kept at 9 inch (229 mm).

• Minimum thickness of confining element should be 9 inch (229 mm).

• Minimum 1% longitudinal reinforcement should be provided in the confining element.

• Stirrups of 3/8 inch (10 mm) diameter bars should be provided in the confining elements at a maximum spacing of 6 inch (152 mm) c/c.

• At least 48 diameters splice length should be provided.

• The longitudinal reinforcement of tie-columns should be adequately anchored in foundation and bond beam/floor slab. The reinforcement must be tied with foundation reinforcement at the bottom as well as with the bond beam/floor slab reinforcement at the top.

• Tie-column should be provided at 16 ft (4.2 m) c/c horizontal spacing.

• Not more than two stories building should be constructed in zone 4 and three stories in zone 3.

• Minimum compressive strength of brick, mortar and concrete should be1800 psi (12.4 MPa) , 800 psi (5.5 MPa) and 2000 psi (13.8 MPa), respectively.

6.3 FUTURE RESEARCH WORK

• Numerical analysis of the typical confined brick masonry buildings is recommended.

• As real earthquake is three dimensional phenomenons, experimental testing of typical confined brick masonry building model on 6-degree of freedom shake table is recommended.

• Cyclic testing of full-scale confined brick masonry walls with different dimensions of confining elements and reinforced with different reinforcement ratio should be carried out. The optimum dimensions of confining element and reinforcement ratio could be suggested and made part of the Pakistan Building Code 2007.

• Shake table test of single story building model with smaller dimensions and less reinforcement ratio as required by Eurocode for both horizontal and vertical confining element should be tested and compared with the results of this research.

158

• Effect of different earthquake accelerograms on the typical confined masonry building should be carried out.

• Confined masonry walls with different horizontal reinforcement ratio should be carried out and the effect of horizontal reinforcement on the seismic resistance and ductility should be investigated in future studies.

• Shake table testing of typical confined masonry building with flexible diaphragm should be carried out to study its behavior.

• The study of seismic behavior of typical confined block masonry buildings is recommended for future research work.

159

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165

APPENDIX A: LIST OF EQUIPMENT

A1.0 Dynamic Test

A 1.1 Dytran Accelerometers

Model 3191A

Weight = 775 grams

Sensitivity = 10.0 V/g

Maximum range = ±2g

Frequency Range = 0.1 to 1000 Hz

A 1.2 Dytran Model 3056B3 Accelerometers

Weight = 10 grams

Sensitivity = 500 mV/g

Acceleration range = ±10g

Frequency Range = 0.1 to 10,000 Hz

A 1.3 Celesco String pots

PT1DC Series

Maximum Range 0-20 inch,

Accuracy = 0.15 %

A2.0 Static Material Test

Shimadzu Universal Testing Machine (UTM), UH-200

Load Capacity = 200 t

Loading speed = 0-50 mm/min

A3.0 Straining Frame (Static Cyclic)

A3.1 Kyowa Loading Cell

Load Capacity = 50 t (2 Nos)

Load Capacity = 25 t (2 Nos)

Macros Hyraulic Power Supply (HPS)

A3.2 Data Acquisition Sytem

Kyowa UCAM 70 Data Logger

166

Maximum Channels = 30+30 (strain gages+dispacement gages ports)

Maximum Frequency = 20 Hrz/Channel

167

APPENDIX B: DESCRIPTION OF EARTHQUAKE

SIMULATOR

The earthquake simulator (shake table) used in this study is horizontal single degree of

freedom vibration facility driven by a servo-hydraulic actuator. The shake table is anchored

to the reinforced concrete foundation with dimensions of 20 x 20 x 5 ft (6 x 6 x 1.5 m) in the

Earthquake Engineering Center (EEC), N-W.F.P University of Engineering and Technology.

The actuator is connected to the backstop and aluminum table top via ball joint assemblies.

These bass joints allow a small amount of transverse and rotational adjustment flexibility for

alignment.

Following are the capabilities and characteristics of the shake table:

• Table size 5 ft x 5 ft (1.5 x 1.5 m) aluminum table top with M14 tapped holes on 7-7/8 inch (20 cm) both directions,

• Uni-axial horizontal motion,

• A total of 8 linear roller bearings on 4 linear rails to guide table motion and prevent vertical, side to side, roll, and yaw motion,

• Peak to peak displacement is 10 inch (25.4 cm),

• Peak velocity (with 4000 kg test specimen) is 43.3 inch/see (1.1 m/s ),

• Peak acceleration (with a 4000 kg test specimen) is 1.1 g,

• Maximum test item weight; 8000 kg. Test items above 4000 kg leads to significant system performance degredation,

• frequency range is 0.15 to 50 Hrz

• Maximum test item eccentricity is 10.0 ton-m

Data Acquisition and Control Characteristics

The data acquisition and control system for the shake table is a Data Physics SignalStar

Vector Vibration Controller operating on a Dell desktop computer. The system allows for a

feedback accelerometer on the moving table, a PC-based digital control system reading this

168

acceleration, and the same PC system producing an analog drive signal to the actuator servo

controller. The Data Physics provides a total of 16 channels for table accelerometers, for

response measurements of specimen etc)

Hydraulic System:

The hydraulic actuator is supplied by Gardner Systems. The actuator has a 13 inch (33.0 cm)

stroke with 1.0 inch (25.0 cm) of cushion and 15 mm of bumper/hard stop. The actuator is

rated at 11 kips (5 metric tons) and includes three-two stage Moog G761-3005 servo valves

rated at 15 GPM (56.8 LPM), Delta P compensation, and a magnetostrictive Balluf

displacement transducer to measure actuator displacement.

Shake table system is supplied with 5 GMP hydraulic pump with 3 micron filtering and water

cooling. The system has 40 gallon reservoir. The system is supplied with two accumulators.

These are identical 10 gallon 3000 psi bladder accumulators to provide for peak flow

capacity during high velocity seismic events.

169

APPENDIX C: MEASURED RESPONSE HISTORIES

C.1 Acceleration Time Histories: Single Story Model

Time [sec]

3029.52928.52827.52726.52625.52524.52423.52322.52221.52120.52019.51918.51817.51716.51615.51514.51413.51312.51211.51110.510

Acc

eler

atio

n [g

]

0.1

0.05

0

-0.05

-0.1

Figure C1 Acceleration during test run R05 in channel 00

Time [sec]

3029.52928.52827.52726.52625.52524.52423.52322.52221.52120.52019.51918.51817.51716.51615.51514.51413.51312.51211.51110.510

Acc

eler

atio

n [g

]

0.1

0.05

0

-0.05

-0.1

Figure C2 Acceleration during test run R05 in channel 01

Time [sec]

3029.52928.52827.52726.52625.52524.52423.52322.52221.52120.52019.51918.51817.51716.51615.51514.51413.51312.51211.51110.510

Acc

eler

atio

n [g

]

0.1

0.05

0

-0.05

-0.1

Figure C 3 Acceleration during test run R05 in channel 02

Time [sec]

3029.52928.52827.52726.52625.52524.52423.52322.52221.52120.52019.51918.51817.51716.51615.51514.51413.51312.51211.51110.510

Acc

eler

atio

n [g

]

0.1

0.05

0

-0.05

-0.1


Time [sec]

3029.52928.52827.52726.52625.52524.52423.52322.52221.52120.52019.51918.51817.51716.51615.51514.51413.51312.51211.51110.510

Acc

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atio

n [g

]

0.1

0.05

0

-0.05

-0.1


170

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.53

Acc

eler

atio

n [g

] 0.1

0.05

0

-0.05

-0.1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.53

Acc

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atio

n [g

] 0.1

0.05

0

-0.05

-0.1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.53

Acc

eler

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n [g

] 0.1

0.05

0

-0.05

-0.1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.53

Acc

eler

atio

n [g

] 0.1

0.05

0

-0.05

-0.1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.53

Acc

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atio

n [g

] 0.1

0.05

0

-0.05

-0.1


171

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

] 0.150.1

0.050

-0.05-0.1

-0.15


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.20.150.1

0.050

-0.05-0.1

-0.15-0.2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.20.150.1

0.050

-0.05-0.1

-0.15-0.2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.20.150.1

0.050

-0.05-0.1

-0.15-0.2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.20.150.1

0.050

-0.05-0.1

-0.15-0.2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

] 0.4

0.2

0

-0.2

-0.4


172

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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atio

n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.6

0.4

0.20

-0.2

-0.4

-0.6


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.6

0.4

0.20

-0.2

-0.4

-0.6


173

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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atio

n [g

]

0.6

0.4

0.20

-0.2

-0.4

-0.6


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.6

0.4

0.20

-0.2

-0.4

-0.6


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

eler

atio

n [g

]

0.6

0.4

0.20

-0.2

-0.4

-0.6


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

] 0.4

0.2

0

-0.2

-0.4


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 0.4

0.2

0

-0.2

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174

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 0.4

0.2

0

-0.2

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Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 0.4

0.2

0

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Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

1

0.5

0

-0.5

-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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1

0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 1

0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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-1


175

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 1

0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 1

0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

] 1

0.5

0

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-1


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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] 1

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0

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-1


176

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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atio

n [g

]

21.5

10.5

0-0.5

-1-1.5

-2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

21.5

10.5

0-0.5

-1-1.5

-2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

21.5

10.5

0-0.5

-1-1.5

-2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

21.5

10.5

0-0.5

-1-1.5

-2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

21.5

10.5

0-0.5

-1-1.5

-2


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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3

2

1

0

-1

-2

-3


177

Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

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]

3

2

1

0

-1

-2

-3


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

]

3

2

1

0

-1

-2

-3


Time [sec]

2019.51918.51817.51716.51615.51514.51413.51312.51211.51110.5109.598.587.576.565.554.543.532.521.510.50

Acc

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n [g

] 4

2

0

-2

-4


C.2 Displacement Time History:

Time [sec]

4038363432302826242220181614121086420

Dis

plac

emen

t (in

)

0.20.150.1

0.050

-0.05-0.1

-0.15-0.2

Figure C 51 Displacement during test run R05 in channel 07

Time [sec]

4038363432302826242220181614121086420

Dis

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t (in

)

0.20.150.1

0.050

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178

Time [sec]

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t (in

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Time [sec]

4038363432302826242220181614121086420

Dis

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t (in

)

0.30.250.2

0.150.1

0.050

-0.05


Time [sec]

4038363432302826242220181614121086420

Dis

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t (in

)

0.20.150.1

0.050

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Time [sec]

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Time [sec]

4038363432302826242220181614121086420

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179

Time [sec]

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Time [sec]

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180

Time [sec]

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) 0.4

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) 0.4

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Time [sec]

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181

Time [sec]4038363432302826242220181614121086420

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0.5

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Time [sec]4038363432302826242220181614121086420

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Time [sec]4038363432302826242220181614121086420

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1

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Time [sec]

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1

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Time [sec]

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Time [sec]

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182

Time [sec]

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1

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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)

1.51

0.50

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Time [sec]

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Dis

plac

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t (in

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0.50

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183

Time [sec]

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Dis

plac

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)

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Time [sec]

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Time [sec]

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Dis

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0.50

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Time [sec]

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Dis

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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Dis

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Time [sec]

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Dis

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2

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185

Time [sec]

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Dis

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2

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Time [sec]

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Time [sec]

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Dis

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Time [sec]

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Time [sec]

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Time [sec]

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C.3 Acceleration Time History: Double Story Model


Time [sec]

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Acce

lera

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[g]

0.1

0.05

0

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Time [sec]

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[g]

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0

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Time [sec]

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Acce

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tion

[g]

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0.05

0

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Time [sec]

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tion

[g]

0.1

0.05

0

-0.05

-0.1


Time [sec]

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tion

[g]

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0.1

0

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187

Time [sec]

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tion

[g]

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0.1

0

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Time [sec]

4038363432302826242220181614121086420

Acce

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tion

[g]

0.2

0.1

0

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Time [sec]

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Acce

lera

tion

[g]

0.2

0.1

0

-0.1

-0.2


Time [sec]

4038363432302826242220181614121086420

Acce

lera

tion

[g]

0.2

0.1

0

-0.1

-0.2


Time [sec]

4038363432302826242220181614121086420

Acce

lera

tion

[g] 0.4

0.2

0

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Time [sec]

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188

Time [sec]

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[g]

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0.4

0.20

-0.2

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-0.6


Time [sec]

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0.2

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Time [sec]

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Time [sec]

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[g] 0.5

0

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Time [sec]

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Time [sec]

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Time [sec]

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Time [sec]

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C.3 Displacement Time History: Double Story Model

Time [sec]

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[g] 0.05

0

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Time [sec]

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0.05

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Time [sec]

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0.1

0.05

0

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Time [sec]

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0.05

0

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Time [sec]

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0

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191

Time [sec]

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0

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Time [sec]

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tion

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0.1

0.05

0

-0.05

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Time [sec]

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lera

tion

[g]

0.1

0.05

0

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Time [sec]

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lera

tion

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0.1

0.05

0

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Time [sec]

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0.1

0.05

0

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Time [sec]

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192

Time [sec]

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Time [sec]

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0.1

0

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Time [sec]

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0.1

0

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Time [sec]

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0.1

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Time [sec]

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0.1

0

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Time [sec]

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193

Time [sec]

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Time [sec]

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0.1

0

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Time [sec]

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0.1

0

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Time [sec]

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[g]

0.30.20.1

0-0.1-0.2-0.3


Time [sec]

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[g]

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Time [sec]

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194

Time [sec]

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[g]

0.30.20.1

0-0.1-0.2-0.3


Time [sec]

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lera

tion

[g]

0.30.20.1

0-0.1-0.2-0.3


Time [sec]

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Acce

lera

tion

[g]

0.30.20.1

0-0.1-0.2-0.3


Time [sec]

4038363432302826242220181614121086420

Acce

lera

tion

[g]

0.30.20.1

0-0.1-0.2-0.3


Time [sec]

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tion

[g] 0.2

0

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Time [sec]

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0

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195

Time [sec]

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0

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Time [sec]

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0

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Time [sec]

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0

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Time [sec]

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[g] 0.5

0

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Time [sec]

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[g] 0.5

0

-0.5


Time [sec]

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0.60.40.2

0-0.2-0.4-0.6-0.8


196

Time [sec]

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Acce

lera

tion

[g]

0.60.40.2

0-0.2-0.4-0.6


Time [sec]

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tion

[g] 0.5

0

-0.5


Time [sec]

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[g] 0.5

0

-0.5


Time [sec]

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Time [sec]

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197

APPENDIX-D: SCHEMATIC DIAGRAMS SHOWING

DAMAGE PROPAGATION DURING DIFFERENT TEST RUN. D.1 Single Story Model

Figure D1 Hairline cracks in wall 12 before start of test

Figure D2 Crack propagation in wall 1 during test run R60

198



199



200



201


Figure D10 Crack propagation in wall A during test run R80

202

Figure D11 Crack propagation in wall C during test run R80

Figure D12 Crack propagation in wall F during test run R80

203

Figure D13 Crack propagation in wall A during test run R175

Figure D14 Crack propagation in wall C during test run R175

204

Figure D15 Crack propagation in wall F during test run R175

205

D.2 Double Story Model

Figure D16 Hairline cracks before start of test in wall A

Figure D17 Hairline cracks before start of test in wall H

206

Figure D18 Hairline cracks before start of test in wall 1

Figure D19 Crack propagation in wall 1 during test run R30 (Pga = 0.636g)

207

Figure D20 Crack propagation in wall 9 during test run R30 (Pga = 0.636g)

Figure D21 Crack propagation in wall 9 during last test run (Pga = 3.65g)

208

Figure D22 Crack propagation in wall F during test run R20 (Pga = 0.33g)

Figure D23 Crack propagation in wall A during test run R20 (Pga = 0.33g)

209

Figure D24 Crack propagation in wall H during test run R30 (Pga = 0.56g)

Figure D25 Crack propagation in wall A during test run R30 (Pga = 0.56g)

210

Figure D26 Crack propagation in wall H during last test run (Pga = 3.65g)

Figure D27 Crack propagation in wall A during last test run (Pga = 3.65g)

211

APPENDIX E: ELASTIC ANALYSIS OF SINGLE AND

DOUBLE STORY MODEL BY SAP

The elastic analysis of single and double story model has been carried out by modeling

building in SAP2000, computer software. The confining beams and columns are modeled as

frame element and masonry walls are modeled as shell element of SAP2000.

E-1.0 Material Properties:

E-1.1 Masonry

Modulus of Elasticity = 46.28 ksi,

Weight per unit volume = 95.3 pcf,

E-1.2 Micro Concrete

Compression Strength = 367 psi

Modulus of Elasticity = 1092 psi

Weight per unit volume = 98.8 pcf,

E-1.3 Frame Sections

Tie Column-1 (C6x9) = 1.5 x 2.25 inch

Tie Column-2 (C9x9) = 2.25x2.25 inch

Bond Beam (B6x0) = 1.5x2.25 inch

Slab (S5) = 1.25 inch

Wall (W9) = 2.25 inch

Time History Function

212

Figure E 1 Time History Function

Figure E 2 Single Story Model in SAP

213

Figure E 3 Double Story Model in SAP

E-2.0 Results:

E-2.1 Maximum Displacement:

Maximum Top Displacement in single story model = 0.4 mm

Maximum Top Displacement in Double Story Model = 3.17 mm

Maximum Ground Floor Displacement in Double Story Model = 2.47 mm

E-2.1 First Natural Frequency:

Single Story Model = 0.0266 Hrz

Double Story Model = 0.0535 Hrz

214

VITA

Amjad Naseer was born in Lakki Marwat, N-W.F.P, Pakistan, on May 12, 1972. He

graduated from Department of Civil Engineering, N-W.F.P University of Engineering and

Technology, Peshawar in 1995 with a degree in civil engineering. Amjad Naseer completed

his M.Sc degree in Structural Engineering from the same institution. Following the 2005

Kashmir earthquake, Amjad Naseer started work on the evaluation of typical confined brick

masonry buildings in his Ph.D studies. He completed his Ph.D degree in 2009, which was

funded by Higher Education Commission of Pakistan under the Indigenous 5000 scholarship

scheme, batch-I.

Documents

Performance Behavior of Confined Brick Masonry …prr.hec.gov.pk/jspui/bitstream/123456789/550/1/358S.pdfHorizontal bed joint reinforcement is recommended to connect the tie columns