iii THE STRUCTURAL PERFORMANCE OF PRECAST WITH … · 2016. 8. 3. · Structural Wall Elements 2.11.1 Plain Concrete Wall 31 2.11.2 Reinforced Concrete Wall 32 2.11.3 Response of

iii

THE STRUCTURAL PERFORMANCE OF PRECAST

LIGHTWEIGHT FOAMED CONCRETE PANEL (PLFP)

WITH DOUBLE SHEAR CONNECTORS

SURYANI BINTI SAMSUDDIN

A thesis submitted in

fulfilment of the requirements for the award

Degree of Master in Civil Engineering

Faculty of Civil and Environmental Engineering

UniversitiTunHusseinOnnMalaysia

AUGUST 2015

vii

ABSTRACT

Traditional cast in situ construction has been a common practice adopted by

building industry in this country. This process could not meet the huge demand on

affordable housing which is the major issue now because it requires large number of

workers, massive casting and erection work, and longer construction time. As a

solution to this, a precast system needs to be innovated as an alternative to this

traditional system. Current research has been focusing on precast panel system made

of conventional concrete. Therefore, this research investigated the structural

behaviour of single and two connected Sandwiched Precast Foamed Concrete Panel

(PLFP). Eight single PLFP and three sets of connected PLFP panels were cast using

foamed concrete as the wythe and polystyrene as the core layer. The panels were

strengthened with steel bar reinforcement embedded in both wythes which were

connected to each other by the steel shear truss connectors. Single PLFP panels were

tested under axial load while connected PLFP panels were tested under flexural load

test. The results were analyzed in term of the panel’s ultimate load, crack pattern

and mode of failure, load-deflection and load-strain profiles. It was found that the

ultimate load recorded in single PLFP panels from experiment showed good

agreement with the values from previous research. Connected PLFP panels were

able to sustain slightly lower ultimate load compared to single PLFP panel. The

percentage difference between these ultimate load values is about 14%. The value of

ultimate load recorded for single and connected PLFP panels were 171 kN and 147

kN, respectively. For both single and connected PLFP panels, it was observed that

ultimate load, crack pattern and failure mode, load-deflection and load-strain profiles

were significantly influenced by the panel’s slenderness ratio. Finite element

analysis using LUSAS software is also carried out to study the effect of slenderness

ratio on ultimate load. It was observed that the difference value between FEM and

Experimental for single and connected PLFP panels are in a good agreement which

recorded 4.5% and 5.8%, respectively.

viii

ABSTRAK

Cara pembinaan yang menggunakan kaedah tradisional tuang di situ telah

menjadi amalan biasa yang diamalkan oleh industri pembinaan di negara ini. Proses

ini tidak dapat memenuhi permintaan yang besar terhadap rumah mampu milik yang

merupakan masalah besar sekarang kerana ia memerlukan sejumlah besar pekerja,

pemutus yang besar dan kerja pembinaan, dan masa pembinaan yang lebih lama.

Sebagai penyelesaian untuk ini, sistem pratuang perlu lebih inovasi sebagai alternatif

kepada sistem tradisional ini. Penyelidikan semasa telah memberi tumpuan kepada

Sistem Panel Pratuang yang diperbuat daripada konkrit konvensional. Oleh itu,

kajian ini akan menyiasat kelakuan struktur pratuang tunggal yang disambungkan

dengan dua Panel Lapisan Konkrit Ringan Pratuang Berbusa (PLFP). Lapan panel

tunggal PLFP dan tiga set panel PLFP bersambung dibancuh menggunakan konkrit

berbusa sebagai lapisan dan polistirena sebagai lapisan teras. Panel ini diperkuat

dengan tetulang bar keluli yang tertanam dalam kedua-dua lapisan yang

disambungkan antara satu sama lain dengan penyambung kekuda keluli ricih. Panel

PLFP tunggal dan bersambung telah diuji menggunakan ujian beban paksi dan ujian

beban lenturan empat titik. Hasilnya dianalisis dari segi beban muktamad panel,

corak keretakan dan bentuk kegagalan, beban-pesongan dan profil beban-terikan.

Didapati bahawa beban muktamad yang dicatatkan pada panel PLFP tunggal dari

eksperimen ini menunjukkan hubungan yang baik dengan nilai-nilai dari

penyelidikan sebelumnya. Panel PLFP bersambung mampu menampung beban

muktamad yang lebih rendah sedikit berbanding dengan panel PLFP tunggal.

Peratusan perbezaan di antara kedua-dua nilai beban muktamad ialah sebanyak 14%.

Nilai beban muktamad yang dicatatkan untuk panel PLFP tunggal dan panel PLFP

bersambung masing-masing ialah 171kN dan 147kN. Untuk kedua-dua panel PLFP

tunggal dan disambung, diperhatikan bahawa beban muktamad, corak keretakan dan

kegagalan mod, beban-pesongan dan beban-terikan profil itu sedikit banyak

dipengaruhiolehnisbah kelangsinganpanel. Analisis unsur terhingga menggunakan

ix

perisian LUSAS dijalankan bagi menentukan pengaruh nisbah kelangsingan ke atas

beban muktamad. Dapat diperhatikan bahawa nilai perbezaan antar FEM dan ujikaji

untuk panel PLFP tunggal dan panel PLFP bersambung berada dalam anggaran yang

baik yang mana masing-masing mencatatkan 4.5% dan 5.8%.

x

CONTENTS

TITLE PAGE

THESIS TITLE iii

DECLARATION iv

DEDICATION v

ACKNOWLEDGEMENT vi

ABSTRACT vii

ABSTRAK viii

CONTENTS x

LIST OF TABLES xviii

LIST OF FIGURES xxii

LIST OF ABBREVIATION xxvii

CHAPTER 1 INTRODUCTION 1

1.1 Introduction 1

1.2 Problem Statement 3

1.3 Objectives of Research 4

1.4 Scope of Research 4

1.5 Important and Contribution of Research 5

1.6 Organisation of Thesis 6

xi

CHAPTER 2 LITERATURE REVIEW 8

2.1 Precast Concrete Sandwich Panel (PCSP) 8

2.2 Material Properties on Sandwich Panel 10

2.2.1 Core Layer 10

2.2.2 Shear Connector and Reinforcement 13

2.3 Structural Behaviour of Sandwich Panel 15

2.3.1 Insulation Type 16

2.3.2 Slenderness Ratio 16

2.3.3 Effect of Shear Connector 18

2.4 Precast Lightweight Foamed Concrete 20

Sandwich Panel.

2.5 Advantage of Sandwich Panels 23

2.6 Foamed Concrete Fabrication 24

2.7 Process of Manufacturing Foamed Concrete 26

2.8 Properties of Foamed Concrete 26

2.9 Application of Foamed Concrete 28

2.10 Type of Sandwich Panel 29

2.10.1 Non-Composite Panel 30

2.10.2 Fully-Composite Panel 30

2.10.3 Partially-Composite Panel 30

2.11 Precast Concrete Sandwich Panel as 31

Structural Wall Elements

2.11.1 Plain Concrete Wall 31

2.11.2 Reinforced Concrete Wall 32

2.11.3 Response of Precast Concrete 33

Sandwich Panel Subjected to Axial

Load

2.11.4 Precast Lightweight Foamed 34

Concrete Sandwich Panel (PLFP)

with Single Shear Connector

Subjected to Axial Loading

2.11.5 Solid Reinforced Concrete Wall 34

under Pure Axial Loads

2.12 Precast Concrete Connection 35

xii

2.12.1 Introduction 35

2.12.2 Connections between Precast 36

Concrete Sandwich Panels

2.13 Wall to Wall Connection 38

2.14 Finite Element Analysis 40

2.14.1 Introduction 40

2.14.2 Type of Finite Element Analysis 41

2.14.2.1 One-Dimensional Element 41

2.14.2.2 Two-Dimensional Element 42

2.14.2.3 Three-Dimensional Element 42

2.14.3 Material Non-Linearity 43

2.15 Previous Research of Finite Element 43

Method (FEM)

2.16 Summary 47

CHAPTER 3 METHODOLOGY 49

3.1 Introduction 49

3.2 Experimental Investigation on PLFP Panel 51

3.2.1 Designation and Dimension of 51

Single PLFP Panel under Axial

Load Test

3.2.2 Designation and Dimension of 52

Connected PLFP Panel under

Flexural Load Test

3.2.2.1 Wall to Wall Connection 53

3.3 Materials Preparation and Fabrication 56

of PLFP Specimens

3.3.1 Material Preparation of Foamed 56

Concrete

i) Cement 56

ii) Fine Aggregates 57

iii) Foam Agent 57

3.3.2 Material for Producing PLFP 57

xiii

i) Wythe 58

ii) Core Layer 59

iii) Normal Concrete Capping 59

iv) Reinforcement 60

v) Shear Connectors 60

3.3.3 Procedure of Casting the Panels 61

3.4 Testing of Material 66

(Cubes and Cylinder of Foamed Concrete)

3.4.1 Cube Test 66

3.4.2 Split Tensile Test 67

3.4.3 Young’s Modulus 68

3.5 Test of PLFP Panel under Axial Load 70

3.6 Four Point Load Test on Two Connected 74

3.7 Validation using Finite Element Method 75

3.8 Material Model for Finite Element Analysis 76

3.8.1 Constitutive Models 76

3.8.1.1 Concrete Model 77

3.8.1.2 Von Mises Model 78

3.9 Analysis of Results 78

CHAPTER 4 EXPERIMENTAL RESULTS 80

4.1 Introduction 80

4.2 Objectives of Experimental Work 82

4.3 Experimental Results and Analysis 82

4.3.1 Material Properties of 82

Foamed Concrete

4.3.2 Tested PLFP Panel under 84

Axial Load

4.3.2.1 Ultimate Load 84

4.3.2.2 Crack Pattern and 85

Failure Mode

4.3.2.3 Load-Deflection Profile 89

xiv

4.3.2.4 Strain Distribution on the 91

Concrete Surface

4.3.3 Two PLFP Panels with L-Bar 93

Vertical Connection Tested under

Flexure Load


4.3.3.2 Crack Pattern and Mode 94

of Failure

4.3.3.3 Load-Horizontal Deflection 97

Profiles

4.3.3.4 Load-Strain Relationship 98

4.3.4 Effect of Slenderness Ratio on 101

Panel’s Structural Behaviour


4.3.4.2 Crack Pattern and 102

Failure Load

4.3.4.3 Load-Deflection Profile 103

4.3.4.4 Load-Strain Distribution 104

4.4 Comparison of the Load Bearing Capacity, 105

Pu, from Experiment withThe Pu values

from Classical Formulae and Previous

Research

4.5 Comparison Between Structural 107

Performances of Single PLFP Panel with

Two Panel PLFP Panels Connected using

Vertical Connection

4.5.1 Ultimate Load 108

4.5.2 Crack Pattern and Mode of Failure 109

4.5.3 Load-Deflection Profile 110

4.5.4 Load-Strain Profile 111

4.6 Summary 112

xv

CHAPTER 5 FINITE ELEMENT METHOD 113

5.1 Introduction 113

5.2 Objective 114

5.3 Modelling of PLFP Panel 114

5.3.1 Physical Model 114

5.3.2 Material Model 116

5.3.2.1 Concrete Wythe 117

5.3.2.2 Steel Reinforcement and 119

Shear Connector

5.3.2.3 Concrete Capping 120

5.3.2.4 Loading & Analysis Control 121

5.4 PLFP Panel Subjected to Axial Load 123

5.4.1 Ultimate Load of PLFP Panel 123

Under Axial Load

5.4.2 Validation of Experimental Results 125

5.4.3 Comparison Result of Ultimate 125

Load from FEM and Experiment

5.4.4 Comparison Result of Load 126

Deflection From FEM and

Experimental for PLFP PA-5

5.4.5 Effect of Slenderness Ratio on 127

Ultimate Load

5.5 Connected PLFP Panel Subjected to 128

Flexural Load

5.6 Summary 129

CHAPTER 6 CONCLUSION 130

6.1 Conclusion 130

6.1.1 To Determine the Structural 130

Behavior of Single PLFP Panel

with Various Slenderness Ratios

Subjected to Axial Load.

6.1.2 To Determine the Structural 131

xvi

Behaviour of Two PLFP Panels

with L-Bar Vertical Connection

Subjected to Flexural Load.

6.1.3 To Compare the Ultimate Load 132

Obtained from Experiment with the

Values Obtained from Classical

Formulae and Previous Research.

6.2 Recommendations 132

REFERENCES 133

APPENDIX 139

Appendix A : Foamed Concrete

Table A1 : Result of Dry Density for PLFP 139

after 7, 14 and 28 Days

Table A2 : Compressive Strength at 7, 14 139

and 28 Days for PLFP Panel

Table A3 :Tensile Strength of Foamed 140

Concrete for PLFP Panel at 28-Days

Table A4 : Modulus Young, E for PLFP Panel 141

A5 : Data for Panel PA 1 (S1) 142

A6 : Data for Panel PA 2 (S2) 144

Appendix B : Strain Distribution 146

Table B : Maximum Surface Strain values from 146

Experiment

Appendix C : Reinforcement Bar Properties 147

xvii

Table C :Tensile Strength of Reinforcement Bar 147

Figure C1 : Tension Testing Result for 3 mm 148

Diameter Reinforcement







Appendix D : Load Strain Graph for PLFP 150

Panel

Appendix E : 154

Table E : Data for Deflection of PLFP Panel 154

Appendix F 162

Table F : Data for Surface Strain Readings 162

of PLFP Panel

Appendix G 170

Table G : Data for Surface Strain of PLFP Panel 170

Appendix H 171

Table H :Comparison of Load Bearing Capacity 171

by using Previous Formulae and Classical

Formulae

Appendix I 175

Calculation of Loading for 3 storey Residential 175

Building

xviii

LIST OF TABLES

TABLE TITLE PAGE

1.1 Density Classification of Concrete Aggregates 2

(Mindess and Young, 1981)

2.1 Typical Mixture Details for Foamed Concrete 11

(BCA, 1994)

2.2 Typical Properties for Foamed Concrete (BCA, 1994) 11

2.3 Experimental Results for Horizontal Bending Test 12

(Kabir, 2005)

2.4 Ultimate Load and Deflection at Mid-High in 14

Panels Specimens (Mohammed & Nasim, 2009)

2.5 Crack and Failure Loads for Panel Specimens 17

(Benayouneet al., 2006)

2.6 Typical Foamed Concrete Mixes 25

(Newman & Choo, 2003)

2.7 Typical Properties of Foamed Concrete 27

(Cement Concrete Institute 2010)

2.8 Comparison of Load Capacity for Imperfect Walls 45

with Different Wall Height (Bagaber, 2007)

3.1 Dimension and Details of Specimens for Axial 52

Load Test

3.2 Dimension and Details of Specimens for Four 53

Point Load Test

3.3 Foam Concrete Ratio 58

4.1 Dimension and Properties of PLFP Panel Specimens 81

xix

4.2 Dimension and Properties of PLFP Connected using 81

L-Bar Vertical Connection

4.3 Compressive Strength at 7, 14 and 28 days for Panel 83

PA-1 to PA-8

4.4 Tensile Strength of Panel PA-1 to PA-8 at 28-Days 83

4.5 Young’s Modulus, E, for Panel PA 1 to PA 8 84

4.6 Ultimate Failure Load for PLFP Panels 85

4.7 Crack Pattern and Mode of Failure for PLFP Panels 86

4.8 Maximum Surface Strain 93

4.9 Ultimate Failure Loads of PLFP Panels 94

4.10 Crack pattern for panels PC-1, PC-2 and PC-3 94

4.11 Deflection Value of PLFP Panels 103

4.12 Ultimate Loads of PLFP Panels from Experiment, 105

Empirical Formulae and Previous Researchers.

4.13 The Difference Percentage of Load bearing Capacity 107

for PLFP PA-5

4.14 First Crack and Ultimate Load For Single and 108

Two Connected PA-1

4.15 Crack Pattern and Failure Mode for Panels PA-1 109

and PC-3

5.1 Dimension and Properties of PLFP Panels for FEM 115

Modelling

5.2 Properties of Foamed Concrete used in the PLFP FEM 117

Model

5.3 Plastic Properties of Foamed Concrete Wythes 118

5.4 Properties of Steel used as Reinforcement and 120

Shear Connectors

5.5 Properties of Normal Concrete used in the PLFP 121

FEM Model

5.6 Load Bearing Capacity for PLFP Panel 125

5.7 Ultimate Load of PLFP from Experiment and FEM 126

5.8 Ultimate Load of Connected PLFP from Experiment 128

and FEM

xx

A1 Result of Dry Density for PLFP after 7, 14 and 28 Days 141

After Exposed to Air

A2 Compressive Strength at 7, 14 and 28 Days for Panel 141

PA 1 to PA 8

A3 Tensile Strength of Foamed Concrete for Panel PA 1 to 142

PA 8 at 28 Days

A4 Modulus Young, E, for Panel PA 1 to PA 8 143

A5 Sample Calculation for Modulus Young for Panel PA 1 144

A6 Sample Calculation for Modulus Young for Panel PA 2 146

B1 Maximum Surface Strain Values from Experiment 148

D1 Data for Deflection of PLFP Panel PA 1 153








E1 Data for Surface Strain Readings of PLFP Panel PA 1 161








F Surface Strain Distribution of PLFP Panel 169

G1 Comparison of Load Bearing Capacity by using Previous 170

Formulae and Classical Formulae for PA 1






xxi










xxii

LIST OF FIGURES

FIGURE TITLE PAGE

2.1 Types of Sandwich Construction (An, 2004) 9

2.2 Shotcrete Lightweight Sandwich Panel (Kabir, 2005) 13

2.3 Schematic for the Test Setup for Four-Point Bend Test 14

with Strain Gauge Location (Mohammed &Nasim, 2009)

2.4 Schematic Diagrams for the Panels used in the 15

Experimental Work (Mohammed &Nasim, 2009)

2.5 Comparison between AAC and FRP/AAC Shear ` 15

Strengths (Mohammed &Nasim, 2009)

2.6 Typical Precast Concrete with Truss Shaped 21

Shear Connector(Benayouneet al., 2006)

2.7 Precast Concrete Sandwich Panel 22

(Mohamad and Muhammad, 2011)

2.8 Manufacturing Process of Foamed Concrete (Ying, 2007) 27

2.9 Precast Concrete Sandwich Panel 28

(Losch, 2005)

2.10 Twenty-Storey Mutual Benefit Life, Philadelphia, 29

Pennsylvania (PCI Commitee, 1997)

2.11 Window Wall Panels Serve as Elements of Vierendeel 29

Truss on One Hundred Washington Square Office

Building, Minneapolis, Minnesota (PCI Commitee, 1997)

2.12 Types of Precast Concrete Sandwich Panels 30

(PCI Committee, 1997)

xxiii

2.13 Typical Reinforcement Details (Jackson, 1995) 37

2.14 Mechanical Connection 38

2.15 Top View of Wall to Wall Connection 39

(Rossley et al., 2014)

2.16 Front View of Wall to Wall Connection 40

(Rossley et al., 2014)

2.17 1-Dimensional Elements (Guntor, 2011) 41

2.18 Applied of 1-Dimensional Element (Guntor, 2011) 42

2.19 2-Dimensional Elements (Guntor, 2011). 42

2.20 3-Dimensional Elements (Guntor, 2011). 43

2.21 Loading and Boundary Condition (Vaghei et al., 2006) 46

3.1 Flow Chart of the Methodology 50

3.2 Schematic Diagram for Single PLFP Panel 54

3.3 Details of Reinforcement in 2 PLFP Panels and Its 55

Connection

3.4 Plan View of Reinforcement Orientation in L-Bar 55

Connections

3.5 Ordinary Portland Cement 56

3.6 Foam Generator 57

3.7 Sample of Foam 57

3.8 Foamed Concrete Wythe in PLFP 58

3.9 Polystyrene Core Layer 59

3.10 Reinforcement and Shear Connectors 60

3.11 Arrangement of Double Shear Truss Connectors in PLFP 61

3.12 Double Shear Truss Connectors for 90mm Thick PLFP 61

Panel

3.13 (a) The First Step is to Place the First Layer of Foamed 62

Concrete Wythe

3.13 (b) The Second Step is to Place the Insulation Layer 62

(Polystyrene)

3.13 (c) The Third Step is to Place the Second Layer of 63

Foamed Concrete Wythe

3.14 (a) Concrete Poured into the Formwork for the 1st Layer 63

as the Bottom Wythe

xxiv

3.14 (b) The BRC, Shear Connectors Truss and Polystyrene were 63

Placed Horizontally on the Top of the Lower Wythe

3.14 (c) Foamed Concrete Poured on the Top of Polystyrene 64

Layeras the Upper Wythe

3.14 (d) Finish of the PLFP Panel Specimen 64

3.15 The First Step is to put the Panel Side by Side and 65

Tight Tight Together with 30 mm Gap

3.16 The Second Step is to Place the Foamed Concrete 65

into the Connection

3.17 Cube Specimens 66

3.18 Compressive Strength Testing Machine 67

3.19 Specimen Positioned in a Testing Machine for 68

Determination of Splitting Tensile Strength

3.20 Test specimens placing at Universal Testing 70

Machine with attachment of Compressmeter

3.21 Experimental Set-Up of Wall Panel Clamped to 71

Reaction Frame.

3.22 Experimental Set-Up using Magnus Frame 72

3.23 Arrangement of Strain Gauges and LVDT 73

3.24 Testing Setup under Four Point Bending Test 74

3.25 The Arrangement of LVDT in Connected Wall for 75

HorizontalDisplacement Measurement

3.26 Simplified Failure Envelope for Biaxial Concrete 77

Model(LUSAS, 2000)

3.27 Von Mises Failure Theory 78

4.1 Ultimate Strength versus Compressive Strength for 85

PLFP Panels

4.2 Crack and Crush at the Bottom Half of Panel PA-1 87

4.3 Crack and Crush at the Top half of Panel PA-2 87

4.4 Crack and Crush at the Bottom Part of the Panel PA-3 88

4.5 Crack and Crush at the Middle Part of Panel PA-4 88

4.6 Crack and Crush at the Top Half of the Panel PA-7 88

4.7 Load-Horizontal Deflection Profiles at Mid-Height 90

of Panels

xxv

4.8 Load Strain Curves for Panel PA-2, PA-5 and PA- 6 92

under Axial Load

4.9 Crack and Crush on the Diagonal Angle Approximately 95

45o at the Top of Panel PC-2 and PC-3

4.10 Crack Occurred in PC-2 and PC-3 96

4.11 LVDT Position 96

4.12 (a) Load-Deflection Profile for Panel PC-3 97

4.12 (b) Load-Deflection Profile for Panel PA-3 across the Width 98

4.13 Strain Gauge Position 99

4.14 Load- Strain Profile at the Top and Bottom of the 99

Connection for PC-3

4.15 Load-Strain Profile at the Connection for PC-3 100

4.16 Load-Strain Profile at the Centre of the PLFP Panel 100

for PC-3

4.17 Ultimate Strength, Pu, versus Slenderness Ratio, h/t 102

PA-1 to PA-8

4.18 Slenderness Ratio versus Maximum Deflection of 104

PLFP Panels

4.19 Comparison of Ultimate Load vs Slenderness Ratio 106

as obtained from Experiment, Codes and Previous

Research

4.20 (a) Crack and crush at Bottom Part of Panel PA-1 109

4.20 (b) Crack and Crush on the Diagonal Angle Approximately 109

45oat the Top of Panel PC-3

4.21 Load Deflection Profile Profile for PA-1 and PC-3 110

4.22 Load-Strain Profile at the Top, Middle and Bottom 111

Part of PA-1

5.1 2-D Plane-Stress Element Model of PLFP 116

5.2 Attributes of foamed concrete plastic properties as in 119

FEM

5.3 PLFP Support and Loading Condition 122

5.4 Deflection of Wythes in PA-5 124

5.5 Difference of Ultimate Load between Experimental and 126

FEM

xxvi

5.6 Comparison of Load-Deflection between Experimental 127

and FEM value for PA-5

5.7 Model of Connected PLFP Panel under Flexural 128

Load Test

Appendix C Load Strain Graphs for PLFP Panels 149

xxvii

LIST OF ABBREVIATION

2D – Two Dimensional

3D – Three Dimensional

AAC – Autoclaved Aerated Concrete

ACI – American Concrete Institute Code

ASTM – American Standard Testing Method

BRC – Bar Reinforcement

BS – British Standard

CFRP – Carbon Fibre-Reinforced Polymer

CIDB – Construction Industry Development Board of Malaysia

E – Modulus Young

EPS – Expanded Polystyrene Insulation

FE – Finite Element

FEA – Finite Element Anaysis

FEM – Finite element method

FRP – Fiber Reinforced Polymer

GFRP – Glass Fibre-Reinforced Polymer

IBS – Industrialised Building System

LUSAS – London University Structural Analysis Software

LVDT – Linear Voltage Displacement Transducer

PCSP – Pre-Cast Concrete Sandwich Panel

PLFP – Precast Lightweight Foamed Concrete Sandwich Panel

SG – Strain Gauge

UTHM – Universiti Tun Hussein Onn Malaysia

XPS – Extruded Polystyrene Insulation

1

CHAPTER 1

INTRODUCTION

1.1 Introduction

Construction material such as brick, timber, concrete and steels are increasing in

demand due to rapid expansion of construction activities for housing and other

buildings. For structure which is constructed by using conventional concrete, its

self weight represents a very large proportion of the total load on the structure.

Furthermore, it uses aggregate which is one of earth’s natural resources. With

these two reasons, there is a need for alternative system to fulfill the construction

demand in term of its strength, affordability and environmental friendly. For

structure which is constructed by using conventional concrete, its self weight

represents a very large proportion of the total load on the structure. The strength

and other properties of concrete are dependent on how its ingredients are

proportioned and mixed. It depends on the usage of a good quality concrete,

which can be defined as having a workable fresh concrete and unlikely to

segregate.

Lightweight concrete can be defined as a type of concrete which includes

an expanding agent in that it increases the volume of the mixture while giving

additional qualities such as self compactibility and lighter weight (Zakaria, 1978).

2

It is lighter than the conventional concrete with a dry density of 300 kg/m3 up to

1840 kg/m3 which is 23% to 87%lighter. It was first introduced by the Romans in

the second century (Sarmidi, 1997).

One of the main properties that are associated with the lightweight concrete is

its low density. Lower in density leads to reduction in weight and this means

reduction in the total load. Foamed concrete is one of the lightweight concrete and is

classified as cellular concrete. It has a uniform distribution of air voids throughout

the paste or mortar. Scanlon (1998) stated that lightweight concrete is a concrete that

have a low density concrete compared to the normal concrete. Table 1.1 shows the

density classification of the concrete aggregates.

Table 1.1: Density Classification of Concrete (Mindess and Young, 1981)

Category Unit Weight of

Concrete (kg/m3)

Unit Weight of Dry-Rodded Aggregates

(kg/m3)

Typical Concrete Strengths

(Mpa)

Typical Application

Ultra Lightweight

300 – 1100 < 500 < 7 Nonstructural

insulating material

Lightweight 1100 – 1600 500 – 800 7 – 14 Masonry Units Structural

Lightweight 1450 – 1900 650 – 1100 17 – 35 Structural

Normal Weight 2100 – 2550 1100 – 1750 20 – 40 Structural

Heavy Weight 2900 – 6100 >2100 20 – 40 Radiation Shielding

Lightweight foamed concrete is suitable for both precast and cast-in-place

applications. Good strength characteristics with reduced weight make lightweight

foamed concrete suitable for structural and semi-structural applications such as

lightweight partitions, wall and floor panels and lightweight block concrete. This

structure has become more popular in recent years because it offers more advantages

compared to the conventional concrete (Mindess and Young, 1981).

In the precast wall load bearing structures, there are panel to panel

connections such as wall-floor, wall-foundation, wall-roof and wall-wall connection.

Panel to panel connection can be categorized as horizontal connection and vertical

3

connection. Horizontal connections are the wall-floor and wall-roof connection

while vertical connection is the connection between wall panels that are side by side

in the same floor. Jointing system between these walls constitutes an essential link

in the lateral load-resisting systems, and their performance influence the pattern and

distribution of lateral forces among the vertical elements of a structure. The

connections between panels are extremely important since it influences both the

speed of erection and the overall integrity of the structure.

1.2 Problem Statement

The development of lightweight, industrialized and sustainable housing system in

Malaysia as per modular coordination system is a need of the day. In Malaysia,

brickwall is a common wall for use as load bearing wall. However, brickwall is time

consuming, require large number of workers, difficult to control the quality and

produce high wastage percentage at the construction site. Therefore an alternative

precast system is required to replace this traditional system. To encounter demands

from the growing population and migration of people to urban areas, new alternative

technology is required in the construction industries which can meet demands for

higher performance, affordable quality housing and environmental efficient. Current

research on precast wall panel only focuses on the performance of solid panel from

conventional concrete. These panels are strong but have a weakness such as heavy

and not environmental friendly.

Dolan and Foschi (1989) stated that connections are an important part of

every structure not only from the point of view of structural behavior, but also

related to the cost of production. Connections play a key role in dissipation of

energy and redistribution of loads. With a strong connection between wall panels, a

structure will have strength of stability to prevent structure failure.

Thus, as a solution, this research investigated the Precast Lightweight

Foamed Concrete Panel (PLFP) with double shear connectors as an alternative to

fulfill the rapid housing demand in Malaysia. As a part of this effort, an

investigation to develop a vertical connection for PLFP panels with foamed concrete

fill was also undertaken. .

4

1.3 Objectives of Research

The objectives of the study are:

i. To determine the structural behavior of single PLFP panel with various

slenderness ratios subjected to axial load.

ii. To determine the structural behaviour of two PLFP panels with L-bar vertical

connection subjected to flexural load.

iii. To compare the ultimate load obtained from experiment with the values

obtained from classical formulae and previous research.

The aforementioned structural behaviour refers to ultimate load, failure mode and

crack pattern, load-deflection profile and strain distribution on the concrete’s surface.

1.4 Scope of Research

This research investigated the structural performance of the Precast Lightweight

Foamed Concrete Panel (PLFP), as a single wall tested under axial load and two (2)

vertically connected walls tested under flexural load. In this study, PLFP was

designed to have a compressive strength of 12 MPa and strengthened with double

shear connectors. The experimental programme in this study was categorized into

two phases. Phase 1 was material tests to determine the material properties of

foamed concrete. This included its compressive strength, tensile strength and

modulus of elasticity. Phase 2 was an experimental programme which includes eight

(8) panel specimens tested under axial load and three (3) sets of two single PLFP

panels connected using vertical connection tested under flexural load test. The

panels were cast and fabricated using foamed concrete as its outer layers and

extended polystyrene as its insulation or core layer. It was strengthened by

embedding reinforcement bars in the skin layers which were connected to each other

by double shear truss connectors.

5

Various height and thickness of PLFP panels were used to study the influence

of slenderness ratio on the structural behavior of single PLFP panels. The results for

axial load test on single PLFP panel were validated using finite element method.

Two single PLFP panels were connected using vertical connection with L-bar

reinforcement. The material used as the infill for the connection is foamed concrete

with density of 1700 kg/m2 to 1800 kg/m2.

The results for single PLFP panels tested under axial load and two PLFP

panels connected and tested under flexural load were studied in terms of its load

carrying capacity, crack pattern and mode of failure, load-deflection profiles, and

strain distribution on foamed concrete surface. The results of this experiment were

validated using the Finite Element Method and formula from previous researcher.

1.5 Importance and Contribution of Research

The main aim of this research is to investigate the structural behaviour of PLFP as a

load bearing wall. Lightweight sandwich panel is of interest in this study since it has

higher strength to weight ratio compared to solid precast made of conventional

concrete. At the same time it will contribute to green building by producing a

cleaner and neater environment at project site, controlled quality, and a lower total

construction time and costs.

Single PLFP panel with various slenderness ratio and two PLFP connected

panels vertically were tested under axial and flexure load, respectively. Findings

from this research will encourage the use of the new approach to produce lightweight

composite wall elements for industrialized building system and hence promoting

better quality construction and innovative system in our construction industry.

PLFP system with double shear connectors studied in this research is

expected to achieve the intended strength for use in low to medium rise building.

Considering its lightweight and precast construction method, it is feasible to be

developed further as a competitive IBS building system. The result from this

research could be used as a guideline for those who are interested to develop a PLFP

panel as a walling unit in the industry and its future development as a structural

element.

6

1.6 Organisation of Thesis

This thesis consists of six (6) chapters. The summary of each chapter is described

below:

Chapter 1

This chapter presents the introduction of lightweight foamed concrete material and

its properties to be used as precast wall panel as a substitute for conservative in-situ

construction. It also presents the objectives and scope of research as well as the

importance and contribution of research.

Chapter 2

Chapter 2 presents the literature review from previous research on the structural

performance of precast panel from various materials and design. Review on the

connection between panels is also discussed. This chapter also covers the discussion

on classical equations for panel’s ultimate load from the codes and previous research.

Chapter 3

This chapter describes the methodology of this research. It includes the material tests

to determine foamed concrete’s material properties, axial load test for single PLFP

panel and four point bending load test for double PLFP panels vertically connected

to study its structural behavior. The foamed concrete’s material properties will be

used in finite element method to validate the experimental results. The fabrication of

PLFP panels and its connection will also be described.

7

Chapter 4

This chapter presents the results form material test, axial load test and four point

bending load test. The result of validation using previous researcher and empirical

formulae also presented in this chapter. The observed panel’s structural behavior is

discussed in terms of its ultimate strength, crack pattern and mode of failure, load-

deflection profiles, and load-strain profiles for both single and two connected PLFP

panels.

Chapter 5

This chapter presents the Finite Element Method, FEM, of PLFP panel which

include the modeling and simulation process on single PLFP panel subjected to axial

load and two PLFP connected panels tested under flexural load. The results obtained

from FEM will be used as the validation of experimental results.

Chapter 6

This chapter presents the conclusion on the findings of the PLFP panel’s structural

behavior as obtained from the experiment and recommendations for future research.

8

CHAPTER 2

LITERATURE REVIEW

2.1 Precast Concrete Sandwich Panel (PCSP)

Precast concrete can be defined as a concrete member that is cast in a plant. The

precast wall panel is one of the precast concrete structure that purposely constructed

to speed up the wall making construction and to reduce the dependencies of the

skilled worker as well as to reduce the construction waste and cost. Precast concrete

sandwich panels are a layered structural system composed of a low-density core

material bonded to, and acting integrally with relatively thin, high strength facing

materials.

Recent development of precast concrete has encouraged studies on various

lightweight materials such as structural wall panel systems. This system comply

with the IBS concepts, which enable cost saving, energy efficient and quality

improvement. A typical building element in a precast building system is precast wall

panel. The difference between precast concrete wall and precast concrete sandwich

panel is the presence of insulation layer (Aziz, 2002).

The development of a usage of sandwich panel is increasing within the past

few years because manufacturers are looking for new and viable product. Precast

concrete wall panels are often used as the exterior cladding of buildings and may

also serve as bearing walls or shear walls. Precast concrete sandwich wall panels are

9

used as exterior and interior walls for many types of structures. The main benefit of

using the sandwich structure concept in structural components is its high bending

stiffness and high strength to weight ratios (Belouttar et al., 2008). The sandwich

structure may readily be attached to any type of structural frame, for instance,

structural steel, reinforced concrete, pre-engineered metal and precast or prestressed

concrete.

Precast concrete sandwich panel normally consists of two layers of high

strength skins or wythe and are separated by a lower strength core layer. The wythes

are relatively thin while the core is relatively thick but lighter in weight. The

common materials used for wythes are steel, aluminium, timber, fiber reinforced

plastic or concrete while the materials used for the cores are balsa wood, rubber,

solid plastic material or polyethylene, rigid foam material (polyurethane,

polystyrene, phenolic foam), or from honeycombs of metal or paper (Benayoune et

al., 2006). Figure 2.1 presents a few types of sandwich panel elements (An, 2004).

Such sandwich structures have gained widespread acceptance within the aerospace,

naval/marine, automotive and general transportation industries as an excellent way to

obtain extremely lightweight components and structures with very high bending

stiffness, high strength and high buckling resistance (Mahfuz et al., 2004; Liang and

Chen, 2006).

(a) Foam Core Sandwich

(b) Honeycomb Core Sandwich

(c) Web Core Sandwich

(d) Truss Core Sandwich

Figure 2.1: Types of Sandwich Construction (An, 2004)

10

Sandwich panel have gained much attention by the researcher because of its

effectiveness as a structural element in engineering field. In the building and

construction industries, most of the researches published on sandwich panel are

related to the study of load bearing non-composite type of PCSP (Jokela et al., 1981,

Olin et al., 1984, Hopp et al., 1986 and Bush, 1994). Section 2.2 will discuss about

the previous research related to the sandwich panel studies.

2.2 Material Properties on Sandwich Panel

The chosen of material for the core and wythe in the sandwich panel is really

important. The material of core and wythe is one of the factor that determine the

strength of the sandwich panel. The wythes of sandwich panels are generally made

of thin, high strength sheets material. The structural requirements for wythe

materials are their abilities to resist local loads and resistance to corrosion and fire.

The core materials are generally thicker and made of lower dense materials. The

core is low in density because the core usually does not take any load and function as

an insulation material. Various types of materials therefore provide various

structural behaviours of the sandwich panels.

2.2.1. Core Layer

Foamed concrete is seen as lightweight material that is suitable for use in sandwich

panel because of its advantages. Cement foams are preferably used as core materials

for sandwich structures in building construction because they have low thermal

activity and good fire resistance. Kunhanandan et. al., (2007) stated that foam

concrete is a lightweight material consisting of Portland cement paste or cement

filler matrix (mortar) with homogeneous void or pore structure created by

introducing air in the form of small bubbles. Introduction of pore is achieved

through preformed foaming agent (mixing of water and aerated to form foam before

being added to mixture) and mix foaming (foaming agent mixed with the matrix).

11

According to British Cement Association (BCA, 1994), compressive strength

of foamed concrete depends on the density, initial water / cement ratio and cement

content. Density of foamed concrete has an influence on its ultimate strength.

Foamed concrete with density below 600 kg/m3 usually consists of cement, foam

and water. Higher densities foamed concrete are produced by adding fine sand.

Ordinary Portland cement is used as the binder in foamed concrete. Cement contents

for the most commonly used mixtures are between 300 kg/m3 and 375 kg/m3.

Typical mixture details and properties of foamed concrete are given in Table 2.1 and

Table 2.2 below:

Table 2.1: Typical mixture details for foamed concrete (BCA, 1994)

Table 2.2: Typical Properties of Foamed Concrete (BCA, 1994)

Dry Density

(kg/m3) Compressive

Strength(N/mm2) Thermal

Conductivity (W/mK)

Modulus of Elasticity (kN/mm2)

Drying Shrinkage (%)

400 0.5-1.0 0.10 0.8-1.0 0.30-0.35

600 1.0-1.5 0.11 1.0-1.5 0.22-0.25

800 1.5-2.0 0.17-0.23 2.0-2.5 0.20-0.22

1000 2.5-3.0 0.23-0.30 2.5-3.0 0.18-0.15

1200 4.5-5.5 0.38-0.42 3.5-4.0 0.11-0.09

1400 6.0-8.0 0.50-0.55 5.0-6.0 0.09-0.07

1600 7.5-10.0 0.62-0.66 10.0-12.0 0.07-0.06

Wet Density (kg/m3) 500 900 1300 1700

Dry Density (kg/m3) 360 760 1180 1550

Cement (kg/m3) 300 320 360 400

Sand (kg/m3) 420 780 1130

Base Mix W/C ratio Between 0.5 and 0.6

Air Content (%) 78 62 45 28

12

Ramli (2008) studied the use of ferrocement sandwich panel for

industrialised building system. Experimental investigation was conducted to

evaluate the structural performance of the ferrocement sandwich panel. This

included the load-deflection characteristics, crack resistance, and moment curvature

of the ferrocement elements when exposed to air and salt water curing. The results

showed that continuous salt water curing made significant improvement on the

flexural behaviour of panel by increasing its ultimate load carrying capacity, and

reducing its crack width and deflection.

Kabir (2005) investigated the structural performance of shotcrete lightweight

sandwich panel with compressive strength of 12 MPa and tensile strength of 1.2 MPa

under shear and bearing loads. The sandwich panel consisted of shotcrete wythes

which enclose the polystyrene core. Three specimens are provided for horizontal

bending tests, each sandwich panel is 300 cm long and 100 cm wide, the upper and

lower concrete wythes are 6 and 4 cm thick, respectively. It was reinforced by the

diagonal 3.5 mm cross steel wires welded to the 2.5 mm steel fabric embedded in

each wythe as shown in Figure 2.2. Tests for flexural and direct shear loading were

carried out based on ASTM E-72 and ASTM 564, respectively. From the

experiment result, it was found that the crack propagates to the upper layer, at 1200

kg load. The bottom mesh was yielded and the crushing of concrete causes the

instability of the panel. The maximum load was recorded at 2200 kg. Table 2.3

shows the ultimate loads and their corresponding displacement of slabs for the

horizontal flexural load test.

Table 2.3: Experimental Results for Horizontal Bending Test. (Kabir, 2005)

Specimen No

Thickness (cm)

Type of Shotcrete

Cement Content

�� (Kg) Max. Deflection

(mm)

Slab-1 Slab-2 Slab-3

16 16 16

Manual Manual Manual

300 kg/m³ 300 kg/m³ 300 kg/m³

2200 1900 1800

80 40 80

Figure 2.2: Shotcrete Lightweight Sandwich Panel

2.2.2 Shear Connector and Reinforcement

Pantelides et al., (2003), tested nine precast concrete wall assemblies with CFRP

connectors. Variations in shear area and surface preparation were investigated. Test

results showed that failure of the CFRP composite connection was nonductile,

similar to that of the steel connection but at three times the lateral load resisted by

the steel connection.

be highly dependent on the geometry and stiffness of the connection.

Mohammed and Nasim (2009) st

sandwich panel which composed of Fiber Reinforced Polymer (FRP) as the wythe

and Autoclaved Aerated Concrete (AAC) as the core.

shown in Figure 2.3

different AAC wrapping systems

bidirectional FRP lamina. Figure 2.4 shows the

on both strength and ductility of panels.

ultimate load and maximum deflection at mid

2.5 shows the comparison between AAC and FRP/AAC shear strength.

bidirectional FRP wrapping is shown to provide more ductility and toughness

compared to the panels with unidirectional FRP wrapping

: Shotcrete Lightweight Sandwich Panel (Kabir, 2005)

Shear Connector and Reinforcement


Variations in shear area and surface preparation were investigated. Test


that of the steel connection but at three times the lateral load resisted by

the steel connection. The development length of the CFRP composite was found to


Mohammed and Nasim (2009) studied the structural behavior of lightweight


and Autoclaved Aerated Concrete (AAC) as the core. Four-point bending tests as

3 were carried out on half scaled panel specimens with two

different AAC wrapping systems, namely unidirectional FRP lamina and

rectional FRP lamina. Figure 2.4 shows the significant influence of FRP lamina

on both strength and ductility of panels. Table 2.4 shows the results

ultimate load and maximum deflection at mid-height of the panel specimens. Figure

shows the comparison between AAC and FRP/AAC shear strength.


o the panels with unidirectional FRP wrapping (Plain AAC)

13

(Kabir, 2005)


Variations in shear area and surface preparation were investigated. Test


that of the steel connection but at three times the lateral load resisted by

The development length of the CFRP composite was found to


udied the structural behavior of lightweight


point bending tests as

nel specimens with two

namely unidirectional FRP lamina and

significant influence of FRP lamina

4 shows the results which give the

the panel specimens. Figure

shows the comparison between AAC and FRP/AAC shear strength. Panels with


(Plain AAC).

Table 2.4: Ultimate Loa

Panel No Dimension

UFFS

BFFS1

BFFS2

BFFS3

1200×175×100

1200×175×100

1200×175×100

1200×175×100

Figure 2.3: Schematic

Strain Gauge Location

Figure 2.4: Schematic D

: Ultimate Load and Deflection at Mid-High in Panels (Mohammed and Nasim, 2009)

Dimension (mm)

Reinforcement Type

Ultimate Load (KN)

1200×175×100

1200×175×100

1200×175×100

1200×175×100

Unidirectional

Bidirectional

Bidirectional

Bidirectional

15.54

13.56

14.14

16.24

: Schematic diagram for the Test Setup for Four-Point Bending Test with Strain Gauge Location (Mohammed and Nasim, 2009)

4: Schematic Diagrams for the Panels used in the Experimental (Mohammed and Nasim, 2009)

14

anels Specimens

Load (KN)

Final Mid-Deflection

(mm)

11.97

33

25.40

28.24

Point Bending Test with (Mohammed and Nasim, 2009)

xperimental Work

Figure 2.5: Comparison between AAC and FRP/AAC Shear S

As discussed above, the choice of materials used in sandwich panels have

significant influence on its mechanical properties.

2.3 Structural Behaviour of Sandwich Panel

The complex behaviour of

uncertain role of the shear connectors and the interaction between its various

components has led researchers to rely on experimental investigations backed by

simple analytical studies.

important type of construction is due to the high cost of full scale testing and the

extreme difficulty of fabricating small

factors that affected the structural behaviour of the panels

slenderness ratio of the panel and the effect of connector.

5: Comparison between AAC and FRP/AAC Shear S(Mohammed and Nasim, 2009)


significant influence on its mechanical properties.

Structural Behaviour of Sandwich Panel

The complex behaviour of sandwich panel is due to its material non



simple analytical studies. The scarcity of information on the behaviour of this


extreme difficulty of fabricating small-scale specimens. This part were discussed the

factors that affected the structural behaviour of the panels such as insulation type,

slenderness ratio of the panel and the effect of connector.

15

5: Comparison between AAC and FRP/AAC Shear Strengths


due to its material non-linearity, the



n the behaviour of this


This part were discussed the

such as insulation type,

16

2.3.1 Insulation Type

Frankl et al. (2011) investigated six precast, prestressed concrete sandwich

wall panels which were designed and tested to evaluate their flexural response under

combined vertical and lateral loads. The study included panels fabricated with two

different insulation types: expanded polystyrene (EPS) insulation and extruded

polystyrene (XPS) insulation. According to the manufacturer, the selected EPS

insulation had a nominal density of 16 kg/m3 and a nominal compressive strength of

90 kPa. The selected XPS insulation had a nominal density of 29 kg/m3 and a

nominal compressive strength of 170 kPa. The panels were 6.1 m x 3.7 m, 200 mm

thick and consisted of three layers. The flexural behaviors of six full-scale insulated

precast, prestressed concrete sandwich wall panels were investigated. The panels

were subjected to monotonic axial and reverse-cyclic lateral loading to simulate

gravity and wind pressure loads, respectively. Based on the findings of this study,

two conclusions were made as listed below:

i. Panel’s stiffness and deflections are significantly affected by the type and

configuration of the shear transfer mechanism. Panel’s stiffness is also

affected by the type of foam used.

ii. For a given shear transfer mechanism, a higher percent composite action can

be achieved using EPS insulation rather than XPS insulation.

2.3.2 Slenderness Ratio

Benayoune et al. (2006) studied the behaviour of pre-cast reinforced sandwich wall

panels under the influence of axial load. Six full-scaled specimens with various

slenderness ratios, H/t, were tested. All specimens were made of square welded mild

steel BRC mesh of 6 mm diameter with 200 x 200 mm and diagonal truss connectors

bent at 45 degrees used to tie the inner and outer concrete wythe.

The test results were analysed in the context of axial load bearing capacity,

load-deformation profiles, slenderness ratio, cracking pattern and mode of failure.

From this study, it was found out that the first cracks were recorded to appear at

loads of 44 to 79 percent of the ultimate loads as shown in Table 2.

the strength of panels decreased nonlinearly with the increase in the slenderness

ratio.

Table 2.

From the results

The linear strain distribution across the panel’s thickness reflected certain degree of

composite behaviour.

in a fully composite manner.

the behaviour of wall panels with various types and sizes of shear connectors.

Lian (1999) carried out a test

concrete sandwich panel under axial and eccentric loads.

and tested. The panels were 1.5m long, 0.75m wide and 40

i.e. 40 mm thick concrete wythes with a 50 mm

load capacity for pure axial loaded panels was computed using expressions

applicable to solid walls could not be directly applied to sandwich panel.

it may also be noted that the slenderness ratio,

the load bearing capacity of axial loaded panels

Oberlender (197

varying from 8 to 28, aspect ratios (H/L) from 1 to 3.5 and thicknesses equal to 75

mm with hinged top and

loads of 44 to 79 percent of the ultimate loads as shown in Table 2.


Table 2.5: Crack and Failure Loads for Panel Specimens(Benayoune et al., 2006)

results, it shows that both concrete wythes were

linear strain distribution across the panel’s thickness reflected certain degree of

composite behaviour. However, the study could not be concluded that the panels act

in a fully composite manner. Further experimental works are required to understand


Lian (1999) carried out a test program to study the behaviour of reinforced

concrete sandwich panel under axial and eccentric loads. Four specimens were cast

The panels were 1.5m long, 0.75m wide and 40-50-40 mm construction,

i.e. 40 mm thick concrete wythes with a 50 mm thick insulating layer.

for pure axial loaded panels was computed using expressions

applicable to solid walls could not be directly applied to sandwich panel.

ted that the slenderness ratio, H/t is an important factor influencing

the load bearing capacity of axial loaded panels.

Oberlender (1977) tested 54 wall panels with slenderness ratios (H/t


mm with hinged top and bottom edges under uniformly distributed axial and

17

loads of 44 to 79 percent of the ultimate loads as shown in Table 2.5. It shows that


: Crack and Failure Loads for Panel Specimens

were deflected together.

linear strain distribution across the panel’s thickness reflected certain degree of

However, the study could not be concluded that the panels act

Further experimental works are required to understand


program to study the behaviour of reinforced

Four specimens were cast

40 mm construction,

thick insulating layer. The ultimate

for pure axial loaded panels was computed using expressions

applicable to solid walls could not be directly applied to sandwich panel. However,

important factor influencing

) tested 54 wall panels with slenderness ratios (H/tw)


bottom edges under uniformly distributed axial and

18

eccentric loadings. The eccentricity was applied at 1/6 of the wall thickness. The

reinforcement was disposed in double layers symmetrically and separately placed

within the wall thickness. Vertical reinforcement ratios (ρv) were more than the

minimum requirements and varied between 0.0033 and 0.0047. The compressive

cylinder strength of the concrete was between 28 and 42 Mpa and yield strength of

steel ranged from 512.8 to 604.2 MPa. The following conclusions were reached:

i. Under axial and eccentric loading, panels with H/tw values less than 20 failed

by crushing while those with larger values of H/tw failed due to buckling.

The lateral deflections at the instant of failure did not increase dramatically

for H/tw values less than 20, while a dramatic increase was observed for

values more than 20.

ii. The reduction in strength due to an eccentricity of tw/6 of the wall thickness

varied from 18 percent to 50 percent for variation in slenderness ratios from 8

to 28 respectively.

Pillai and Parthasarathy (1977) tested eighteen large scale wall models with

various H/t ratios from 5 to 30. The walls were grouped into three groups; namely

group A, B and C. The walls in group A were provided with the minimum

reinforcement. The group B walls had twice as much steel area as the walls in group

A. The walls in group C were not reinforced. The walls were tested under pinned-

end condition at both ends with applied axial loading until failure. The lateral

deflection at critical points, the axial shortening, and the axial and lateral surface

strain on both faces at critical points were measured at each stage of loading. The

test results showed that steel ratio have small significance on the ultimate strength of

these walls. It was found that the walls with low slenderness ratio, H/t ≤ 20,

generally failed by crushing whereas wall with higher slenderness ratio, H/t > 20,

failed by buckling.

2.3.3 Effect of Shear Connector

Einea et al. (1994) studied experimentally and analytically of connector system in

new developed precast sandwich panel system with high thermal resistance and

19

optimum structural performance. This system using the connector that was made by

fiber reinforced plastic bars with prestressed steel strand chords. The experimental

program included testing of small scale specimens by pure shear and flexural loading

and full scale panels by flexural loading. The analytical investigation included finite

element modeling of the tested small scale specimens and comparisons with theory

of elasticity. It was found that the experimental and analytical results from software

and from theory of elasticity equations correlated well and showed that the

developed panel system meet the objectives of the research.

Further experimental investigation by Mohamad (2010) also studied the

structural behavior of precast lightweight foamed concrete sandwich panel as a load-

bearing wall. Fourteen (14) PLFP panels were involved in this experiment. The

panel consists of two lightweight foamed concrete wythes with 40 mm thickness and

a polystyrene insulation layer in between the wythes. The foamed concrete wythes

in the panels were reinforced with 9 mm high tensile rebar which were tied up to 6

mm steel shear connectors for panels PA-1 to PA-8 and 9 mm steel shear connectors

for panels PA-9 to PA-10 bent to an angle of 45º. The panel’s height is between

1800 mm to 2800 mm and its width is 750 mm. The height of the panel and the

thickness of the polystyrene layer were varied to get various slenderness ratios.

The strength capacity and behaviour of PLFP panel under axial load was

examined by looking at the slenderness ratio and the effectiveness of the shear

connectors. The results were analysed in the context of ultimate strength, load-

deflection, strain distribution and cracking pattern and mode of failure. The strength

capacity and behavior of PLFP panel under axial load was examined by looking at

the slenderness ratio and the effectiveness of the shear connectors. The result

indicates that the wythes of the more slender panels tend to deflect together more in

the same direction compared to the less slender panels. It was also found that crack

appeared at 30% to 70% of the ultimate load and the panels crushed at either one or

both ends of panels due to the material’s failure.

20

2.4 Precast Lightweight Foamed Concrete Sandwich Panel

The sandwich panel is unique in its own way because the materials it uses are

different from any other sandwich panel. Sandwich panel development had started

with normal weight material as both core and faces. However, the use of lightweight

material as core layer has become more familiar in recent years. Review of the

previous studies below will explain the advantage of using the sandwich panel in the

construction field. British Standard, BS 8110: Part 2 (1985) classifies the

lightweight concrete as concrete with density of 2000 kg/m3 or less. Among the

advantages in using the lightweight materials in the precast concrete sandwich panel

are it helps to reduce the self-weight of the panel and overall cost of the construction.

One of the earliest studies on precast concrete sandwich panel was conducted

by Pfeifer and Hanson (1964). The study included 50 reinforced sandwich panels

with a variety of wythe connectors. The panels were tested in flexure under uniform

loading. The test results showed that welded truss-shaped steel connectors are the

most effective connection in transferring the shear force. The study also

demonstrated the beneficial effect of using concrete ribs to connect the wythes.

According to Pessiki et al. (2003), four full scale of PCSP were tested. The

first panel was a typical precast, prestressed concrete sandwich panel that had shear

connector provided by regions of solid concrete in the insulation wythe, metal wythe

connector (M-ties), and bond between the concrete wythes and the insulation wythe.

It was found that the solid concrete region provide most of the strength and stiffness

that contribute to composite behaviour. Steel M-ties connectors and bonded between

the insulation and concrete contribute relatively little to composite behaviour.

Therefore, it is recommended that solid concrete region be proportioned to provide

all of the required composite action in precast sandwich panel wall.

Benayoune et al. (2006) have investigated that the structural behavior of

precast sandwich panels due to eccentric load and the ratio of height to thickness, H/t

ratio. In this study, the Precast Sandwich Lightweight Foam Concrete Panel, PLFP,

with shear truss connectors is typically fabricated of two concrete wythes tied

together with truss-shaped shear connectors equally spaced along the length of the

panel as depicted in Figure 2.6. The structural behaviour of the panel depends

greatly on the strength and stiffness of the connectors, while the thermal resistance of

21

Steel Wire Mesh Insulation Layer Concrete Wythe

the insulation layer governs the insulation value of the panel. Precast sandwich

panel functions as efficiently as precast solid wall panel but differ in their build-up.

Steel Shear Connector

Figure 2.6: Typical Precast Concrete with Truss Shaped Shear Connector (Benayoune et al., 2006)

Pillai and Parthasarathy (1977) conducted an investigation on solid reinforced

concrete about the influence of H/t ratio and steel ratio of the ultimate strength of

sandwich wall panels. It was found that the steel ratio has very little influence on the

ultimate strength of the walls. The result showed that the models with low H/t ratios

generally failed by cracking and splitting near one or both ends of the plates.

However, models with H/t ratio > 20 (higher slenderness wall) fail at the mid depth.

On the other hand, Mohamad and Muhammad, (2011) studied about the

precast lightweight foamed concrete sandwich panel with single and double

symmetrical shear truss connectors under eccentric loading. Figure 2.7 shows the

panel with double diagonal symmetrical steel shear truss connectors. The function of

these shear truss connectors is to sustain the applied load and transfer it from one

wythe to the other. The truss-shaped shear connectors were equally spaced along the

length of the panel as depicted in the figure. The result of this study explains that the

use of symmetrical truss to strengthen the PLFP panel was able to improve its

ultimate strength capacity. The results of the ultimate strength capacity showed that

22

panel PA-2 (with symmetrical truss) had a higher strength at 355 kN than panel PE-1

(single diagonal truss) which was at 188 kN. Therefore, the targeted strength for

panel PE-2 is achieved. For the load-deflection profiles, panel PE-2 showed smaller

deflection measurement than panel PE-1. This indicates that a stronger panel will

deflect lesser. Based on the results, the panels failed at the top and bottom of the

panel but did not crack at the middle part. This is due to premature material failure

which caused local buckling. Despite the failure of the materials which will cause an

early crushing, it is believed that by using the double symmetrical truss, it manages

to help holding the two concrete wythe together.

Figure 2.7: Precast Concrete Sandwich Panel (Source: Mohamad and Muhammad, 2011)

Insulated sandwich panels are widely used to provide a structural shell for

buildings. These panels typically consist of two layers (wythes) surrounding an

insulating layer. The outer layers are usually constructed of precast or prestressed

concrete and are connected through the insulation layer to form a structurally

composite panel. This composite action causes the panel to deflect when the

structural wythe experience differences in temperature or humidity due to the

presence of the insulation wythe (Einea et al., 1994).

Based on the previous research,it can be seen that the research on sandwich

panels are still limited and there are still many weaknesses that arise such as the

research done by Lian (1999). This study discussed about the ultimate limit

23

behaviour of reinforced concrete sandwich panels under axial and eccentric loads.

However, the numbers of the tested panels were so small which were only four (4)

specimens. No generalised inferences could be drawn out of testing on these four

specimens. Therefore, in this research eight (8) specimens will be cast and tested.

The capacity of panel and its behavior could be accurately studied and concluded.

The ultimate load capacity for pure axial loaded panels was proposed based on

expressions for design of solid reinforced walls from the codes and for design of

sandwiched panels from previous research.

From the previous research, it is noticed that most of the panels developed

were made of conventional concrete. Any structural element made from

conventional concrete are normally strong but has lower strength over weight ratio.

Therefore, further research on this type of panel with lightweight materials is very

much in need. The research investigates the structural behavior of Precast

Lightweight Foamed Concrete Sandwich Panel, PLFP, with double shear truss

connectors under axial Load and two Connected PLFP panels under four point

bending load. The aim of this research is to achieve the intended strength for use in

low to medium rise building. Considering its lightweight and precast construction

method, it is feasible to be developed further as a competitive IBS building system.

The result from this research could be used as a guideline for future research to

develop PLFP panel as a walling unit in the industry and the future development of

PLFP as a structural material.

2.5 Advantage of Sandwich Panels

Sandwich construction form has distinct advantages over conventional structural

sections because it promises high stiffness and high strength-to-weight ratio (Tat and

Qian, 2000; Araffa and Balaguru, 2006) as compared with a solid member.

Sandwich composite structure possesses excellent flexural and shear properties.

Their inherent lightweight characteristics make them ideal structural components

where weight reduction is desirable (Serrano et al., 2007). Thus structural sandwich

panels are becoming important elements in modern lightweight construction.

24

In concrete construction, self-weight of structure represents a very large

proportion of the total load on the structures (Mouli and Khelafi, 2006). Thus

reduction in the self-weight of the structures by adopting an appropriate approach

results in the reduction of element cross-section, size of foundation and supporting

elements thereby reduced overall cost of the project. The lightweight structural

elements can be applied for construction of the buildings on soils with lower load-

bearing capacity (Carmichael, 1986).

Reduced self-weight of the structures using lightweight concrete reduces the

risk of earthquake damages to the structures because the earth quake forces that will

influence the civil engineering structures and buildings are proportional to the mass

of the structures and building. Thus reducing the mass of the structure or building is

of utmost importance to reduce their risk due to earthquake acceleration (Ergul et al.,

2003). Among all the advantages, its good thermal insulation due to the cellular

thick core makes it an ideal external construction component (Bottcher and Lange,

2006). Some recent investigations suggest their excellent energy-absorbing

characteristics under high-velocity impact loading conditions (Villanueva and

Cantwell, 2004). Sandwich structures have also been considered as potential

candidate to mitigate impulsive (short duration) loads (Nemat-Nasser et al., 2007).

2.6 Foamed Concrete Fabrication

Foamed concrete is a mixture of cement, fine sand, water and special foam which

once hardened results in a strong, foamed concrete containing millions of evenly

distributed, consistently sized air bubbles and cells. It uses a stable foaming agent

and a foaming generator to create a lightweight concrete. In lightweight foam

concrete, the density is determined by the amount of foam added to the basic cement.

The strength of the concrete is determined by controlled the amount of foam added

into cement mixer.

Foamed concrete is classified as having an air content of more than 25%.

The air can be introduced into mortar or concrete mixture using two methods

(Newman and Choo, 2003). First, preformed foam from a foam generator can be

mixed with other constituents in a normal mixer or ready mixed concrete truck.

133

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iii THE STRUCTURAL PERFORMANCE OF PRECAST WITH … · 2016. 8. 3. · Structural Wall Elements 2.11.1 Plain Concrete Wall 31 2.11.2 Reinforced Concrete Wall 32 2.11.3 Response of