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
4.3.3.1 Ultimate Load 93
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
4.3.4.1 Ultimate Load 101
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
Figure C2 : Tension Testing Result for 4 mm 148
Diameter Reinforcement
Figure C3 : Tension Testing Result for 6 mm 149
Diameter Reinforcement
Figure C4 : Tension Testing Result for 9 mm 149
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
D2 Data for Deflection of PLFP Panel PA 2 154
D3 Data for Deflection of PLFP Panel PA 3 155
D4 Data for Deflection of PLFP Panel PA 4 156
D5 Data for Deflection of PLFP Panel PA 5 157
D6 Data for Deflection of PLFP Panel PA 6 158
D7 Data for Deflection of PLFP Panel PA 7 159
D8 Data for Deflection of PLFP Panel PA 8 160
E1 Data for Surface Strain Readings of PLFP Panel PA 1 161
E2 Data for Surface Strain Readings of PLFP Panel PA 2 162
E3 Data for Surface Strain Readings of PLFP Panel PA 3 163
E4 Data for Surface Strain Readings of PLFP Panel PA 4 164
E5 Data for Surface Strain Readings of PLFP Panel PA 5 165
E6 Data for Surface Strain Readings of PLFP Panel PA 6 166
E7 Data for Surface Strain Readings of PLFP Panel PA 7 167
E8 Data for Surface Strain Readings of PLFP Panel PA 8 168
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
G2 Comparison of Load Bearing Capacity by using Previous 170
Formulae and Classical Formulae for PA 2
G3 Comparison of Load Bearing Capacity by using Previous 171
Formulae and Classical Formulae for PA 3
G4 Comparison of Load Bearing Capacity by using Previous 171
xxi
Formulae and Classical Formulae for PA 4
G5 Comparison of Load Bearing Capacity by using Previous 172
Formulae and Classical Formulae for PA 5
G6 Comparison of Load Bearing Capacity by using Previous 172
Formulae and Classical Formulae for PA 6
G7 Comparison of Load Bearing Capacity by using Previous 173
Formulae and Classical Formulae for PA 7
G8 Comparison of Load Bearing Capacity by using Previous 173
Formulae and Classical Formulae for PA 8
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
Pantelides et al., (2003), tested nine precast concrete wall assemblies with CFRP
Variations in shear area and surface preparation were investigated. Test
results showed that failure of the CFRP composite connection was nonductile,
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
be highly dependent on the geometry and stiffness of the connection.
Mohammed and Nasim (2009) studied the structural behavior of lightweight
sandwich panel which composed of Fiber Reinforced Polymer (FRP) as the wythe
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.
bidirectional FRP wrapping is shown to provide more ductility and toughness
o the panels with unidirectional FRP wrapping (Plain AAC)
13
(Kabir, 2005)
Pantelides et al., (2003), tested nine precast concrete wall assemblies with CFRP
Variations in shear area and surface preparation were investigated. Test
results showed that failure of the CFRP composite connection was nonductile,
that of the steel connection but at three times the lateral load resisted by
The development length of the CFRP composite was found to
be highly dependent on the geometry and stiffness of the connection.
udied the structural behavior of lightweight
sandwich panel which composed of Fiber Reinforced Polymer (FRP) as the wythe
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
bidirectional FRP wrapping is shown to provide more ductility and toughness
(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)
As discussed above, the choice of materials used in sandwich panels have
significant influence on its mechanical properties.
Structural Behaviour of Sandwich Panel
The complex behaviour of sandwich panel is due to its material non
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. The scarcity of information on the behaviour of this
important type of construction is due to the high cost of full scale testing and the
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
As discussed above, the choice of materials used in sandwich panels have
due to its material non-linearity, the
uncertain role of the shear connectors and the interaction between its various
components has led researchers to rely on experimental investigations backed by
n the behaviour of this
important type of construction is due to the high cost of full scale testing and the
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.
the strength of panels decreased nonlinearly with the increase in the slenderness
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
the behaviour of wall panels with various types and sizes of shear connectors.
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
varying from 8 to 28, aspect ratios (H/L) from 1 to 3.5 and thicknesses equal to 75
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
the strength of panels decreased nonlinearly with the increase in the slenderness
: 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
the behaviour of wall panels with various types and sizes of shear connectors.
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)
varying from 8 to 28, aspect ratios (H/L) from 1 to 3.5 and thicknesses equal to 75
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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