5. i
Contents
Acknowledgments vi
1 Introduction 1
1.1 Types of composite columns 1
1.2 Advantages of CFST column construction 3
1.2.1 Structural advantages 3
1.2.2 Construction advantages 5
1.3 Characteristics of CFST columns 5
1.3.1 Local buckling of rectangular CFST columns 5
1.3.2 Confinement effects in circular CFST columns 7
1.4 Conclusions 8
1.5 References 8
2 CFST short columns 10
2.1 Introduction 10
2.2 The fiber element method 13
2.2.1 Assumptions 13
2.2.2 Basic concepts 13
2.2.3 Fiber strain calculations 15
2.2.4 Stress resultants 16
2.3 Material constitutive models 17
2.3.1 Structural steels 17
2.3.2 Compressive concrete in rectangular CFST columns 18
2.3.3 Compressive concrete in circular CFST columns 21
2.3.4 Concrete in tension 23
2.4 Local and post-local buckling 24
2.4.1 Initial local buckling 24
2.4.2 Post-local buckling 25
2.4.3 Stress redistribution 27
2.5 Computational procedures 28
2.5.1 Axial load-strain analysis 28

6. ii
2.5.2 Moment-curvature analysis 29
2.5.3 Axial load-moment interaction strength analysis 32
2.6 Numerical solution schemes based on the secant method 32
2.6.1 The secant method 32
2.6.2 Application to beam-column analysis 34
2.7 Section performance indices 35
2.7.1 Steel section performance index 35
2.7.2 Strain ductility index 36
2.7.3 Curvature ductility index 36
2.8 Verification of fiber element models 37
2.8.1 Axial load-strain curves 37
2.8.2 Moment-curvature curves 39
2.9 Behavior of CFST short columns 40
2.9.1 Effects of local buckling 41
2.9.2 Effects of depth-to-thickness ratio 42
2.9.3 Effects of concrete compressive strength 44
2.9.4 Effects of steel yield strength 46
2.9.5 Effects of axial load level 48
2.9.6 Effects of sectional shape 49
2.10 Conclusions 50
2.11 References 51
3 Uniaxially loaded CFST slender beam-columns 57
3.1 Introduction 57
3.2 Analysis of cross-sections 59
3.3 Load-deflection analysis 60
3.3.1 Pin-ended beam-column model 60
3.3.2 Theoretical formulation 61
3.3.3 Computational procedure 62
3.4 Axial load-moment interaction strength analysis 64
3.4.1 Theoretical formulation 64
3.4.2 Computational procedure 66
3.5 Numerical solution methods for uniaxial bending 68
3.5.1 Algorithms based on the secant method 68
3.5.2 Algorithms based on Müller’s method 69
3.6 Comparisons with experimental results 71

7. iii
3.7 Behavior of uniaxially loaded CFST slender beam-columns 73
3.7.1 Effects of local buckling 74
3.7.2 Effects of steel ratio 75
3.7.3 Effects of column slenderness ratio 77
3.7.4 Effects of loading eccentricity ratio 79
3.7.5 Effects of concrete compressive strength 80
3.7.6 Effects of steel yield strength 82
3.7.7 Effects of sectional shape 84
3.7.8 Effects of concrete confinement 86
3.8 Conclusions 88
3.9 References 90
4 Biaxially loaded CFST slender beam-columns 93
4.1 Introduction 93
4.2 Analysis of cross-sections under biaxial bending 96
4.3 Modeling load-deflection responses 96
4.3.1 Theoretical model 96
4.3.2 Equilibrium equations 97
4.3.3 Computational procedure 98
4.4 Modeling axial load-moment strength envelopes 101
4.4.1 Basic concepts 101
4.4.2 Equilibrium equations 102
4.4.3 Computational procedure 103
4.5 Numerical solution methods for biaxial bending 105
4.6 Column performance indices 106
4.6.1 Steel contribution ratio 106
4.6.2 Concrete contribution ratio 107
4.6.3 Strength reduction factor 107
4.7 Verification of numerical models 108
4.8 Behavior of biaxially loaded CFST slender beam-columns 109
4.8.1 Effects on ultimate axial strengths 110
4.8.2 Effects on steel contribution ratio 112
4.8.3 Effects on concrete contribution ratio 115
4.8.4 Effects on strength reduction factor 117
4.8.5 Effects on strength envelopes 120
4.8.6 Effects of loading angle 121
4.9 Conclusions 122
4.10 References 124

8. iv
5 CFST beam-columns with preload effects 126
5.1 Introduction 126
5.2 Initial deflections caused by preloads 128
5.2.1 The fiber element method 128
5.2.2 The load control method 130
5.2.3 Analysis procedure 131
5.3 Load-deflection analysis of CFST columns 133
5.3.1 Theoretical formulations 133
5.3.2 Analysis procedure 134
5.4 Development of strength envelopes 136
5.5 Numerical solution methods 137
5.6 Comparisons with experimental results 137
5.6.1 Circular CFST columns 137
5.6.2 Square CFST columns 138
5.7 Behavior of CFST columns with preload effects 140
5.7.1 Effects of local buckling 140
5.7.2 Effects of preloads on load-deflection curves 142
5.7.3 Effects of preloads on column strength curves 143
5.7.4 Effects of preload and depth-to-thickness ratio 145
5.7.5 Effects of preload and loading eccentricity ratio 146
5.7.6 Effects of preload and steel yield strength 148
5.7.7 Effects of preload and concrete compressive strength 148
5.8 Design for rectangular CFST columns under axial compression 151
5.8.1 Liew and Xiong’s design model 151
5.8.2 Patel, Liang and Hadi’s design model 152
5.8.3 Comparisons of design models 153
5.9 Conclusions 154
5.10 References 155
6 CFST slender beam-columns under cyclic loading 157
6.1 Introduction 157
6.2 Modeling of cross-sectional behavior 160
6.2.1 Assumptions 160
6.2.2 Cyclic constitutive models for concrete 161
6.2.3 Cyclic constitutive models for structural steels 165
6.2.4 Cyclic local and post-local buckling 167
6.3 Modeling of cyclic load-deflection responses 167
6.3.1 Theoretical model 167
6.3.2 Analysis procedure 169

9. v
6.4 Comparisons with experimental results 171
6.5 Cyclic behavior of CFST slender beam-columns 173
6.5.1 Effects of cyclic local buckling 173
6.5.2 Effects of depth-to-thickness ratio 174
6.5.3 Effects of column slenderness ratio 175
6.5.4 Effects of concrete compressive strength 176
6.5.5 Effects of steel yield strength 177
6.6 Conclusions 178
6.7 References 179

10. vi
Acknowledgments
The authors thank all their co-researchers for their contributions to some of the
research works presented in this book, particularly Professor Brian Uy and Scientia
Professor Mark A. Bradford at the University of New South Wales, and Professor Jat-
Yuen Richard Liew at the National University of Singapore. Thanks also go to
Professor Yi-Min Xie at RMIT University, Emeritus Professor Grant P. Steven at the
University of Sydney and Strand7 Pty Ltd, Professor Yeong-Bin Yang at Chongqing
University, Professor Yanglin Gong at Lakehead University, Dr. Sawekchai
Tangaramvong at the University of New South Wales and Professor N. E.
Shanmugam at Anna University for their useful communications and support.
Finally, the authors thank their families for their great encouragement and support.