Abstract

This paper presents the behaviour and design of axially loaded concrete-filled steel tube circular stub columns. The study was conducted over a wide range of concrete cube strengths ranging from 30 to 110 MPa. The external diameter of the steel tube-to-plate thickness (D/t) ratio ranged from 15 to 80 covering compact steel tube sections. An accurate finite element model was developed to carry out the analysis. Accurate nonlinear material models for confined concrete and steel tubes were used. The column strengths and load–axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled compact steel tube circular stub columns. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results of the parametric study, it is found that the design strengths given by the American Specifications and Australian Standards are conservative, while those of the European Code are generally unconservative. Reliability analysis was performed to evaluate the current composite column design rules.

Keywords: Composite columns; Concrete; High strength; Steel tubes; Finite element; Modeling; Confinement; Structural design

Nomenclature

Cross-sectional area of concrete

Cross-sectional area of steel tube

Correction factor in reliability analysis

COV

Coefficient of variation

D

External diameter of steel tube

Young’s modulus of confined concrete

Mean value of fabrication factor

f

Equivalent uniaxial stress

Unconfined compressive cylinder strength of concrete

Confined compressive strength of concrete

Unconfined compressive cube strength of concrete

Lateral confining pressure

Ultimate stress of steel tube

Yield stress of steel tube

K

Ratio of flow stress in triaxial tension to that in compression

k₁

Coefficient for confined concrete

k₂

Coefficient for confined concrete

k₃

Coefficient for confined concrete

L

Length of column

Mean value of material factor

Ultimate load obtained from ACI/AS

Ultimate load obtained from EC4

Ultimate load obtained from finite element analysis

Mean value of tested-to-predicted load ratios

Ultimate load obtained from test

R

Coefficient for confined concrete

Coefficient for confined concrete

R_ε

Coefficient for confined concrete

R_σ

Coefficient for confined concrete

r

Reduction factor for confined concrete

t

Plate thickness of steel tube

Coefficient of variation of fabrication factor

Coefficient of variation of material factor

Coefficient of variation of tested-to-predicted load ratios

X

Local x-coordinate

Y

Local y-coordinate

Z

Local z-coordinate

ε

Equivalent uniaxial strain

Unconfined concrete strain

Confined concrete strain

Ultimate strain of steel tube

β

Material angle of friction

β

Reliability index (safety index)

Resistance (capacity) factor

Poisson’s ratio of confined concrete

η₁,η₂

Coefficients of confinement for concrete and steel

Article Outline

Nomenclature

1. Introduction

2. Finite element modeling

2.1. General

2.2. Finite element type and mesh

2.3. Boundary conditions and load application

2.4. Material modeling of steel tubes

2.5. Material modeling of confined concrete

2.6. Concrete–steel tube interface

3. Verification of finite element model

3.1. Experimental results

3.2. Comparison of finite element results with experimental results

4. Parametric study and discussion

5. Comparison with design rules

6. Reliability analysis

7. Conclusions

Acknowledgements

References