Abstract

Concrete filled steel tubular (CFST) column is a kind of composite structure, in which a concrete core is confined within a steel tube. Thanks to the interaction between the steel tube and the concrete core, the compressive load carrying capacity of concrete is increased. This phenomenon is usually referred to as the ``confinement effect''. Correctly modeling the confinement effect, i.e. how the confined concrete behaves under certain types of loadings, is essential in analysis and design of CFST columns. Most of the current works focus on straight columns. In this paper, a novel finite element model is developed in ABAQUS software to analyze the nonlinear behaviors of CFST columns under axial compression, which is suitable for both uniform columns (i.e. the crosssectional area is constant) and tapered columns (i.e. the cross-sectional is continuously varied with respect to the length of the column). The tapered columns are approximated as columns with piecewise constant cross sections, linearly varying from one end to the other end. Geometrically, as the number of piecewise constant cross sections increases, the model converges to the tapered column. In each segment of constant cross-sections, the material behavior of straight column is assumed. Thus, the current model is an extension to existing models for straight CFST columns. Two types of cross sections are investigated: circular shape and rectangular shape. These two cross sections are also the most popular ones in real life. Pre-processing in ABAQUS, i.e. setup of the model, is conducted via a subroutine written in Python script. The ability of the proposed numerical model in load carrying prediction is demonstrated through comparison with experimental data previously reported in the literatures by other authors.