Nonlinear analysis of square concrete-filled double-skin steel tubular columns under axial compression

Abstract

This paper studies the characteristics of square concrete-filled double-skin steel tubular (CFDST) short columns with inner circular steel tube by performing a series of nonlinear finite element (FE) analysis. The precise definitions of the behavior of the material are the initial requirement of numerical modeling. The existing models for predicting the behavior of the concrete core confined by the circular tube are not suitable since the mechanism of the concrete confinement in square composite columns is different from that of the circular ones. Also, ignoring the confinement effects on improving the concrete strength may lead to conservative results. In this paper, the confinement effects provided by the steel tubes on the concrete core in square CFDST columns are taken into account in the concrete constitutive model. The verified FE model is utilized to investigate the effects of important parameters on the ultimate axial strength, energy absorption capacity, ductility, and interaction performance of CFDST columns. A new design equation is suggested based on stress distribution over the concrete cross-section. It is shown that material properties and dimensions of composite columns can highly affect their performance. Also, the thickness of the inner tube must be controlled to prevent its premature failure. Validation of the design equation shows that it leads to the satisfactory predictions of the ultimate strengths of square CFDST short columns under axial loading.