Concrete-filled steel tube columns (CFT) are widely used in high-rise buildings, bridges, and heavily loaded structures. The confinement of concrete by transverse steel tube is effective in improving the ductility and strength of these composite columns. Current design codes tend to underestimate the ultimate strength of CFT columns. In this paper, an accurate modeling for CFT columns is achieved by using the nonlinear three-dimensional finite element method. Columns of circular, square, and rectangular cross-sections are considered. The confinement-sensitive concrete compression model and a suitable constitutive relationship are used for modeling the concrete core and the steel tube, respectively. The bond-slip between the steel tube and the concrete core is incorporated in the model. The results obtained from the proposed analytical model are compared with the measured ones obtained from the available experimental works that was conducted by other researchers. In addition, comparisons of strengths of CFT columns calculated using five different buildings codes and the present analytical model are given. The comparisons indicated that, the present model is accurate enough to predict the prepeak and postpeak behaviors as well as the strength of CFT columns. Furthermore, the proposed model may serve as a means to improve the design code formula for such columns.
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