EQUIVALENT UNIAXIAL CONSTITUTIVE RELATIONSHIP FOR THE ENCASED CONCRETE OF CROSS -SHAPED STEEL TUBULAR WITH BINDING BARS

The behaviors of cross-shaped concrete-filled steel tubular (CFT) stub columns subjected to axial loads were experimentally investigated, including 11 specimens with binding bars and 5 specimens without binding bars. The effects of space and diameter of binding bars, thickness and strength of steel plates and section sizes on the failure mode and bearing capacity are discussed. The results indicate that, with the setting of binding bars, the buckling modes of the steel plates are changed, the local buckling of the steel plates is delayed, and the bearing capacity and ductility of the cross-shaped CFT stub columns are improved. Based on reasonable assumptions, the cross-section is divided into a square section and four rectangular sections, in which the rectangular sections have binding bars while the square section has not. The constitutive relationship of confined concrete is adopted to build the equivalent uniaxial constitutive relationship for the core concrete of each section. The results of load-strain curves calculated by the proposed constitutive relationship are in good agreement with the experimental ones.