Abstract: To study axial compression performance and nonlinear mechanical performance of recycled concrete composite columns with square steel tubes, based on the axial compression performance test of recycled concrete composite columns with square steel tubes, a refined model of composite columns was established by using nonlinear finite element software ABAQUS, and its axial compression performance was analyzed by nonlinear numerical model. On this basis, the effect of recycled aggregate concrete strength grade, tie bar spacing, stirrup spacing, square steel tube wall thickness and slenderness ratio on axial compression performance of composite columns were further expanded and analyzed. The stress strain nephogram and load-displacement curves of composite columns were obtained. The results show that the experimental results are basically consistent with numerical simulation results, which also verifies the rationality of finite element model of composite columns. At the end of loading, the middle part of composite columns is damaged by bulging, which shows that the protective layer of recycled concrete is crushed and falls off, the steel bars and steel tubes are locally bulging, and the core recycled concrete is crushed. With the increase of strength grade of recycled concrete, the bearing capacity and energy dissipation of composite columns gradually increase. Setting tie bars can significantly improve the bearing capacity and energy dissipation of composite columns, but the ductility is only slightly improved. The bearing capacity, ductility and energy dissipation of composite columns decrease with the increase of stirrup spacing and slenderness ratio. With the increase of the wall thickness of square steel tubes, the bearing capacity, deformability and energy dissipation capacity of composite columns are significantly enhanced.

Key words: square steel tube, recycled concrete, composite column, axial compression performance, nonlinear analysis