Cyclic loading tests and seismic behaviors of steel-reinforced recycled aggregate concrete filled square steel tube composite columns

To investigate the seismic performance of steel-reinforced recycled aggregate concrete (RAC) filled square steel tube composite columns, the cyclic load tests were conducted for nine columns. The effects of steel ratio of profile steel, width thickness ratio of square steel tube, the replacement rate of recycled coarse aggregate (RCA) and axial compression ratio on the seismic performance of composite columns were investigated in detail. The failure characteristics, hysteretic curves, performance indexes and stress-strain distribution of columns were analyzed in detail. The results show that an obvious plastic hinge is generated at the column base and present a compressionbending failure mode. The hysteretic curves of columns present a full shuttle shape, showing that the columns have good energy dissipation capacity and ductility. The use of RCA has little impact on the seismic performance of composite columns. In particular, the bearing capacity of columns with fully RCA is only 1.57% lower than that of ordinary concrete columns. With the increase of profile steel ratio or the decrease of width thickness ratio of square steel tube, the ductility and energy dissipation capacity of columns obviously improve. Increasing the axial compression ratio is conducive to improving the bearing capacity of columns to some extent, but not conducive to improving the energy dissipation and deformation capacity of columns. Based on the failure mechanism of composite columns, combined with AISC specification, the modified formula on the horizontal bearing capacity of steel-reinforced RAC filled square steel tube composite columns is proposed, which is well verified by the test results.