Hysteresis behaviors and seismic damage model of recycled concrete filled square steel tube columns with the I-shaped steel

To investigate the hysteresis behavior and seismic damage performance of recycled concrete-filled square steel tube columns with I-shaped steel, nine column specimens were subjected to cyclic loading, aiming to acquire their load–displacement hysteretic curves and the effects of recycled coarse aggregate (RCA) replacement rates, I-shaped steel ratio, width–thickness ratio of steel tube, and axial compression ratio on the seismic damage performance of columns. The findings show that the hysteresis curves of these columns are full and exhibit significant ductility, which comprehensively reflects the excellent energy dissipation capacity and seismic behaviors of columns. In addition, the parameter extension analysis was also conducted on the hysteresis performance of columns using OpenSees software. Based on the relevant data from experiments and simulations, combined with the existing earthquake damage model, a modified damage model considering both the deformation and energy dissipation was established in this study, and the seismic behavior levels of columns were divided according to the calculation results of the seismic damage indexes. Finally, the relationships between the seismic performance grades, damage extents, displacement angles, and damage indices of the columns were constructed. The main findings of this study can provide a reference for the seismic damage assessment of these columns.