Experimental study on seismic performance of steel reinforced recycled concrete filled square steel tube composite columns under cyclic loading

To investigate the seismic performance of steel-reinforced recycled aggregate concrete filled square steel tube composite columns, the seismic failure characteristics of 9 specimens were analyzed by the low-cyclic repeated loading tests. The effects of the replacement rate of recycled coarse aggregate, steel ratio of profile steel, width to thickness ratio of square steel tube and axial compression ratio on the seismic performance indicators of composite columns, including the bearing capacity, ductility, and energy dissipation capacity, were studied in detail. The results indicate that the composite columns exhibit typical plastic hinge failure mode under cyclic loading. The load-displacement hysteresis curves of composite column show a full “spindle” shape, indicating excellent energy dissipation capacity. There was minimal effect on the bearing capacity of composite columns of the replacement rate of recycled coarse aggregate. With the increase of the replacement rate of recycled coarse aggregates, the ductility and energy dissipation capacity of the composite columns gradually decreased, with a maximum decrease of 7.83% and 7.6% respectively. The bearing capacity of the composite columns initially increases and then decreases, with the maximum variation in bearing capacity being 1.98%, reflecting a relatively minor impact. The bearing capacity and ductility of composite columns were improved by reducing the width to thickness ratio of square steel tube or increasing the steel ratio of profile steel. The width to thickness ratio of square steel tube decreases from 100 to 33, which results in an increase of 57.44% in the bearing capacity. As the steel ratio of profile steel increases from 4.2% to 6.3%, the bearing capacity and ductility increase by 21.45% and 20.44%, respectively, indicating that the width to thickness ratio of square steel tube and the steel ratio of profile steel have greater influence on the seismic performance of the composite columns. In addition, increasing the axial compression ratio is unfavourable to the seismic performance of composite columns. The hysteresis curve fullness of the composite columns decreases and the ductility decreases as the axial compression ratio increases. When the axial compression ratio increases from 0.2 to 0.6, the ductility of composite columns decreases by 11.11%. The research findings can offer guidance for the seismic design of composite columns. © 2024, Central South University Press. All rights reserved.