Cyclic loading tests and horizontal bearing capacity of recycled concrete filled circular steel tube and profile steel composite columns

To investigate the seismic performance of recycled aggregate concrete (RAC) filled circular steel tube and profile steel composite columns, the cyclic loading tests were conducted for eleven columns. The influences of design parameters on the seismic performance of composite columns were considered and investigated in detail, including the replacement percentage of recycled coarse aggregate (RCA), diameter to thickness ratio of circular steel tube, axial compression ratio, profile steel ratio and section form of profile steel. The failure characteristics, hysteresis loops, skeleton curves, stiffness degradation, ductility and storey drift ratio of columns were presented and discussed in detail. The results show that the column base forms an obvious plastic hinge under the combined action of horizontal cyclic loads and vertical loads, which belongs to the typical compression-bending failure. The hysteresis loops of composites columns are plump and spindle-shaped, indicating good energy dissipation capacity. With the increase of RCA replacement percentage, the ductility and energy dissipation capacity of columns decrease gradually, while the bearing capacity and stiffness of columns firstly reduce and then increase. The seismic performance of columns is significantly improved by the increasing wall thickness of circular steel tube and profile steel ratio. Increasing the axial compression ratio is unfavorable to the seismic performance of columns. The greater the axial compression ratio, the worse the ductility and energy dissipation capacity of column. Based on the test analysis and relevant specifications, the modified formulas on the horizontal bearing capacity of RAC filled circular steel tube and profile steel composite columns were proposed, and the validity of formula was verified by comparing with the test results.