Mechanical performance study on recycled aggregate concrete filled steel tubes under axial compression

In order to research the performance evolution of recycled aggregate concrete filled steel tubular (RACFST) members under axial compression, ten specimens were tested according to the parameters of recycled coarse aggregate (RCA) replacement ratio, slenderness ratio and cross-sectional form. Based on the tests, the axial compression load-displacement curves were obtained and the influences of test parameters on the deformation ductility, energy dissipation and stiffness of specimens were analyzed. The results show that the biggest difference of load-displacement curves between circular and square specimens is that the peak point is very sharp in the curves of square specimens. With the increase of RCA replacement ratio, the energy-dissipating capacity and elastic axial compression stiffness of circular specimens are improved, while for square specimens, the energy-dissipating capacity drops first and then increases, and the elastic axial compression stiffness increases first and then drops. The ductility coefficient of RACFCST is larger than that of CFCST, while the ductility coefficient of CFSST is larger than that of RACFSST. An increase of RCA replacement ratio leads to the decrease of the energy-dissipating capacity and elastic axial compression stiffness but the increase of the ductility coefficient of RACFST members. The energy-dissipating capacity and deformation performance of circular steel tubes are superior to those of square steel tubes.