Experimental study on seismic behavior of recycled aggregate concrete filled steel tube columns

To study the seismic behavior of recycled aggregate concrete filled steel tube(RACFST) columns, ten circular specimens with different replacement ratio of recycled coarse aggregate, slenderness ratio, axial compression ratio and steel ratio were tested under the cyclic reversed loading. The entire loading process and failure mode were observed, and the seismic behavior indexes including hysteretic curve, skeleton curve, ductility, dissipation capacity and stiffness degeneration were obtained. The bearing capacity of compression and flexure under the cyclic reversed loading was calculated by several existing codes. It is shown that the failure process and failure mode of RACFCST columns are similar to those of concrete filled steel tube columns. The main phenomenon was that the bottom of the circular steel tube buckled. All the hysteretic curves are plump, whose shapes change from fusiformis to arch. Within the variation range of existing replacement ratio parameter, the hysteretic curves are influenced little. Based on the request for seismic performance, recycled aggregate concrete (RAC) can be used in engineering capacity-bearing structures. The displacement ductility factors are more than 3.0 and the equivalent viscous damping coefficients at failure point are between 0.305 and 0.460. The DL/T 5085-1999 Code can be used to calculate the compression and flexure strength of RACFST columns under the cyclic reversed loading. The research results can provide reference for further extension and application of RACFSRT structures.