Seismic performance of rectangular ultra-high performance concrete filled steel tube (UHPCFST) columns

In this paper, the rectangular ultra-high performance concrete filled steel tube (UHPCFST) specimen columns are tested under combined axial compression and cyclic lateral loading to investigate the seismic performance. The parameters of the steel tube thickness, axial compression ratio and sectional height-width ratio are considered. The test results indicate that the plastic deformation and the cumulative damage are mainly concentrated at column's foot, the failure of the UHPCFST column demonstrates a compression-flexure failure mode. The UHPCFST specimen columns exhibit favourable deformation capacity and energy dissipation ability, and the ultimate drift ratio is within the range of 5.8%-9.8%. Using thick-walled steel tube can delay the stiffness degradation and strength degradation of UHPCFST columns, the reinforcing effect on the core UHPC provided by steel tube becomes strong after the drift ratio exceeds 4%, the vertical strain distribution of steel tube along the height of cross section basically complies with the plain section assumption. In addition, a FE model is estabilished by OpenSees to conduct parametrical analysis. Furthermore, the tested moment bearing capacities of UHPCFST columns are compared with the N-M interaction curves based on current AISC-LRFD, EC4 and AIJ code provisions to evaluate their applicability for UHPCFST columns.