RESEARCH ON RESTORING FORCE MODEL OF CONCRETE-FILLED STEEL TUBE COLUMNS UNDER AXIAL CYCLIC LOADING

To establish the axial restoring force model of inclined columns, 8 concrete-filled steel tube (CFST) columns were manufactured to conduct the axial cyclic loading test, and to investigate the mechanical mechanism and the restoring force characteristics. Based on the axial cyclic loading test results of CFST columns, the restoring force model of CFST column was fitted through a degenerated three-line model. The dimensionless skeleton curve model of CFST column was established, and the calculation method of the bearing capacity and the corresponding displacement of CFST columns were proposed. Due to the different performance of CFST specimens under axial tension and under axial compression, different hysteresis criteria and unloading stiffness functions were used in positive and negative directions to fit the corresponding unloading stiffness function. Based on these, the axial restoring force model of CFST columns was proposed. The validity of the restoring force model was verified through a comparison with the experimental hysteretic curve, which indicates that the restoring force model established in this paper can accurately predict the hysteretic behavior of CFST columns under axial cyclic load.