RESEARCH ON RESTORING FORCE MODEL OF H-SECTION STEEL MEMBERS UNDER UNIAXIAL COMPRESSION AND BENDING CONSIDERING LOCAL BUCKLING

It is the basis of elastic-plastic time-history analysis in seismic analysis of the thin-walled frame structures that the effect of local buckling must be considered in the restoring force model. In order to obtain the moment-curvature relationship of a H-section member under cyclic bending about different axes, the hysteretic properties of uniaxial compression and bending of a thin-walled H-shaped section member were analyzed by FEM. Based on the results of tests and of parameter analysis, a restoring force model was established considering the degradation caused by local buckling and by plate interaction effect. The model is divided into two degradation models according to whether there is increased reloading stiffness in the degradation stage. The first type, the general degradation model, was used for the bending around the weak axis with buckled-web and the bending around a strong axis. The second type, increased reloading stiffness model, was used for the bending around the weak axis with unbuckled-web. The correctness of the proposed restoring force model is verified by comparing the results of tests and of numerical analyses with those of multiple cross sections with different width-thickness ratios and axial compression ratio. The comparison ensures the accuracy and applicability of the model. The model and conclusion presented show that the thin-walled H-section member has a certain ductility and energy dissipation capacity after buckling. This shows that it can be used in seismic design, and provides a design basis for the performance-based design of light steel system buildings.