Behavior of concrete-filled steel rectangular hollow sectional columns subjected to cyclic loading

In the past, concrete2filled steel RHS (rectangular hollow section) columns subjected to the axial load and cyclically increasing flexural loading were Seldom studied. The flexural force-deformation behavior of concrete-filled steel RHS specimens was experimentally investigated and the results are presented in this paper. The parameters in the study included the depth-to-width ratio and the axial compressive force-to-axial compressive ultimate capacity ratio. Thirty concrete-filled thin-walled steel RHS specimens were tested under the constant axial load and cyclically increasing flexural loading. A mechanical model is developed in this paper for the concrete-filled steel RHS columns subjected to the constant axial load and cyclically increasing flexural loading. The predicted cyclic responses for the composite columns are in good agreement with the test results. Based on the theoretical model, the parametric analysis was performed on the behaviors of moment versus curvature response, lateral load versus lateral displacement relationship, as well as the ductility coefficient for the composite specimens. Finally, simplified models for the moment versus curvature response, and the lateral load versus lateral displacement relationship, and for the ductility coefficient are suggested.