Concrete-filled thin-walled steel SHS and RHS beam-columns subjected to cyclic loading

The flexural force-deformation behavior of concrete-filled thin-walled steel SHS and RHS beam-columns was experimentally investigated and the results presented in this paper. The parameters in the study included the depth-to-width ratio (β), the core concrete strength (f_cu), and the axial load level (n). Thirty concrete-filled thin-walled steel SHS and RHS beam-column specimens were tested under constant axial load and cyclically increasing flexural loading. A mechanics model is developed in this paper for concrete-filled steel SHS and RHS columns subjected to constant axial load and cyclically increasing flexural loading, and is a development of the analysis used for monotonically loading condition (Han et al., 2001). The predicted cyclic responses for the composite columns are in good agreement with test results. Based on the theoretical model, parametric analysis was performed on the behaviors of moment (M) versus curvature (φ) response, lateral load (P) versus lateral displacement (Δ) relationship, as well as ductility coefficient (μ) for the composite beam-columns. Finally, simplified models for the moment (M) versus curvature (φ) response, and the lateral load (P) versus lateral displacement (Δ) relationship were suggested. Formula should be suitable for incorporation into building code, for the calculation of the ductility coefficient (μ) of the composite beam-columns under constant axial load and cyclically increasing flexural loading was developed.