Hysteretic behavior of biaxially loaded high strength concrete-filled square hollow section beam-columns

This paper presents a low cycle test on 4 high strength concrete-filled square hollow section (SHS) beam-columns under axial load and biaxial bending moment. The parameters in the study include axial compression ratio (0.433~0.624), width-to-thickness ratio (30 and 50) and slenderness ratio (18.5 and 25.4). The experimental results showed that the specimens have better hysteretic properties and ductility (μ = 3.63~5.18). The bearing capacity and ductility of the specimens decrease with the increase of axial compression ratio; and the bearing capacity increases as the width-to-thickness ratio increases. Fiber-based model is employed to calculate the load-deformation hysteresis curves of specimens and the corresponding results agree well with the experimental results. The cross-sectional parameters of such member are analyzed, and the effects of confinement index, axial compression ratio, load angle and load type on the behavior of the specimens are investigated in details with fiber-based model. Simplified models for the moment-curvature response and load-restoring force are suggested. Results from the suggested models show good agreement with the experimental results, and the models can be applied to elastoplastic dynamic analysis of structures.