Abstract： In order to study the effects of circumferential gap on the seismic behaviour of concrete-filled steel tubular (CFST) members subjected to combined compression-bending-torsion load, a total of 12 specimens including 8 CFST specimens with circumferential gap, 2 CFST specimens without gap and 2 hollow steel sections, were tested under constant axial compressive load and cyclically combined actions of bending and torsion. The testing parameters included gap ratio, bending-torsion ratio and axial load level. Based on the test results, the failure mode of the CFST with circumferential gap was investigated, and the influences of gap on the hysteretic curve, skeleton curve, stiffness and energy dissipation capacity were experimentally analyzed. It was evident that the existence of circumferential gap could change the failure mode of a CFST specimen, and decrease its ultimate strength, stiffness and dissipated energy. Meanwhile, a finite element model was also established, and the effects of circumferential gap on the strength index and the contact time between outer steel tube and core concrete were investigated by the numerical model. According to the experimental and numerical studies, some suggestions were proposed for the practical CFST structures.
