EXPERIMENTAL STUDY ON THE CYCLIC BEHAVIOR OF CONCRETE-FILLED STEEL TUBULAR (CFST) MEMBERS WITH CIRCULAR-SEGMENT GAPS UNDER COMBINED COMPERSSION-BENDING-TORSION LOADING

In order to study the effect of circular-segment gap on the seismic behavior of concrete-filled steel tubular (CFST) members subjected to combined compression-bending-torsion loadings were studied. A total of 16 specimens were tested under constant axial compressive loads and cyclically combined bending and torsion. The tests included eight CFST specimens with circular-segment gaps, six CFST specimens without gaps and two specimens of hollow steel sections. The examined testing parameters included the gap ratio, the axial load level and the bending-torsion ratio. Based on the test results, the effects of circular-segment gap on the failure mode, load versus displacement hysteretic curves, envelope curves, stiffness degradation, energy dissipation and strain development of the CFST specimens were studied. It was found that, the existence of the circular-segment gap had little influence on the shape of the hysteretic curve, whereas it tended to cause a decreased stiffness at the hardening stage of the curve after the ultimate strength was achieved. The ultimate strength, stiffness and energy dissipation ability of the CFST specimens tended to decrease with the increase in the gap ratio. The effect of changing axial load level on the behaviour of CFSTs with gaps was not significant, where the effect of gapson the ultimate strength, stiffness and energy dissipation tended to be more severe with the increase in the bending-torsion ratio. It indicates that the influence of gapson the flexural behavior was more significant than the torsional behaviour of the CFST member.