Cyclic behavior and ultimate bearing capacity of circular concrete-filled double skin steel tube members subjected to combined compression and torsion

This paper presents a pseudo-static test investigation and finite element analysis on the behavior of circular concrete-filled double skin steel tube (CFDST) members under axial compression and torsion. The hollow ratio (χ) and axial compression ratio (n) are considered in the test study. The ductility, hysteretic behavior, failure modes, and compression–torsion correlation of circular CFDST members are discussed. The comparison results show that the validated finite element model is capable to capture the behavior of circular CFDST members under compression and torsion. The effect of loading paths and various parameters on the compression–torsion correlation of circular CFDST members are analyzed. Parametric analyses are carried out to investigate the effect of key parameters, such as material properties, nominal steel ratio, the wall thickness of inner steel tube, and hollow ratio on the compression–torsion correlation of circular CFDST members. It can be seen that the circular CFDST members under compression and torsion possess good load-bearing capacity, energy dissipation, and ductility properties. The loading paths, yield strength of inner and outer steel tubes, nominal steel ratio, and the wall thickness of inner steel tubes have little effect on the compression–torsion correlation of the composite members. When the axial compression ratio is less than 0.2, the axial compression load can slightly improve the torque capacity of circular CFDST members. Finally, the compression–torsion correlation equation of these members was proposed by regression analysis, and design formulas with good accuracy for predicting the torque capacity of circular CFDST members under compression and torsion were proposed.