Abstract
This paper presents a cyclic loading test study on 2 full-scale stirrup cage confined circular concrete-filled steel tube (CFT) columns and 3 full-scale stirrup cage confined square CFT columns under high axial pressure and low-cycle fatigue horizontal loading. The effect of the contact mode between the stirrup cage and the steel tube wall on the hysteretic behaviours of the specimens was investigated. The failure mode, hysteretic energy dissipation capacity, skeleton curve, elastic stiffness, maximum bearing capacity, ductility index, stiffness degradation, and residual deformation of the confined composite columns were analysed. The results indicate that using stirrup cage in the CFT columns can considerably enhance the seismic performance of CFT columns under high axial force ratio. Welding the stirrup cage to the inner wall of the steel tube can further strengthen the confinement effect of the stirrup cage and steel tube on the infilled concrete while also reducing the amplitude of the drum bending degree and the length of the local buckling region of the steel tube. Therefore, the overall stiffness, maximum bearing capacity and hysteretic energy dissipation capacity of the specimens are improved. Stirrup cage confined square CFT columns with the same design parameters have a greater bending stiffness, maximum bearing capacity and hysteretic energy dissipation capacity compared with those of stirrup cage confined circular CFT columns. The final failure mode of the stirrup cage confined square CFT columns is more favoured than that of the stirrup cage confined circular CFT columns for seismic design; namely, no ductile metal fracture of the steel tube wall on the tensile side was observed.
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