Seismic behaviour of concrete-filled corrugated steel tubes under cyclic combined compression-bending-torsion loads

Concrete-filled galvanized corrugated steel tube (CFCST) is a novel composite member suitable for use in areas with anti-corrosive and seismic-resistant requirements. Preliminary works have been conducted on its compressive, flexural, shear, and torsional behaviours. However, the seismic behaviour of the CFCST member under combined compression-bending-torsion loads is unclear and needs to be studied. This study therefore presents an experimental investigation of the CFCST member under cyclic combined compression-bending-torsion loads. The main test variables comprise torsion to bending moment ratios, axial compression ratios, and specimen types. The failure modes, hysteretic curves, skeleton curves, ultimate bearing capacities, ductility, energy dissipation capacities, and stiffness/strength degradations are carefully addressed. The cyclic working mechanisms of the CFCST member under combined loads are discussed, with a particular explanation of the correlation relationships. The cumulative damage effects caused by cyclic loading modes have also been analyzed, and finally, the applicability of the simplified design model for the cyclic combined compression-bending-torsion loads is examined.