Torsional behavior of concrete-filled circular steel tube columns

Concrete-filled tubes (CFTs) are columns commonly used in high-rise building construction due to their structural effectiveness. Past studies on CFT have focused primarily on uniaxial compression, bending, and eccentric compression and a few investigations have studied member behavior under combined compression and torsion. In this paper, the behavior of a circular CFT column under combined torsion and compression was theoretically investigated considering the confinement effect of the steel tube, softening of concrete, and spiral effects. Biaxial stress effects due to diagonal cracking were also considered. By incorporating these factors into the compatibility and equilibrium conditions, a basic equation to describe the torsional behavior of the entire loading history of CFT members was derived.