CFDST stub columns subjected to large deformation axial loading

This paper reports a series of tests on CFDST (concrete-filled double skin tube) stub columns subjected to large deformation axial loading. Both the outer and inner tubes are circular hollow sections (CHS) with a diameter-to-thickness ratio ranging from 19 to 96. It was found that CFDST significantly improved the behaviour of CHS in terms of failure modes, load carrying capacity and energy absorption. Multiple folds were formed in CFDST under large deformation axial loading. The load drop during cyclic loading was found to be insignificant (about 20 to 30%). The behaviour after the cyclic loading was influenced by the stage of the cyclic loading and the D / t ratio.