Compressive behavior of hybrid square FRP-concrete-steel double-skin tubular columns with a rib-stiffened inner steel tube

Hybrid fibre-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) consist of an outer FRP tube and an inner steel tube, with the space in between filled with concrete. In hybrid DSTCs, the outward buckling of the steel inner tube is constrained by the surrounding concrete and the outer FRP tube, but its inward buckling is still possible. Existing research has shown that such inward buckling can become significant in non-circular hybrid DSTCs due to the non-uniform confinement, in hybrid DSTCs with a strong FRP tube due to the large axial deformation of the columns, and/or in hybrid DSTCs with a thin steel tube. In these cases, the stiffening of the inner steel tube is necessary to prevent or delay its inward buckling and to minimize its negative consequences to the column behavior. Against this background, a variation of hybrid DSTCs, in which the inner steel tube is stiffened by a number of longitudinal rib stiffeners (hybrid R-DSTCs), was recently developed at the University of Wollongong, Australia. This thesis presents a combined experimental and theoretical study on the axial compressive behavior of hybrid R-DSTCs.