Abstract
CFT (Concrete Filled steel Tubular members) has attracted much attention because of its structural superiority, especially after the Hanshin -Awaji Earthquake. However, the increase of weight by filling with concrete inside is one of problem associated with CFT. Thus in this study, to reduce the self-weight of CFT, CFDT (Concrete Filled Double-skin steel Tubular members) and CFFT (Concrete-Filled FRP-steel Tubular members) are proposed particularly for higher bridge piers. It is shown by four points bending tests that CFDT has higher bending strength than CFT. But buckling of the outer steel tubes occurred. If the buckling can be effectively prevented, CFDT would have even higher bending strength and ductility. As for CFFT, it becomes clear that the circumferential constrain of outer sheet exhibits especially after the concrete reaches its fracture with dilation of filled concrete.
