Axial compression tests on hybrid double-skin tubular columns filled with high strength concrete

Hybrid FRP-concrete-steel double-skin tubular columns (DSTCs) are of a new form of hybrid structural members recently developed at The Hong Kong Polytechnic University. A hybrid DTSC consists of an inner steel tube, an outer FRP tube and a concrete infill between them. Hybrid DSTCs possess many important advantages over conventional counterparts, including excellent corrosion resistance as well as excellent ductility and seismic resistance. A large amount of research has been conducted on hybrid DSTCs, but the existing experimental studies have been limited to hybrid DSTCs filled with normal strength concrete (NSC). Since hybrid DSTCs are highly ductile and the absence of reinforcing steel bars ensures good-quality casting of high strength concrete (HSC), they offer a promising opportunity for the use of HSC which is more brittle than NSC. This paper presents results from the first series of axial compression tests on hybrid DSTCs with HSC. The parameters examined in the present study include the section configuration, the void ratio, and the properties of FRP tubes and steel tubes. The test results confirm that hybrid DSTCs with HSC possess very good ductility when the outer FRP tube has a sufficiently large strain capacity in the circumferential direction.