Double-tube concrete columns with an FRP outer tube and a high-strength steel inner tube

Hybrid FRP-concrete-steel double-tube concrete columns (DTCCs) are a new type of hybrid columns proposed at The Hong Kong Polytechnic University. A hybrid DTCC consists of an outer tube made of FRP and an inner tube made of steel, with all the space inside the two tubes filled with concrete. This combination of materials is expected to lead to a very ductile, high-strength and corrosion-resistant column, even when both the steel and the concrete have very high strengths. In this paper, the results from a series of axial compression tests on hybrid DTCCs with a high-strength steel (HSS) inner tube are presented to demonstrate the excellent structural response of the new column form with a HSS steel tube. The test results confirm that in a DTCC with a HSS steel tube, the local buckling of the HSS tube is effectively prevented and the concrete is very well confined, leading to a very ductile column response. DTCCs thus provide an effective column form for the efficient use of HSS.