Behaviour ofhybrid double-skin tubular columns subjected to combined axial compression and cyclic lateral loading

Hybrid FRP-concrete-steel double-skin tubular columns (hybrid DSTCs) are a new form of hybrid columns developed at The Hong Kong Polytechnic University. They consist of an outer tube made of fibre reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. In these hybrid DSTCs, the three constituent materials are optimally combined to achieve several advantages not available with existing forms of columns, including their superior corrosion and seismic performance. This paper presents the test results of a series of large-scale hybrid DSTCs subjected to combined axial and cyclic lateral loads, with an emphasis on the effect of a high strength concrete infill. All column specimens had a circular section with a diameter of 300 mm and a height of 1350 mm (from the point of lateral loading to the top surface of the stiff RC footing). The parameters examined include the concrete strength, the confinement stiffness of the GFRP tube and the axial load ratio. The test results showed that these hybrid DSTCs possess excellent ductility and hence excellent seismic resistance even when high strength concrete with a cylinder compressive strength of around 120 MPa is used.