FRP-Confined Circular Concrete-Filled Thin Steel Tubes under Axial Compression

Concrete-filled steel tubes are widely used as columns in many structural systems, and a common failure mode of such tubular columns is inelastic outward local buckling near a column end. The use of fiber reinforced polymer (FRP) jackets/wraps for the suppression of such local buckling has recently been proposed and has been proven by limited test results to possess great potential in both retrofit/strengthening and new construction. Against this background, this paper presents the results of an experimental study into the behavior of FRP-confined circular concrete-filled steel tubes (CCFTs) under axial compression, as part of a larger study undertaken at the Hong Kong Polytechnic University aimed at the development of a good understanding of the structural behavior of and reliable theoretical models for CCFTs. The experimental program included three series of tests in which the main parameters examined were the thickness of the steel tube and the stiffness of the FRP wrap. The test results showed that the FRP wrap can substantially delay and even completely suppress the development of local buckling deformation in the steel tube. As a result, both the load-carrying capacity and ductility of concrete-filled thin steel tubes can be substantially enhanced with FRP confinement. The behavior of the concrete was also found to be significantly enhanced by the additional confinement from the FRP wrap.