Effective usage of high strength steel tubes: Axial compressive behavior of hybrid FRP-concrete-steel solid columns

Abstract The novel form of hybrid columns, being fiber-reinforced polymer (FRP)-concrete-steel solid columns (FCSSCs), involves the FRP tube and the steel tube as the confining system for the concrete. The buckling of the inner steel in FCSSCs is effectively delayed by the surrounding concrete while the strength of the steel is sufficiently utilized, with it being protected by the outer FRP tube against environmental attacks. A pilot experimental program is conducted to investigate the behavior of axially loaded FCSSCs with an outer polyethylene terephthalate (PET) FRP tube. The experimental results have demonstrated that the axial load carrying capacity of an FCSSC is much larger than the total resistances of the hollow steel tube and the concrete-filled FRP tube. The test FCSSCs possess a monotonically ascending load-strain response with an excellent ductility. The comparisons between the test results and the predictions from existing models demonstrate that one existing model gives satisfactory estimations on the ultimate axial stress and strain of the confined concrete in FCSSCs, while they are incapable to accurately predict stress-strain curves of the confined concrete in FCSSCs.