Behavior of concrete-filled FRP tube columns internally reinforced with FRP-steel composite bars under axial compression

Abstract

Although concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) columns (CFFTs) have become increasingly popular, CFFTs has a weak bending performance as the orientation of the fibers in the FRP tube is generally close to the transverse direction. To this end, this paper proposes novel Concrete-Filled FRP Tube columns internally reinforced with FRP-steel Composite Bars (referred to as CFFT-CB columns) which consist of an external FRP tube, some longitudinal reinforcing FRP-steel composite bars (FSCBs), an FSCB spiral and concrete filled in the entire section. In this study, FSCBs are composed of separated FRP bars and steel bars due to fabrication difficulty. The axial compressive behavior CFFT-CB columns is studied experimentally in this paper. The effects of the spiral type, the spiral pitch, and the thickness of the FRP tube are carefully investigated and the test results confirm the effectiveness of the proposed columns. The ultimate condition of concrete in test columns are compared with four existing stress–strain models, with the confining stresses from both the FRP tube and the FSCB spiral being accounted for. The durable CFFT-CB columns are particularly suitable for marine and coastal structures constructed in harsh environment.