Performance of circular concrete-filled fiber-reinforced polymer-steel composite tube columns under axial compression

A concrete-filled fiber-reinforced polymer-steel composite tube column consisting of inner concrete and an exterior fiber-reinforced polymer-steel tube was studied in this paper. A total of 22 specimens were tested under axial compression to investigate the performance of the circular concrete-filled fiber-reinforced polymer-steel composite tube columns. The main experimental parameters were the thickness of the steel tube, the number of fiber-reinforced polymer layers, the type of fiber-reinforced polymer, and the hybridization of fiber-reinforced polymer, in which basalt-fiber-reinforced polymer was used to manufacture concrete-filled fiber-reinforced polymer-steel composite tube columns and was compared with carbon fiber-reinforced polymer. The test results showed that local buckling of the steel tube can be suppressed and even prevented effectively with fiber-reinforced polymer strengthening, and the compressive strength of the concrete-filled fiber-reinforced polymer-steel composite tube specimens is enhanced by the external fiber-reinforced polymer confinement compared with that of the concrete-filled steel tube specimens. With the increase in the number of fiber-reinforced polymer layers or with a larger ultimate tensile strain in the fiber-reinforced polymer, the peak axial strain corresponding to fiber-reinforced polymer fracture increases accordingly. A new model that considers composite action was developed for strength prediction of concrete-filled fiber-reinforced polymer-steel composite tube columns, and the analytical results agree well with the experimental results.