Compressive performance of high-strength seawater and sea sand concrete-filled circular FRP-steel composite tube columns

A new high-strength seawater and sea sand concrete (HSSC)-filled circular FRP-steel composite tube (HFSCT) structure, consisting of an internal FRP, carbon steel tube and external FRP, was investigated in this study. Thirty-six specimens were tested to investigate the axial behaviour of HFSCTs. FRPs and steel tubes were used as the test parameters. The results indicate that the specimen failure modes change from shear failure to waist drum failure based on the steel tube thickness (4.5-7.0 mm). An increase in the FRP and steel tube significantly affect the axial compressive behaviour of HFSCTs. The ultimate stress of specimens confined by CFRPs is better than those confined by BFRPs; however, specimens confined by BFRPs show excellent ultimate deformation ability. Additionally, 155 axial compressive data samples of concrete-filled circular FRP-steel composite tube columns were collected to establish the test database. The calculation formulas for the ultimate stress, ultimate strain, peak stress and peak strain were developed by considering the efficiency of different FRP types in lateral confinement, which possess a more accurate applicability for concrete-filled circular FRP-steel composite tube columns. Last, a complete calculation model was recommended to predict the full nominal stress-strain curve and accurately reflect the stress-strain behaviour.