Compression performance of FRP bar-reinforced seawater sea-sand concrete encased FRP-wrapped steel tube columns

This paper developed a new type of composite column made of fibre-reinforced polymer (FRP) bar-reinforced seawater sea-sand concrete (SWSSC)-encased FRP-wrapped steel tubes, which is suitable for maritime engineering. In this composite form, the inner steel tube was isolated to the chloride ions by wrapping with an FRP sheet, and FRP bars were employed to reinforce the exterior SWSSC. To avoid/delay the occurrence of internal steel tube buckling, two measures were implemented, that is, filling with ordinary concrete, and bundling and welding using four hollow small-sized steel tubes. The compression performance was explored by axial compression and eccentric compression tests, and three experimental variables were set, including the steel tube thickness (2.5 mm and 5 mm), number of steel tubes (0, 1 and 4), and eccentricity (20 mm, 40 mm and 60 mm). The test results showed that increasing the thickness of the steel tube could improve the bearing capacity and lateral deformation of specimens (e.g., from 32.66 MPa to 36.99 MPa), whereas the number of steel tubes had a minor positive effect on the specimens. Meanwhile, the bearing capacity of the specimens decreased with increasing eccentricity of the eccentric compression test from 41.51 MPa to 36.99 MPa. Finally, a calculation method was proposed to predict the peak eccentric strength of specimens, which can provide a reference for the design of this kind of composite column.