Compressive Behavior of PET FRP-confined Concrete-filled Square Steel Tube with Seawater Sea-Sand Concrete Core

Abstract Seawater sea-sand concrete (SSC) instead of ordinary concrete have attracted increasing attention in marine engineering for sustainable development. Fiber-reinforced polymer (FRP)-confined SSC can enhance its mechanical behavior, but the confinement effectiveness and ductility are insufficient for square columns. Concrete-filled square steel tube with circular FRP-confined concrete core (SCFC) members have shown favourable structural performance, but early buckling of the outer steel tube causes the sandwich concrete to fracture prematurely. In such cases, external FRP confinement may delay steel tube outward buckling and provide constraints to the column as well as good corrosion resistance. Therefore, a novel composite column termed FRP-confined SCFC columns with SSC core was proposed. A total of three groups of large rupture strain polyethylene terephthalate (PET) FRP-confined SCFC columns (FSCFCs) along with three groups of SCFC columns were conducted under uniaxial compression. The influences of test parameters including the content of the outer FRP tube and the thickness of steel tubes were analyzed. The test results indicated that the specimens’ peak and residual loads rose in proportion to the content of the outer FRP tubes and the thickness of the steel tubes. The PET FRP tube can effectively restrain the steel tube and reduce the hoop strains that the residual loads increased up to approximately 27% with three-layer fibers. These proposed FSCFCs help exploit ocean resources and promote high-performance structures in harsh marine environment.