Axial compression behaviour of seawater sea sand concrete columns reinforced with hybrid FRP-stainless steel bars

Using fiber-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete columns in harsh environments has become an important method for solving corrosion problems. The brittleness of FRP bars significantly reduces the ductility of columns. It has been proposed that columns can be reinforced with hybrid FRP and steel bars to improve ductility, but related research is very limited. In this research, the axial compression behaviour of seawater sea sand concrete (SSC) columns reinforced with hybrid FRP bars and stainless steel (SS) bars was studied. In total, 84 SSC columns were designed, including 15 SS reinforced SSC (SS-SSC) columns, 15 glass-FRP (GFRP) reinforced SSC (GFRP-SSC) columns, 45 hybrid FRP-SS reinforced SSC (FRP-SS-SSC) columns and nine plain SSC columns. The failure modes, load-axial displacement curves, bearing capacity, and ductility were analyzed with consideration of the effects of the reinforcement types, reinforcement ratios, and concrete strength. The results showed that ductility could be significantly improved by hybrid reinforcements, and the ductility indexes of the FRP-SS-SSC columns were close to those of the SS-SSC columns. The proposed equation could accurately predict the bearing capacity of SSC columns Furthermore, the theoretical stress-strain relationship for the studied axial compression SSC columns was proposed.