Fiber-reinforced polymer (FRP)-retrofitted concrete structures are extensively utilized, and they have attracted growing research interest due to their combined performance in marine environments. To investigate the effect of seawater exposure, a total of 20 single-shear GFRP (glass-FRP)-bonded concrete structures were tested. Three corrosion conditions, i.e., exposure to single-salinity and triple-salinity seawater through wet–dry cycles as well as continuous immersion in triple-salinity seawater, were simulated and tested. The minimum shear strength (13,006 N) was tested using specimen B150-T-DW-90, which was cured in triple-salinity seawater with wet–dry cyclic exposure. The results of the shear strengths, load–displacement curves, interfacial shear stresses, and fracture energies indicated that seawater exposure degraded the bonding strength of the GFRP–concrete interface. Notably, the wet–dry cycles in triple-salinity seawater resulted in the most significant interface degradation, which could exacerbate with prolonged exposure. By introducing a parameter, the residual coefficient α, a new strength calculation model for GFRP–concrete exposed to a seawater environment was proposed and discussed.

This paper conducts an experimental study on the axial compressive performance of FRP-steel-concrete composite columns. Nine short columns were produced and evaluated in the study, comprising of three concrete-filled steel tube reference columns and six FRP-steel-concrete composite columns, respectively denoted as “reference columns” and “composite columns”. Two categories of failure modes, including shear failure and waist drum, were observed from the experiments. The failure mode may trend toward waist drum from shear failure as more FRP layers were used. The number of FRP layers had a direct effect on the level of compressive strength attained, with a greater number of layers resulting in a greater increase in compressive strength. Moreover, a greater tensile strength and higher elastic modulus of CFRP sheets are more effective at improving the compressive stiffness of the columns. Finally, a four-stage confinement mechanism for FRP-wrapped steel tube concrete composite columns is proposed and discussed, through which the damage mechanisms of the composite structures are more rationally characterized.