Relationships between interfacial behavior and flexural performance of hybrid steel-FRP composite bars reinforced seawater sea-sand concrete beams

Abstract The shortage of freshwater and river sand, as well as steel corrosion are challenges for the construction and maintenance of offshore and marine structures. The combination of seawater sea-sand concrete (SWSSC) with steel-fiber reinforced polymer composite bar (SFCB) provides an alternative solution to address the above issues. However, the understanding of non-uniform strain distribution and inferior bond behavior at steel-FRP-concrete interface is limited, which is critical for the stress transfer and interfacial behavior of tri-layer system, further inducing serviceability concern and causing potential safety risks for SFCBs reinforced SWSSC members. Here, the interfacial behavior of steel-FRP-concrete system was investigated by tensile test and pull-out test, and the corresponding flexural behavior of SWSSC beams with various SFCB reinforcement ratios was studied with fiber Bragg grating (FBG) sensor to quantitatively measure the non-uniform strain distribution. The results show that the inferior bond behavior and non-uniform strain distribution at steel-FRP-concrete interface result in the excessive deflection of beams and unreliable design. Furthermore, a modified model that can accurately predict the real deflection is proposed. The findings can contribute to a safer design tactic and promote the application of SFCBs reinforced SWSSC structures.