Influence of Stirrup Corrosion on the Shear Strength of Reinforced Concrete Beams Strengthened with FRP U-Wraps

The corrosion of steel stirrups in RC beams reduces their shear capacity and bond strength with concrete and facilitates premature debonding of the concrete cover, thus affecting the strengthening effectiveness of fiber-reinforced polymer (FRP) sheets. While carbon fiber-reinforced polymer (CFRP) is commonly used, investigations on more affordable basalt fiber-reinforced polymer (BFRP) sheets for strengthening corroded RC beams remain limited. This study experimentally investigates the influence of stirrup corrosion levels on the strain profile and shear strengthening efficiency of corroded RC beams strengthened with CFRP/BFRP sheets. Nine large-scale RC beams are tested under four-point bending, varying stirrup corrosion levels (0%, 15%, and 30%), and FRP type (CFRP and BFRP). The results show that CFRP and BFRP sheets enhance the shear capacity of corroded beams by up to 35% and 34%, respectively, making BFRP a viable alternative to CFRP. The corrosion level greatly influences FRP strain, with maximum strain increases of 59% for CFRP and 104% for BFRP compared with noncorroded beams. However, strengthening efficiency reduces by 5%-12% with increased stirrup corrosion. FRP sheets increase energy absorption capacity and deformation ductility, although these benefits diminish with higher corrosion. An empirical formula is proposed to predict the shear contribution of FRP sheets considering their interaction with corroded stirrups.