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

Abstract

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. This research examines the impact of stirrup corrosion on the shear strength of RC beams that have been strengthened with fiber-reinforced polymer (FRP) sheets. The findings have important implications for infrastructure maintenance, especially in coastal or marine environments where steel reinforcements are prone to corrosion. The study demonstrates that both carbon fiber–reinforced polymer (CFRP) and basalt fiber–reinforced polymer (BFRP) sheets can significantly enhance the structural capacity of corroded beams, with BFRP presenting a cost-effective alternative to the more commonly used CFRP. For engineers and practitioners, this research offers practical solutions for extending the life of deteriorating concrete structures. By using FRP sheets, especially BFRP, maintenance costs can be reduced, while maintaining structural safety. The results also show that while FRP strengthens beams, the effectiveness decreases as corrosion levels rise, emphasizing the importance of timely interventions. Additionally, the proposed formula from this study can aid in the design of more resilient and economical repair strategies, particularly for structures in harsh environments.