Shear strengthening of sub-standard reinforced concrete beams with CFRP: Influence of fiber areal weight, wrap scheme and concrete strength

This study investigates the effectiveness of carbon fiber-reinforced polymer (CFRP) in enhancing the performance of reinforced concrete beams with insufficient shear reinforcement-a common issue in existing low- and highstrength reinforced concrete buildings. A total of 35 one-third scale beams were tested under four-point bending, considering varying concrete strengths (5-70 MPa), CFRP areal weights (300 and 900 g/m2), and wrapping configurations (full (F), U-shaped (U), and side (S)). Key parameters such as load-displacement behavior, energy dissipation, ductility, and stiffness were analyzed in detail. The results demonstrated that CFRP strengthening increased shear capacity by up to 154 % in low-strength concrete (5-20 MPa), while the improvement was limited to 47.2 % in high-strength concrete. Failure modes were significantly influenced by wrapping type: full wrapping led to a 90 % shift from shear to flexural failure, whereas U-shaped and side wrapping achieved only 40 % and 10 % conversion, respectively. Full wrapping also yielded the highest gains in energy dissipation and ductility, while side wrapping alone was largely ineffective. Interestingly, increasing CFRP areal weight did not result in proportional performance gains; in many cases, the 300 g/m2 application outperformed the 900 g/m2 variant. This suggests that poor interfacial bonding and inadequate epoxy impregnation may hinder the effectiveness of higher areal weight configurations. In conclusion, concrete strength, wrapping type, and CFRP areal weight must be considered collectively in shear strengthening strategies. Among these, full wrapping offers the most consistent and reliable improvements in shear capacity, ductility. and energy dissipation.