CFRP Strengthening of RC Beams with Openings Under Impact Loads

Abstract The integration of web openings in reinforced concrete (RC) beams significantly reduces their shear capacity and impact resistance. This research uniquely investigates the full-scale flexural and shear behavior of un-designed RC beams with web openings subjected to low-velocity impact loading (14715 J). The study systematically varies opening location (midspan versus shear zone) and aspect ratio (width: 0.75h, 1.0h, 1.5h, and 2.0h, depth: 0.2h, 0.3h, 0.4h; h = beam height) while maintaining a constant opening area. The effectiveness of externally bonded carbon fiber-reinforced polymer (CFRP) reinforcement in mitigating the detrimental effects of these openings is numerically investigated. Novel findings indicate that RC beams with smaller openings in the shear zones do not necessitate further strengthening, whereas larger shear-zone openings benefit considerably from CFRP, reducing peak deflections up to 8.9% using one CFRP layer. For beams with one midspan opening, positioning the opening optimally within the tension zone above the tensile reinforcement is shown to maximize the top chord's effective depth, thereby enhancing CFRP's impact resistance effectiveness, with peak deflection reductions of up to 26.18%. This study demonstrates that top chord CFRP reinforcement effectively prevents localized failure and enhances load transfer in RC beams with midspan openings under dynamic loading, offering improved retrofitting solutions for impact resistance.