The effect of compression reinforcement on the shear behavior of concrete beams with hybrid reinforcement

This study examines the impact of compression reinforcement on the shear behavior of concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars, steel bars, and a hybrid combination of both. Understanding this relationship is crucial, as the use of GFRP in concrete beams, while beneficial for its corrosion resistance and sustainability, often results in lower stiffness and reduced shear capacity compared to traditional steel reinforcement. The primary objective is to determine how varying levels of compression reinforcement can enhance the shear performance of GFRP-reinforced beams, thereby addressing a significant gap in the literature regarding the efficiency of such systems. Nine beams (1200 × 150 × 250 mm) were tested under a three-point loading system and categorized into three groups based on the GFRP-to-steel reinforcement ratio in the tensile region: T1 (100% steel), T2 (50% GFRP, 50% steel), and T3 (100% GFRP). Each group included three beams with varying amounts of compression reinforcement (0%, approximately 50%, and approximately 100% of the tensile reinforcement). The results show that beams fully reinforced with GFRP had significantly lower ultimate load capacity compared to those with hybrid or steel reinforcement. Adding compression reinforcement notably improved shear strength, reduced deflections, and limited crack formation, especially in beams with the highest compression reinforcement. Hybrid reinforcement of GFRP and steel bars in the tensile region, paired with adequate compression reinforcement, proved to be an optimal reinforcement strategy. This approach balances stiffness and ductility, and enhances the shear capacity and overall performance of concrete beams compared to those reinforced only with GFRP.