Assessment of shear behavior of concrete beams reinforced with new-generation GFRP stirrups of different configurations

The maximum permissible strain limit for transverse reinforcement specified in current design codes is a key parameter governing the safety of structural design. However, these codified limits do not adequately capture the performance of the new-generation of glass fiber-reinforced polymer (GFRP) stirrups, leading to unduly conservative predictions of shear capacity. This paper presents a comprehensive experimental and analytical investigation of the shear behavior of concrete beams reinforced with GFRP longitudinal bars and various configurations of GFRP stirrups. Ten GFRP-reinforced concrete beams, with cross-sectional dimensions of 250 × 600 mm and a length of 3100 mm, were tested under four-point bending until failure. The experimental program focused on evaluating the influence of transverse reinforcement ratio and configuration on the shear response of RC beams. The test results demonstrate that increasing the transverse reinforcement ratio significantly enhances the ultimate shear capacity of GFRP-RC beams. Specimens reinforced with GFRP U-shaped stirrups exhibited localized stress concentrations at the bend regions, leading to premature rupture of the stirrups. In contrast, beams reinforced with continuous GFRP spiral stirrups showed improved confinement of diagonal shear cracks and achieved higher shear resistance. The experimental and analytical findings indicate that adopting a transverse reinforcement strain limit of 5000 με provides more rational and accurate predictions of shear strength for various configurations of new-generation GFRP reinforcement. Furthermore, the results indicate that increasing the strain limit to 6000 με has the potential to further improve prediction accuracy, while remaining consistent with observed structural behavior.