Shear behavior of concrete beams reinforced with new-generation GFRP bars and stirrups: Experimental and theoretical strain limit analysis

The shear design of reinforced concrete (RC) beams is over-specified in the current North American design standards and provisions, mainly due to limited experimental data and an early manufacturing process. This approach restricts the optimal use of glass fiber-reinforced polymer (GFRP) stirrups, thereby limiting their full potential in structural engineering applications. The recent development of a new-generation of high-strength GFRP-bar technology, however, has led to significant improvements in the mechanical properties and reliability of bent GFRP stirrups, allowing the possibility to relax current strain limits without compromising concrete integrity. The study undertook a comprehensive experimental and analytical assessment of the shear response of concrete beams reinforced with new-generation high-modulus glass-FRP longitudinal reinforcement and stirrups. Eleven full-scale GFRP-RC beams with identical cross sections and varying total lengths were constructed and tested to failure. The test parameters included transverse reinforcement ratio, stirrup size, and shear span-to-depth ratio. The experimental results indicate that increasing the transverse reinforcement ratio was more effective in enhancing shear strength than increasing the stirrup size, which was found to have no significant impact on shear strength. In contrast, an increased shear span-to-depth ratio was found to diminish shear strength and influence the failure mode. The theoretical analysis revealed that the strain limits currently prescribed in North American design codes (ACI 440.11–22, CSA S806–12, AASHTO LRFD-18, and CSA S6–19) produce conservative shear-strength predictions compared to the experimental findings. As a result, the study advanced a modified strain-based design limit that incorporates the improved strength characteristics of new-generation GFRP-stirrup technology, leading to more reliable and less conservative shear capacity predictions than those obtained using existing code provisions. ● Eleven full-scale GFRP-RC beams tested with varying shear parameters. ● Shear strength improved more by stirrup ratio than by stirrup size. ● Larger shear span-to-depth ratios reduced shear strength and altered failure mode. ● New-generation GFRP stirrups exceeded current code strain limits. ● Proposed strain limit improves accuracy of shear design provisions.