Revisiting the shear design equations for concrete beams reinforced with FRP rebar and stirrup

Current design guidelines and codes use modified shear equations for calculating the shear strength contribution of fiber reinforced polymer (FRP) transverse reinforcement (stirrup) in concrete beams reinforced with longitudinal steel or FRP rebar. These equations, originally developed for steel as longitudinal and transverse reinforcement, are semi-empirical in nature and were developed with a core analytical equation where the coefficients were determined from regression analysis. Here, a comparative study among various code equations was conducted to predict the shear strength of FRP reinforced concrete beams. To facilitate this comparison a database was established from the published literature, which was composed of slender concrete beams (shear span to depth ratio, a/d >2.5) with FRP longitudinal and transverse reinforcement. The database contained 114 beams without transverse reinforcement and 46 beams with transverse reinforcement. The guidelines, codes and models that were implemented and compared in this study consisted of ACI 440.1R-06, JSCE 1997, CNR-DT 203, CSA S806-02, CSA S6-06, unpublished CSA S6-06 Addendum, ISIS-M03-01, simplified Modified Compression Field Theory, cracked section analysis model and modified Zsutty equations. It was observed from the statistical analysis that the CSA S806-02 produced greater coefficients of variation than the CSA S6-09. The ACI 440.1R-06 and JSCE 1997 produced more conservative results in calculating the transverse shear strength. The CSA S6-09 Addendum exhibited the best all-around performance in predicting the shear contribution of FRP reinforced beams compared to that of other design codes and guidelines.