Comparative analysis of design guidelines for FRP contribution to shear capacity of strengthened RC beams

Abstract

In the past few years, strengthening and retrofitting of reinforced concrete (RC) structures using externally bonded (EB) fiber-reinforced polymers (FRP) laminates has been deemed as a promising rehabilitation technique. Structural applications of FRP include flexural and shear strengthening of RC beams and confinement of columns. Many guidelines and standards were developed to predict the contribution of FRP to the strength of structural members. For shear strengthening applications, in particular, most of the design guidelines tend to underestimate the capacity of the strengthened members, whereas other models provide unsafe predictions. The accuracy of the models is dependent on many factors, such as but not limited to the wrapping scheme, amount of internal shear reinforcement, shear crack angle, concrete compressive strength, number of FRP layers, and FRP type. For this purpose, this paper focuses on comparing and evaluating the accuracy of the available FRP shear design guidelines. The design standards that are considered in this study are the ACI440.2R-17, CSA-S806.12 (R2017), fib bulletin 90, and TR55. The accuracy of the design models was assessed against an experimental database collected from the literature. The database included RC beams externally strengthened in shear with different FRP types, configurations, and wrapping schemes. In addition, the database included strengthened beams with varying types of anchors. Results showed that most design codes provide reasonable predictions to the FRP shear strength in case of U-wraps. However, the guidelines are significantly conservative in case of complete wraps and anchored specimens. Overall, the ACI440.2R-17 and TR55 predictions are very conservative while fib bulletin 90 and CSA-S806.12 predictions are accurate and can be safely used to design FRP shear strengthened members.