Analytical model for shear strength of FRP-reinforced RC beams: influence of lever arm evaluation

Many reinforced concrete (RC) structures do not meet modern seismic standards and require strengthening interventions. Shear strengthening of RC beams using fiber reinforced polymer (FRP) composites is a widely adopted retrofit technique. The shear strength of FRP-retrofitted RC beams is influenced by brittle failure modes that reduce the effectiveness of FRP reinforcement. Analytical models account for this using an effectiveness factor "R" to lower the FRP's tensile strength. Brittle FRP failure also reduces the shear contribution of steel stirrups due to hindered yielding, addressed by an additional factor "r." Moreover, the evaluation of lever arm can influence the calculation of theoretical shear strength of reinforced concrete beams strengthened with FRP. This study examines the impact of R factor and lever arm evaluation in a shear model previously developed by the Authors. The reliability of theoretical predictions is analysed by comparison with databases with different reinforcement arrangements.