Modified Shear Design Model for Steel- and Fiber-Reinforced Polymer-Reinforced Concrete Beams

This study proposes a unified shear design provision for slender steel- and fiber -reinforced polymer (FRP)-reinforced concrete (RC) members. The proposed model is a modification of the ACI 318-19 model to include the axial stiffness of the longitudinal reinforcement by introducing a new modification term, nc, representing the elastic modular ratio of the longitudinal reinforcement to the concrete. The new relation is V-c = (0.4 [n(c)rho(fl)](1/3) lambda(s)root f(c)' + N-u/[6Ag])b(w)d. The unified shear model was assessed with five experimental data sets: FRP-RC beams without shear reinforcement (288 beams), steel -RC beams without shear reinforcement (759 beams), FRP-RC beams with shear reinforcement (56 beams), steel -RC beams with shear reinforcement (157 beams), and steel -RC beams with axial force (prestressed) but without shear reinforcement (209 beams). The unified shear model provided better performance than the ACI 318-19 and ACI CODE -440.11-22 provisions in terms of mean, coefficient of variation, standard deviation (SD), and absolute average error (AAE). The unified model also showed improved performance over a wider range of material properties. In addition, reliability analysis using Monte Carlo simulation indicated that the unified shear model provides a consistent satisfactory safety level with a reliability index between 3.5 and 4.0 for both steel- and FRP-RC members. The reliability index provided by the unified model is similar to the reliability index provided by the ACI 318-19 shear provision. In contrast, the ACI CODE -440.11-22 results in highly conservative estimates with a reliability index between 4.5 and 5.0.