Shear Strength of FRP Reinforced Concrete Beams without Stirrups: Verification of Fracture Mechanics Formulation

The size effect in shear in reinforced concrete (RC) one-way members without shear reinforcement becomes more of concern when using glass fiber reinforced polymer (GFRP) reinforcement. In fact, the lower axial stiffness of GFRP reinforcement typically results in wider flexural cracks with respect to steel RC counterparts. This issue is especially relevant for the case of flexural members without stirrups, such as retaining walls and slab bridge superstructures. Little evidence has documented the extent of such effect. Cognizant of this knowledge gap, ACI Committee 440 (FRP Reinforcement) introduced the current nominal shear strength algorithm, which was calibrated in a conservative fashion based on test results from small beams. This algorithm assumes that the shear strength at the critical section is resisted predominantly through the uncracked concrete above the tip of the shear crack. Based on the same fundamental assumption, a fracture mechanics algorithm for steel RC beams was recently proposed by ACI Committee 446 (Fracture Mechanics of Concrete). In this paper, the ACI 440 and 446 algorithms are verified and discussed based on experimental evidence from tests on scaled GFRP RC beams without stirrups. The latter algorithm is modified to account for the smaller elastic modulus of GFRP, under the hypothesis that its relevant parameters and the shear failure mechanism are similar irrespective of the reinforcement material.