Investigation on the Shear Performance of Concrete Beams Reinforced with Glass Fiber Reinforced Polymer (GFRP) Bars

This paper presents the results of an experimental investigation on the shear behavior of reinforced concrete (RC) beams reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. A total of six (6) RC beam specimens of dimensions 120 mm x 200 mm x 2000 mm were cast, consisting of five (5) full GFRP RC beams and one (1) full steel RC beam. The beams comprised normal concrete of strength of 23.4 N/mm² and 30.4 N/mm², reinforcement of 0.7% and 1.13% GFRP main tensile bars and a constant 0.7% GFRP compression reinforcement. A constant 0.65% shear reinforcement ratio (200 mm GFRP stirrup spacing) and a fixed shear span-to-depth ratio of 3.78 were maintained. The mechanical properties of GFRP and steel bars were evaluated, with nominal diameters of 10 mm for stirrups and 12 mm for longitudinal reinforcement. The investigation sought to evaluate the effects of these test variables on the shear performance of the RC beams subjected to a four-point monotonic loading. Experimental results showed that all GFRP RC beams with a 200 mm stirrup spacing failed in diagonal shear, while the control steel RC beam failed in concrete crushing after yielding of the longitudinal tension steel bars, as predicted by the theoretical analysis. ACI provided conservative shear predictions with an estimated average experimental-to-predicted shear capacity ratio (VExp/VPred) of 1.44, a standard deviation (SD) of 0.17 and a coefficient of variation (COV) of 11.79%. With equivalent test variables, GFRP RC beams exhibited lower shear capacities in comparison to the control steel RC beam due to the reduced dowel action of the GFRP bars and their lower modulus of elasticity, which compromised post-cracking transverse stiffness and shear resistance. The study also examined the impact of strain energy absorption in GFRP RC beams on ductility and energy dissipation in relation to the observed failure modes.