Effect of longitudinal rebar ratio and synthetic fiber dosage on flexure–shear behavior of GFRP-reinforced concrete beams

Abstract

Glass fiber-reinforced polymer (GFRP) bars are increasingly used in construction due to their non-corrosive nature. However, their inherent brittleness affects structural performance. This study examines the flexure–shear behavior of GFRP-reinforced concrete (RC) beams with and without synthetic fibers. Also, their performance is compared with similar Thermo-Mechanically Treated (TMT) RC beams. To ensure meaningful comparison, TMT beams are designed as under-reinforced sections with reinforcement of 0.37%. GFRP beams are designed using two criteria: identical rebar ratio and equivalent flexural rigidity, the latter calculated as (EI)GFRP = (EI)TMT. The effect of discrete polypropylene fiber addition (0%, 0.5%, and 1.0%) is also evaluated. Nine RC beams are tested under flexure–shear loading. Performance is assessed based on load–displacement response, peak load, mid-span deflection, and failure modes. Results indicate that fiber dosage significantly improves strength and post-cracking stiffness. In TMT RC beams, even a nominal 0.5% fiber dosage alters the failure mode. However, GFRP-RC beams show softening of failure with increasing fiber dosage but with no change in failure mode, even at a 1.0% fiber dosage. Interestingly, in GFRP beams with higher rebar ratios, fibers reduce brittleness. The findings highlight the potential of polypropylene fibers in enhancing the ductility of brittle GFRP-RC beams failing in flexure–shear. The flexural and shear capacities of RC beams are predicted by suitably modifying the existing analytical model by RILEM (Réunion Internationale des Laboratoires et Experts des Matériaux, systèmes de construction et ouvrages) [International Union of Laboratories and Experts in Construction Materials, Systems and Structures].