Effect of Macrosynthetic and Hybrid Fibers on Shear Behavior of Concrete Beams Reinforced with GFRP Bars

Design of reinforced concrete (RC) bridge members with fiber-reinforced polymer (FRP) bars as internal reinforcement are usually governed by their serviceability parameters, such as crack width and deflection. This study investigates the effect of structural fibers on the shear behavior of RC beams with glass fiber-reinforced polymer (GFRP) rebar as longitudinal reinforcement. The objective of this study is to understand the efficiency of macrosynthetic polyolefin (PO) polymer and a hybrid combination of steel and PO fibers in improving the shear behavior of GFRP-reinforced beams. In total, 13 full-scale RC beams are cast with GFRP rebars as internal reinforcement and varying PO and hybrid fiber dosages. Three different fiber dosages by volume of concrete (v(f)), namely 0.35%, 0.70%, and 1.0% are considered. The beams are tested under three-point bending configuration with a shear span (a) to effective depth (d) ratio of 2.2 to simulate shear dominant behavior. Experimental results revealed that the addition of fibers increased the postcracking stiffness, peak load, and ductility when compared with control beams with no fibers. Soon after cracking, an excessive load drop in the control specimen is observed due to the low elastic modulus of GFRP rebars. The addition of PO and hybrid fibers reduced the load drop significantly and enhanced the postcracking performance by improving the aggregate interlock and through reduction of residual tensile stresses at the crack tip. The angle of the crack increased with an increase in fiber dosages, indicating the change of the failure mode from brittle shear tension to ductile flexure at higher fiber dosages (0.7% and 1.0%). The shear strength predictions obtained from ACI and RILEM recommendations are found to be very conservative when compared with the test results.