Experimental Investigation of Concrete Beams Reinforced with Glass Fiber-Reinforced Polymer Bars

Concrete beams reinforced in shear and flexure with linear elastic and brittle glass fiber-reinforced polymer (GFRP) bars show differences in behavior when compared with the traditional steel-reinforced concrete beams. The flexural design of these beams follows similar principles as the design of steel-reinforced concrete members, except that the cross section is over-reinforced to compensate for the lack of reinforcement ductility. GFRP-reinforced beams are designed in shear using semiempirical modifications to the design equations for steel-reinforced concrete. The modified equations have not been well studied for beams with high shear span to depth (a/d) ratios. The presented research program is composed of three-point bending tests of ten GFRP-reinforced concrete beams, with a/d slenderness ratios from 4.5 to 10.5 with constant flexural reinforcement and varied shear reinforcing. The observed mode of failure transitioned from shear to flexure-controlled with increasing specimen slenderness and increased shear reinforcing. All failures were controlled by concrete behavior, either in tension for beams without shear reinforcement or compression for beams with shear reinforcement. The inclusion of GFRP stirrups in the beams prevented brittle failures by providing confinement to concrete. Comparisons with the current design rules showed good agreement with experimental results. However, the relative contribution of concrete and reinforcement to shear-carrying capacities differed in the code predictions from results derived from measured strains.