Flexural performance of concrete beams reinforced with FRP grids

This paper evaluates the flexural performance of simply supported concrete beams subjected to four-point monotonic loading and reinforced with a 2D fiber-reinforced plastic (FRP) grid. The main parameter of the study is the amount of longitudinal FRP reinforcement. With respect to a balanced strain condition, three underreinforced and two overreinforced FRP designs were tested with three identical beams per design. Laboratory recorded load-deflection, failure mode, cracking behavior, and reinforcement strain data are compared with theoretical predictions calculated according to traditional steel-reinforced concrete procedures. The study concludes that, with respect to ACI 318-95, flexural capacity is accurately predicted, but shear strength is not. Deflection compatibility between test results and ACI predictions employing the Branson effective moment of inertia was dependent on the percentage of longitudinal reinforcement. In general, observed flexural stiffness was less than that predicted by Branson's equation. A moment-curvature deflection procedure employing a bilinear concrete model compared very well with measured deflections. Finally, the grid configuration provides an effective force transfer mechanism. Cracking occurred at transverse bar locations only, and FRP tensile rupture was achieved with no observed deterioration in force transfer mechanics.