Fiber-Reinforced Polymer Shear Strengthening of Short-Span, Precast Channel Beams in Bridge Superstructures

A national study concluded that at least 14 states use precast channel beams for their bridge superstructures. Before the mid-1970s short-span (19-ft) precast channel beam bridges were designed by the Arkansas State Highway and Transportation Department for H15 loading without any provision for shear reinforcement. A recent statewide survey has identified 389 of these bridges that remain in service. About 3% are load posted. Approximately one-third of the 389 bridges are exhibiting deterioration that may be serious. During a recent investigation by the University of Arkansas, 33 precast channel beams were evaluated for structural strength. It was determined that many of these units have inadequate shear capacity. A shear crack frequency distribution curve was developed through examination of the 33 tested beams. A simple shear strengthening technique is presented consisting of fiber-reinforced polymer (FRP) strips as external stirrups. The technique has been developed so that it can be easily implemented in the field. The FRP strips are spaced to prevent the full formation of a diagonal crack between two adjacent strips and designed to ensure a flexural failure rather than a sudden shear failure. Four beams retrofitted with the proposed retrofit technique and two control beams were load tested to failure to evaluate the effectiveness of the technique. Results from the experiment show that the retrofitted beams exhibited at least a 290% increase in deflection ductility and a 418% increase in energy ductility.