Effect of FRP stitching anchors on ductile performance of shear-deficient RC beams retrofitted using FRP U-wraps

Premature debonding failure of fiber-reinforced polymer (FRP) composites has remained a problem hindering the efficient utilization of FRP U-wraps. While implementation of end anchorage systems is recommended to overcome this issue, its influence on enhancing the flexural performance of shear-strengthened reinforced concrete (RC) beams has not yet been fully explored. In an attempt to address this, a novel end anchorage system is developed and its efficiency in improving the behavior of shear-strengthened RC beams is evaluated using experiments. The proposed anchorage technique involves an FRP stitching anchor embedded in holes drilled at the end of a groove that is carved out at the terminal point of a U-wrap FRP retrofit along the shear span of the beam. The experimental program is performed using six RC beams, five of which are strengthened with FRP U-wrap shear retrofits. The as-built test specimens are intentionally designed to be shear-deficient prior to the application of FRP composites sheets and that undergo a flexural failure if the FRP shear retrofits used are successful. All the beams are tested monotonically under four-point bending. The results are discussed in terms of load–displacement behavior, ultimate strength, displacement capacity, and ductility factor to show that the proposed anchorage technique is capable of converting the failure mode of the retrofitted specimens from a brittle shear to a ductile flexure-shear one. Finally, the efficiency of the adopted end anchorage system in improving ductility in shear-retrofitted RC beams is explored in detail.