Modeling the shear behavior of deep beams strengthened with FRP sheets

While external FRP sheets are a viable solution for the strengthening of concrete members, there is a lack of mechanical models that can capture their effect on the shear strength of deep beams. This is in part due to the complex debonding and rupture behavior of FRP, which occurs in parallel with the activation and failure of the other shear mechanisms in deep beams. To address this gap, the current paper proposes a kinematics-based model for the behavior of shear-critical deep beams with externally bonded FRP sheets, including side and U-shape sheets, full wraps and inclined strips. The FRP contribution is modeled as a function of the displacements in the shear cracks by using appropriate constitutive relationships. The model is validated with 20 tests from the literature showing adequate shear strength predictions. Parametric analyses are used to show that the effectiveness of FRP sheets decreases with decreasing shear-span-to-depth ratio and increasing member size. The predictions of the ACI and CNR design equations are also evaluated with the help of the proposed model. While design codes do not account for initial cracks at the time of strengthening, the kinematics-based model is used to simulate this effect by later activation of the FRP.