Modeling of shear behavior of reinforced concrete beams strengthened with FRP

The response behavior of shear critical reinforced concrete beams was large investigated, and many studies were presented in literature. However, several issues, like the strain level of FRP at the shear failure, and the interaction between internal and external reinforcement, remain not completely understood. This paper presents an analytical model for the response behavior of reinforced concrete beams strengthened in shear with FRP. The proposed procedure has been based on the Modified Compression Field Theory and can reproduce the whole load-displacement curve. The stress and strain fields have been rigorously calculated for each load step. The effective failure strain of FRP reinforcement has been investigated by applying two different approaches. The reduction of the stirrups stress level in the presence of the external composite reinforcement has been alternately both neglected and taken into account, thus to obtain a comparison of the numerical predictions. The accuracy of the proposed model has been assessed using a database of 71 specimens reinforced with FRP. The results have showed that the proposed model has yielded accurate results and the influence of key parameters on the predictions has been highlighted. Furthermore, a simplified formulation for the evaluation of the shear strength has been derived.