Shear behaviour of RC structural members strengthened with FRP materials: a three dimensional numerical approach

Structural behavior of Reinforced Concrete (RC) beams strengthened in shear by means of Fiber Reinforced Polymer (FRP) sheets is a very complex subject actually under discussion. A number of experimental programs have shown the importance of the FRP debonding/peeling failure and the mutual interaction between the existing steel web reinforcement and the external FRP sheets/laminates for the evaluation of the whole shear capacity of the structural element. In this work a three dimensional numerical Finite Element procedure, accounting for Mazars’ damage law, included in a contact algorithm, to model the mechanisms at the FRP-concrete interface, was implemented to catch the global failure mechanisms that characterize the ultimate shear capacity of RC members with transverse steel reinforcement and FRP strengthening. The study is based on the experimental tests, described in Pellegrino and Modena (2002), carried out on RC beams with transverse steel reinforcement with and without FRP shear strengthening. It has been shown that the numerical approach is able to describe the experimental behavior of the structural member taking into account the interaction between concrete, steel and FRP contributions to shear capacity and, in particular, how the presence of external FRP sheets can modify steel contribution to the ultimate shear strength of the beams when FRP debonding/peeling failure occurs.