Formulation and validation of a theoretical model for intermediate debonding in FRP-strengthened RC beams

The possible premature failure due to debonding between the adhesive layer and concrete is one of the key issues in FRP-strengthened RC beams; debonding can occur at the beam end (end debonding) or in the cracked zone (intermediate debonding).In the present paper, a mechanical model considering non-linear stress–strain relationships for concrete, steel and FRP-to-concrete interface is presented, with the aim of simulating the behavior of RC beams strengthened by externally bonded FRP plates. The finite element numerical procedure obtained by implementing such a model is also validated by comparisons with available experimental data.Finally, behavioral observations are pointed out, which could be utilized to address the research of simplified formulae for determining the effective value of FRP strain at debonding and enhancing the corresponding proposals in current codes and standards.