The influence of the load condition on the intermediate debonding failure of EBR-FRP strengthened RC beams

Intermediate debonding is one of the most common and peculiar bond-related failure modes observed in RC beams externally strengthened in bending by bonded FRP reinforcement. This paper firstly presents some general behavioral observations derived by previous studies based on utilizing a numerical procedure implemented and validated by the authors. In particular, the correlations between the amount of steel rebars (or yielding stress) and intermediate debonding failure are outlined and the effect of the load condition on the value of FRP strain at debonding is argued by some experimental results given in literature. Looking after the key mechanical parameters controlling the bond behavior, a formula for intermediate debonding failure is derived through a design-by-testing procedure based on a wide collection of experimental results. The model uncertainties are handled through a consistent statistical procedure leading to a sound definition of the characteristic value of the relevant design quantities. Finally, the formula is refined based on the results of the aforementioned numerical procedure to take into account the effect of load condition. Further experimental results could increase the trust in predictions less conservative.