Development of a simplified bond stress–slip model for bonded FRP–concrete interfaces

An important need in assessing the performance of externally bonded fiber reinforced polymer reinforcement (FRP EBR) for RC structures is to have a constitutive model for the bond stress–slip behavior. Various bond stress–slip models have been proposed and their effectiveness has been verified based on experimental and analytical data. Nevertheless, the models show significant variations and degrees of complexity. In this paper, bond interface modelling of EBR is explored and experimentally supported by double bond testing on 18 test specimens as part of an international Round Robin Testing (iRRT), to investigate the bond mechanisms between FRP reinforcement and concrete. Investigation of the database of models proposed by researchers in literature, shows that often reference is made to the so-called bilinear bond stress–slip model for externally bonded reinforcement. This model is based on three parameters: maximum bond stress, slip at maximum bond stress, and maximum slip. Applicable to this bilinear bond stress–slip model, simplified engineering equations are proposed to define the bond behavior, considering the effect of concrete strength and FRP stiffness on the three parameters identified. The simplified model has been verified against a database of experimental results, showing good correlation (with a coefficient of determination of more than 0.9). It is expected that the model will provide engineers with a basic design guideline to design safe EBR systems, and be a simple model for designing FRP strengthening applications.