Nonlinear micromechanics-based bond-slip model for FRP/concrete interfaces

Various experimental studies in the literature have reported that the local bond-slip profiles for fibre reinforced polymer (FRP)/concrete joints subjected to direct shear loading and the associated local bond strength values vary along the bonded length. This peculiarity of the local bond-slip curves has apparently not yet been considered in any of the available interface models.In this work, a procedure is developed for deriving a nonlinear bond-slip model for FRP/concrete interfaces that accounts for the variation of local bond strength along the bonded length. The bond-slip law was developed based on 3D nonlinear micromechanics-based finite element results using the microplane theory for concrete. In the finite element analysis, the microplane constitutive law is implemented as a user-defined subroutine in the ADINA finite element package to run the simulations. Subsequently, the finite element results have been used to develop the nonlinear bond-slip constitutive law for the FRP/concrete joints. This constitutive relation is developed considering the interaction between the interfacial normal stress components along the bonded length and local bond strength. Then a new mathematical approach is proposed to describe the entire local bond-slip relationship. The proposed interface law accounts for the nonlinear contributions of the FRP laminates, adhesive and concrete layers.Finally, to assess the efficacy of the proposed bond-slip model, validations are carried out using a large experimental database (results of 118 specimens). The predicted ultimate load carrying capacities show a satisfactory agreement with the test data. Furthermore, comparisons are made among the characteristics and predictions of the proposed model and those of two bond-slip models from the literature.