Empirical FRP-concrete effective bond length model for externally bonded reinforcement on the grooves

The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) off the concrete substrate in retrofitted structures. In FRP application, the effective bond length is defined as a length over which the majority of the bond stress is transferred and the maximum load-bearing capacity is obtained. The present study endeavors to develop an original empirical model of the effective bond length of FRP sheets applied on concrete via the EBROG technique. For this purpose, an experimental program is conducted in which 95 specimens prepared through the EBROG and EBR techniques are subjected to the single lap-shear test. The effective bond length is evaluated by analyzing the strain and stress fields on the FRP bond area using the image processing technique of particle image velocimetry (PIV). A model is then developed based on a nonlinear regression analysis along with a probability study performed on the results obtained from the experiments; and the goodness of fit to the data is confirmed. In this model, the effects of groove dimensions, concrete compressive strength, as well as FRP sheet width and stiffness are taken into account. The feasibility of the well-known existing models developed for EBR method was investigated in the EBROG technique and the prediction accuracy was compared with the proposed model.