Slip modulus of FRP sheets bonded to concrete

An analytical tension-stiffening model was developed for fiber-reinforced polymer (FRP) sheets bonded to reinforced concrete based on equilibrium equations and the assumption of linear behavior between bond stress and slip. Experimental measurements were made on small- and large-scale specimens. For the small-scale specimens, the primer coat thickness (adhesive thickness between concrete and FRP sheet) was varied for each specimen. By comparisons of the experimental data to the analytical results, the slip modulus at the concrete/FRP sheet and concrete/steel interface was established at the service load level. From this study, it was found that primer coat thickness has a modest influence on the slip modulus of the repaired member, and stiffening of this interface slightly enhances the stiffness of the specimen. After the formation of secondary and diagonal tension cracks, the stiffness of the specimen dropped rapidly and the linearly elastic slip modulus assumption could not be applied. The slip modulus at the concrete/steel rebar interface is less than at the concrete/FRP sheet interface and the slip modulus is independent of the type of FRP sheet.