Interface bond between FRP sheets and concrete substrates: properties, numerical modeling and roles in member behaviour

The success of most of strengthening or retrofitting technologies for concrete structures by using external bonded FRP sheets depends highly on the interface bond between the FRP sheets and concrete substrates. This paper reviews current studies on evaluating the bond properties of FRP sheet–concrete interfaces and, in particular, focuses on several newly developed bond models for describing the bond characteristics of FRP sheet–concrete interfaces under various loading conditions. This paper also gives several examples that apply these interfacial bond models to the design of different retrofitting cases. Analytical solutions are discussed that consider the local interfacial delamination and slip behaviour, which can improve the prediction of strength and deformation performances, as well as clarify the failure mechanisms of concrete members upgraded with FRP composites. Moreover, the improvement in structural performance of retrofitted concrete members is discussed by relating them to the optimum microscopic properties of the interface bond and the properties of retrofitting materials.