Presented in this paper is a coupled damage model to predict the durability of concrete elements strengthened by external bonding of fiber reinforced polymer (FRP) plates. Both the concrete, the strengthening FRP and the glue are modeled as damageable materials. The damage model is developed within the framework of the principle of virtual power. The adopted power of the internal forces depends on the damage velocity and on its gradient to take into account local interactions. An interaction between the domain damage and the damage along the interface is introduced. Preliminary comparison between numerical results and experimental tests are proposed showing that the model captures well the debonding fracture initiation, and provides an accurate description of the rupture mode.