Debonding of FRP in bending: Simplified model and experimental validation

Reinforced concrete members strengthened in bending by bonding of surface-mounted fiber-reinforced polymer (FRP) may present several failure modes: failure of material (reinforcing steel, concrete and composite material) or failure of the interface between concrete-adhesive or adhesive-FRP. Nevertheless, experience gained from testing confirms that in most cases delamination prevails over the other possible rupture modes. Delamination in FRP strengthened sections is difficult to model because it involves multiple parameters such as FRP stiffness, adhesive material properties, presence of cracks in concrete, among others. A simplified model to predict strain of FRP at failure is presented in this paper. The experimental validation is presented as well. With this purpose carbon FRP and aramid strengthened specimens and large scale bridge models are considered. The types of bridge models tested include externally-prestressed segmental box-girder and monolithic RC continuous girders.Based on the results of the proposed model, an equation for the prediction of the ultimate force per unit width in the FRP to prevent FRP debonding is proposed. The equation has been experimentally checked with beams of small and large size, representative of real structures. In comparison to other available models, the equation is very simple to apply.