An extended high order cohesive interface approach to the debonding analysis of FRP strengthened beams

• The paper presents a new high order model for the debonding analysis of FRP strengthened beams.
• The model combines cohesive interfaces with an extended high order modeling.
• The analysis considers all stress and stiffness components of the adhesive layer.
• The model considers independent debonding at each physical interface in the layered beam.
• The results provide a high-resolution look into the debonding mechanism and clarify the physical phenomena that govern it.

The paper studies the debonding mechanisms in concrete beams strengthened with externally bonded fiber reinforced polymer (FRP) composite strips. The paper develops a nonlinear analytical model that combines an extended high order multi-layer consideration of the strengthened beam with a cohesive interface modeling of its physical interfaces. The handling of the adhesive layer uses 2D elasticity and considers the layer as an isotropic medium with shear, vertical-normal, and longitudinal-normal stiffness. This allows for capturing the variation of all stress components through the thickness of the adhesive layer and for implementing two distinct cohesive interfaces, one at the adhesive–concrete interface and one at the adhesive–FRP interface. By means of this combination, the model responds automatically with the nucleation and evolution of debonding mechanisms in each physical interface. The study looks into the debonding mechanisms triggered by the localized effects near the edge of the bonded layer and near a flexural crack in the concrete beam. The numerical results, the quantitative comparison with reference results, and the qualitative comparison with experimental observations reported in the literature gain insight into the nucleation and evolution of the failure mechanism. This effort takes another step towards the understanding of the debonding phenomenon and towards the development of a high-resolution analytical platform for its handling.