A fully-analytical approach for modelling the response of FRP plates bonded to a brittle substrate

Composite materials, such as fiber reinforced polymers (FRP), are more and more common as strengthening solution for existing structures. Adhesion between FRP and the existing substrate generally represents one of the main concerns on the effectiveness of these techniques. The bond behaviour of composite materials on concrete substrates (but also steel, masonry and wooden ones) are generally investigated by means of pull-out tests. The present paper, starting from the most common assumptions of the mechanical behaviour of the various materials, proposes a fully-analytical formulation for determining the response in terms of the relationship between the external force and the corresponding maximum interface slip observed in those tests. The proposed approach emphasises the key behavioural differences between “short” and “long” bonding length. The former are characterised by a softening behaviour of the relationship between the applied force and the maximum slip, while the latter exhibits a numerically challenging snap-back behaviour. All the key points of the relationship between the external force and the maximum interface slip are defined in closed-form for both the above mentioned cases. Finally, a comparison with some experimental results obtained on FRP-to-concrete pull-out tests are proposed.