Assessment of a bond strength model for FRP reinforcement externally bonded over masonry blocks

According to recent design Codes and Recommendations, verification against debonding is imperative in the design of strengthening interventions with Fiber Reinforced Polymers (FRP). In FRP - reinforced masonry elements, debonding at reinforcement extremities (end debonding) must be avoided by limiting the maximum force achievable by the strengthening system. This paper proposes design criteria against debonding in masonry elements externally strengthened by FRP sheets. Results of more than 250 bond tests, reported in the literature and carried out over different masonry supports, clay bricks and natural stones, are collected and examined. Formulas for fracture energy of interface bond law and debonding load are assessed starting from the experimental database. In order to provide design formulas according to the Partial Safety Factor Method for Ultimate Limit State verification, mean and characteristic values of the debonding load are determined through statistical methods.