Debonding resistance of FRP-to-clay brick masonry joints

Debonding at the FRP-to-masonry interface has been identified as the preferred failure mechanism in fibre-reinforced polymer (FRP) retrofitted masonry as it allows for some redistribution of forces. The results of 14 FRP-to-masonry bond tests are presented, where the FRP was near surface mounted (NSM) to stack-bonded clay brick masonry. These tests were conducted to investigate the effect that variables such as cyclic loading and FRP strip dimensions have on the debonding resistance of a NSM FRP-to-masonry joint. These results were then incorporated into a large database of FRP retrofitted masonry pull test results by various researchers over the past 10 years. The database includes results for both externally bonded (EB) and NSM retrofitting techniques. From this database, local bond–slip parameters such as the maximum interface shear stress, τmax, and the maximum slip, δmax, were investigated to determine correlations between these values and masonry material properties. Further, 15 existing concrete and masonry bond strength (maximum load at the FRP-to-substrate interface) models in the literature were assessed for their use with masonry by comparing these models against the results in the pull test database. Based on the comparative statistics of the test-to-predicted bond strength it is concluded that a new FRP-to-masonry bond model is required which gives more accurate predictions. Results include a discussion on the global load–slip response and FRP-to-masonry interface behaviour