Out-of-plane strength of brick masonry retrofitted with horizontal NSM CFRP strips

The magnitude of damage possible in unreinforced brick masonry construction subjected to high levels of out-of-plane loading is well understood. Due to the large global building stock of masonry structures, it is essential that efficient retrofitting techniques be developed. The use of fibre-reinforced polymer (FRP) strips has been shown to improve the load-carrying and displacement capacities of masonry sections subjected to out-of-plane loading. This paper presents the results of an experimental and theoretical investigation into the behaviour of modern clay brick masonry retrofitted with horizontally oriented FRP strips subjected to horizontal bending. Experimental tests were conducted on four masonry wallettes retrofitted with horizontal near-surface mounted (NSM) carbon FRP strips, subjected to horizontal bending. The specimens were tested in a vertical orientation with variation in vertical compressive loading. The application of compressive load improved the FRP confinement efficiency, and thus increased the maximum strength of the specimens. The primary failure modes were displacement induced (DI) debonding and FRP buckling. Mathematical models were developed to predict the moment at cracking and moment capacity for the specimens. The models explicitly account for the flexural strengths of the mortar and brick units, the torsional resistance of the bed joints, the NSM FRP, as well as the contributions to bed joint shear strength from the vertical compressive stress and friction. The proposed mathematical models were validated against the results of the experimental tests.