On the Bond Behavior of Anchored FRCM-Reinforced Masonry Pillars Subjected to Direct Shear Tests

In this paper, an experimental campaign carried out on six anchored FRCM-reinforced masonry pillars subjected to direct shear tests is presented. The pillars are built using five bricks separated by one-centimeter-thick joints. FRCM (Fiber Reinforced Cementitious Matrix) reinforcement is applied using PBO (polyparaphenylene benzo bisoxazole) fibers embedded in inorganic matrix layers, a technique chosen for its compatibility with historical masonry constructions. The strengthening system is anchored to the support by means of PBO spikes impregnated into non-organic binders and applied to the central brick. Two technologies are proposed, gripping in the first case the spike to the external matrix layer, and in the second to the fiber. Direct shear tests are performed to investigate the bond behavior between the FRCM and the masonry substrate, as well as to evaluate the contribution of the anchoring devices in improving structural performance. The results, expressed in terms of force-displacement curves, are critically compared with existing studies where no anchoring systems were used, commenting on the role played by the spikes. Furthermore, the study identifies the most effective method for gripping the spikes to optimize the reinforcement system efficiency.