Assessment of the FRCM in-plane behavior in masonry retrofit applications

Because of its well-documented effectiveness in enhancing the strength and ductility of unreinforced masonry (URM) construction, Fiber Reinforced Mortar (FRCM) is now widely used for the consolidation of heritages, such as churches, palaces, castles, and entirely historical centers. The main purpose of this work is to provide the authors' principal outcomes in the FRCM application to masonry after performing extensive experimental campaigns and numerical simulations over the previous few years. The recent findings have already been appreciated by the research community but have yet to be considered in existing standard codes/recommendations, leaving the contribution of fiber mesh (i) and features of both coating mortar and URM wall (ii) to the improvement of the shear strength of reinforced masonry panels unclear. In fact, unlike FRP, fibers embedded in the mortar coating of the FRCM do not affect the shear strength of the reinforced panel, "limiting" its effect in enhancing the load-bearing capacity of the wall and, therefore, the structure's ductility. This important recent experimental/numerical evidence should be incorporated into the code's recommendation to avoid overestimating the FRCM performance during design phases. Furthermore, the Italian codes suggest simplified amplification factors for estimating the improvement of shear strength owing to the strengthening system that ignores the fact that the greater the thickness of the masonry wall, the lower the FRCM's efficiency, and vice versa. A practice-oriented analytical formulation has been provided to validate such mechanisms by confirming a consistent data set of masonry panels strengthened by FRCM tested under diagonal compression. In this work, a numerical investigation is provided to highlight the importance of considering the effective thickness- and tensile strength-ratio between the FRCM mortar coating and the URM panel to accurately predict the enhancement in the mechanical behaviour of the FRCM-reinforced masonry.