Numerical modelling of diagonal compression tests on masonry panels strengthened by FRCM

Fiber Reinforced Cementitious Matrices (FRCM) are innovative materials currently adopted for the structural strengthening of existing masonry structures. With reference to the in-plane behavior of masonry, FRCM systems are effective in enhancing the shear capacity and in influencing the failure mode of masonry panels, which moves from a very brittle failure, typical of unreinforced masonry walls, to a less brittle failure mode. The main objective of this paper is to study the structural behavior of masonry panels strengthened with a FRCM system through nonlinear numerical analyses of diagonal compression tests performed on an unreinforced and a reinforced panel. With reference to the masonry substrate, a brick-to-brick modelling approach is adopted. According to this approach, the non-linearities are all concentrated in the mortar joints and in correspondence with potential crack surfaces located in the middle of each brick. The FRCM strengthening system is discretized by means of a continuous bi-directional fiber grid constituted by trusses embedded into the mortar matrix, which is bonded to the masonry substrate. A calibrated bond-slip relationship is assigned to the matrix-fiber interface, assuming an idealized bilinear law. The nonlinear analyses allow to capture the typical experimental shear response of a reinforced masonry panel, characterized by a load-displacement curve in which three principal phases can be identified, corresponding with different failure mechanisms: masonry cracking, mortar matrix cracking and ultimate failure of the panel. The numerical results are, indeed, compared with experimental results, showing a good agreement and confirming the suitability of the modelling approach in reproducing the described experimental behavior. Parametric studies on both the material and the geometrical parameters of the FRCM system are also performed.