Few design oriented models on strengthening of unreinforced masonry (URM) panels under in-plane actions with composite systems are currently available (among them, the pioneers researches [1, 2] and the guidelines [3, 4] for FRPs). Usually, the in-plane shear capacity of a strengthened panel is evaluated as the sum of two terms: the contribution of URM masonry and that of the composite strengthening system (usually only the fibers are considered, also in the case of inorganic matrix, as illustrated in [5, 6, 7], neglecting the shear contribution of the matrix). Mostly, the models proposed to compute the strength increment of the URM can be seen as extensions of provisions for steel-reinforced masonry, where the reinforcement is modeled by the truss analogy [8] and an effective ultimate strain is introduced to account for premature failure of fibers in shear applications. However, the development of the ideal truss in a masonry wall is strongly conditioned by a proper anchorage of fibers and availability of a fiber grid, which is not always ensured. Several failure modes can be expected for strengthened masonry, like diagonal splitting cracking, sliding of a portion over the other, so that the contribution of the composite can be engaged in different ways. The aim of this study is to compare different modeling strategies in the numerical field accounting for matrix as a continuum or as a stiffening of individual fibers, and to provide novel FEM analyses revealing the different role of fiber orientations and matrix properties.
In-plane Shear Strengthening of Unreinforced Masonry Walls Using GFRP Jacketing