## Code Provisions for Shear Strength of In-Plane FRCM Strengthened Masonry Panels  
According to the novel Italian guidelines for strengthening with FRCM materials (CNR DT 215 2018 [26]), the capacity of the strengthened walls with FRCM composite material can be evaluated as the sum of two contributions ([PERSON] et al., 2018 [34]): the shear strength of the un-strengthened walls, \(V_{t}\), evaluated according to the current Italian code (IBC, 2018 [35], IBCC, 2019 [36]) for un-strengthened walls in case of \"diagonal cracking\" failure, plus the strength contribution of the composite, \(V_{t,f}\), computed according to the following formulation:  
\[V_{t,f}=\frac{n_{f}\cdot t_{Vf}\cdot\ell_{f}\cdot\alpha_{t}\cdot\varepsilon_{ fd}\cdot E_{f}}{2}, \tag{1}\]  
where 2 is a safety factor related to the calculation of a design value, \(n_{f}\) is the total number of reinforcement layers placed on the two sides of the wall, \(t_{Vf}\) is the equivalent thickness of a single reinforcement layer with fibers arranged along the direction parallel to the shear force, \(\ell_{f}\) is the size of the strengthening system measured orthogonally to the shear force--and, in any cases, it cannot be greater than the width of the wall \(l\) (dimension measured parallel to the shear force)--, \(\alpha_{t}\) is a parameter that takes into account the reduced exploitation of the fibers when stressed in shear (0.8 is the suggested value lacking experimental information), and \(\varepsilon_{fd}\) is the design value of the maximum strain of the fibers that can be assumed equal to a conventional strain evaluated as:  
\[\varepsilon_{f,d}=\frac{\sigma_{lim,conv}}{E_{f}} \tag{2}\]  
with \(E_{f}\) being the Young's modulus of the dry fibers. The conventional tensile stress, \(\sigma_{lim,conv}\), should be evaluated according to bond tests carried out on the FRCM system bonded on a specific masonry substrate and could be further increased by a factor \(\alpha\), variable in the range 1.0-1.5, if the failure mode does not involve an anchorage zone of the reinforcement. Moreover, the value of \(\sigma_{lim,conv}\) cannot be higher than the tensile strength of the fibers, evaluated by means of tensile tests on FRCM coupons ([PERSON] et al., 2018 [37]). It is worthy of note that, in several experimental programs concerning tests on masonry walls ([PERSON] et al., 2019 [38], [PERSON] et al., 2018 [39], [PERSON] et al., 2019 [40]), no bond tests are performed on the same strengthening material; this means that it is not possible to compare the maximum tensile strain attained in the FRCM reinforcement when applied on the walls with the values provided by bond tests on the same type of reinforcement and masonry and thus assess the conventional strain or stress. Consequently, some uncertainness about the assessment of the conventional tensile strain or stress in the FRCM reinforcement does exist. To fill this gap, in Section 5.2, some considerations about the assessment of the strain levels in the FRCM reinforcement when the walls fail will be carried out. On the behavior of un-strengthened masonry walls, the simplified models available in the scientific literature and in several national codes are intended to describe the different failure modes that can occur in masonry walls when subjected to in-plane horizontal forces, such as flexural or shear failures. With reference to shear failures, two main types of behavior can be detected in masonry walls: (1) shear failure for sliding along the mortar joints, typical of regular masonry and usually predicted by the Mohr-Coulomb criterion, and (2) diagonal cracking failure. The latter can occur according to further modalities: (2a) failure in the mortar joints, mainly typical of regular wall texture, and (2b) cracks intersecting the units, typical of irregular masonry texture.