## 6 Conclusions  
The paper is focused on the assessment of the shear capacity of un-strengthened and in-plane FRCM-strengthened masonry walls under diagonal compression force. Previous numerical analyses carried out by means of a Finite Element (FE) Model simulating diagonal compression tests were used in the paper in order to calculate the shear strength starting from the values of the maximum diagonal compression forces. To this aim, various approaches commonly adopted for the interpretation of diagonal compression tests in terms of shear force were examined. Due to the simplicity of the set-up, several experimental and numerical results of diagonal compression tests are, indeed, available in literature. Conversely, since codes and literature provisions for the strength capacity of masonry walls are given in terms of maximum shear force, the paper aimed to compare such theoretical values with the numerical results of diagonal compression tests and to find the most suitable approach for interpreting the results of this type of test both for the un-strengthened and the FRCM-strengthened \begin{table}
\begin{tabular}{l l c c c c} \hline \hline \multirow{2}{*}{**Approaches**} & \multirow{2}{*}{**Shear Force**} & \multicolumn{5}{c}{**Parameters**} \\ \cline{3-6}  & & **MAPE** & **MSE** & \(\mathbf{R}^{2}\) & \(\beta\) \\ \hline Approach 1 & \(V_{t}=0.71\,P\) & 0.51 & 15463 & 0.60 & 0.50 \\ Approach 2 & \(V_{t}=0.88\,P\) & 0.61 & 32894 & 0.60 & 0.40 \\ Approach 3 & \(V_{t}=0.50\,P\) & 0.30 & 2702 & 0.60 & 0.75 \\ Approach 4 & \(V_{t}=0.33\,P\) & 0.26 & 1585 & 0.6 & 1.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistical error indicators for the different approaches applied to the strengthened walls—procedure “A”. \begin{table}
\begin{tabular}{l l c c c c} \hline \hline \multirow{2}{*}{**Approaches**} & \multirow{2}{*}{**Shear Force**} & \multicolumn{5}{c}{**Parameters**} \\ \cline{3-5}  & & **MAPE** & **MSE** & \(\mathbf{R}^{2}\) & \(\beta\) \\ \hline Approach 1 & \(V_{t}=0.71\,P\) & 0.35 & 9464 & 0.52 & 0.62 \\ Approach 2 & \(V_{t}=0.88\,P\) & 0.47 & 23802 & 0.52 & 0.50 \\ Approach 3 & \(V_{t}=0.50\,P\) & 0.22 & 1414 & 0.52 & 0.93 \\ Approach 4 & \(V_{t}=0.33\,P\) & 0.43 & 2273 & 0.52 & 1.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Statistical error indicators for the different approaches applied to the strengthened walls—procedure “B”. walls. The comparisons were based on the assumption that numerical results from validated models are equivalent to experimental ones, since several studies are already available in literature on the reliability of FE models to correctly predict the experimental outcomes. The indication of Italian codes both for un-strengthened (IBC, 2018 [35]) and strengthened walls (CNR DT 215, 2018 [26]) were considered as reference for the comparisons. For all the considered cases, the comparisons show that the approach assuming the shear force equal to half of the maximum diagonal compression force seems to be the most suitable. According to this approach, the theoretical values are indeed lower than the FEM predictions with a reasonable safety. This argument is based on the assumption that the results of validated FE models, i.e., numerical experiments, are considered equivalent to experimental tests; thus, the theoretical values should be equal to the FE predictions. In this sense, the theoretical values are not \"safe\" from a design point of view, but by looking at the predictability of the numerical results. For the strengthened walls, a detailed analysis of the actual strain levels in the reinforcement when the strengthened walls fail was carried out, too, by means of a deep analysis of the numerical results. According to the CNR guidelines for design of interventions with FRCM materials, a conventional strain for the fibers has to be used for assessing the shear strength of the strengthened wall. To date, such a conventional strain should be assessed by means of bond tests.