## 6 Conclusions  
This paper investigates the effect of the vertical seismic component on the capacity and damage scenario of unreinforced masonry structures. Pushover and nonlinear time history analyses are carried out for a two-story regular wall described with a detailed micro-modelling approach under different dead loads representative of typical stress states. Nonlinear time history analyses (NTHAs) were carried out using three unscaled ground motion records recently recorded in Italy and selected from the ITalian ACcelerometric Archive--ITACA [36]. The records were selected to be spectrum-compatible with the Uniform Hazard Spectrum (UHS) corresponding to a return period TR of 475 years and a rigid soil (cat. A). The recorded ground motions were applied to the case-study structure with and without the vertical component (V) of the seismic acceleration. Two global Engineering Demand Parameters (EDPs) were considered for the NTHA: the Inter-story Drift Ratio (IDR) and the Roof Drift Ratio (RDR), which represent the ratio between the inter-story displacement and the story height and the ratio between the displacement on the top of the structure and its total height. In addition, the behaviour of the single masonry pier varying the vertical load and the IDR of the masonry pier P1 is considered as further EDP. The correlation between the Engineering Demand Parameters (inter-story drift and roof drift ratios) and the Ground Motion Parameters (GMPs) of the horizontal and vertical components was discussed. The influence of the vertical component was highlighted by the apparent correlation between the GMPs of the vertical component and the calculated EDPs. For each step t\({}_{i}\) of the ground motion time histories, the geometrical distance between a given EDP with and without the vertical component was also calculated, and its maximum values (max \(\delta\)) over the entire time history were introduced as a new parameter that was found to be very closely correlated to the GMPs and to the vertical load. This indicates that the vertical ground motion component cannot be a priori neglected for URM walls when moderate-to-large vertical GMPs are expected, as confirmed by a comparison of damage scenarios obtained with and without the vertical component of the earthquake. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**max\(\delta\)**} & \multicolumn{2}{c}{**Record \#1**} & \multicolumn{2}{c}{**Record \#2**} & \multicolumn{3}{c}{**Record \#3**} \\ \cline{2-10}  & **VL-a** & **VL-b** & **VL-c** & **VL-a** & **VL-b** & **VL-c** & **VL-a** & **VL-b** & **VL-c** \\ \hline Max\(\delta\) (IDR\({}_{\text{S1}}\)) & 0.00676 & 0.00710 & 0.01234 & 0.01163 & 0.01254 & 0.02582 & 0.00121 & 0.00114 & 0.00364 \\ Max\(\delta\) (IDR\({}_{\text{S2}}\)) & 0.00319 & 0.00698 & 0.01087 & 0.01623 & 0.01344 & 0.02690 & 0.00057 & 0.00099 & 0.00352 \\ Max\(\delta\) (RDR) & 0.00447 & 0.00632 & 0.01136 & 0.00777 & 0.00939 & 0.02115 & 0.00080 & 0.00081 & 0.00308 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Maximum values of the geometrical distance between the EDPs calculated over each time history with and without the vertical component. Future developments of this work include using additional accelerograms and analysing the role of vertical components of earthquakes for irregular masonry walls and 3D structures, as well as for masonry structures modelled with the equivalent frame approach [41; 42; 43; 44]. Conceptualisation, G.C., A.D.P. and V.S. ; methodology, G.C., A.D.P., V.S. and C.C. ; software, G.C., A.D.P. and C.C. ; validation, G.C., A.D.P., V.S. and C.C. ; writing--original draft preparation, G.C., A.D.P., V.S. and C.C. ; writing--review and editing, G.C., A.D.P., V.S. and C.C. ; visualisation, A.D.P. and C.C. ; and supervision, G.C. and V.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. All relevant data are contained within the article.