## 5 Structural Vulnerability  
In the present section, the results of the structural verification are reported for the steel structures and RC walls. In the case of only gravitational loads, the values of the internal actions and deformations were evaluated by linear static analysis. Conversely, linear dynamic analyses were performed to evaluate the internal actions under seismic actions both for life safety (SLV) and operational (SLO) limit states. Moreover, for steel members, both an evaluation of internal actions and structural verification were carried out by SAP2000. Conversely, for RC cores, the internal actions were evaluated by SAP2000, while structural verification was carried out by the post-processor VIS15 [24] using the plugin SPF (Seismic Performance Finder). The structure was revealed to have barely any criticalities under gravitational loads. Regarding the reinforced concrete elements, verification was carried out according to Section 4.1.2.3 of NTC 2018 [10]. The structure does not present any structural criticality under gravitational loads. Regarding the reinforced concrete elements, verification was carried out according to Section 4.1.2.3 of NTC 2018 [10]. Two failure mechanisms were revealed: (1) combined bending and axial force (FF), and (2) shear failure (SF_w). The whole section of the RC cores was verified under combined bending and compression action, while the shear failure was evaluated for each core wall. The numerical results in terms of the demand-to-capacity ratio (D/C) are reported in Table 8. The work rate of the RC cores under combined bending and axial action is shown in Figure 9a. For the steel elements, structural verification was performed in terms of resistance, stability and deformation. The ultimate resistance of steel members was evaluated according to Section 4.2.4.1 of NTC 2018 [10]. The columns (HEB 260) were verified according to the \begin{table}
\begin{tabular}{c c c c} \hline
**RC Core** & **Story** & **Criterion** & _D/C_ \\ \hline \multirow{2}{*}{T1+T2 (T1\({}^{\prime}\) + T2\({}^{\prime}\))} & 1 st & FF & 0.08 \\  & 4 th & SF\_w & 0.13 \\ \hline \multirow{2}{*}{T3 (T3\({}^{\prime}\))} & 1 st & FF & 0.08 \\  & 5 th–7 th & SF\_w & 0.15 \\ \hline \multirow{2}{*}{T4 (T4\({}^{\prime}\))} & 1 st & FF & 0.11 \\  & 2 nd–4 th & SF\_w & 0.10 \\ \hline \multirow{2}{*}{T5} & 1 st & FF & 0.14 \\  & 4 th & SF\_w & 0.18 \\ \hline \multirow{2}{*}{T6 (T6\({}^{\prime}\))} & 1 st & FF & 0.09 \\  & 2 nd & SF\_w & 0.20 \\ \hline \end{tabular}
\end{table} 
Table 8: Main numerical results of RC cores under vertical actions. Figure 9: Demand-to-capacity ratios for the cores under combined bending and axial force (**a**). Work rates of the steel members under combined bending and axial force (**b**). combined bending-compression action and the buckling resistance under an axial load (N). The beams (IPE 240, HEA 260) were verified against flexural failure (FF) and shear failure (SF) and based on their lateral torsional stability (LT). Moreover, for a simply supported beam, the maximum displacement at the mid-span was computed to check the vertical deflections, according to Section 4.2.4.2.1 of NTC 2018 [10]. The deflection limitation was largely satisfied. Based on ULS, the main numerical results in terms of demand-to-capacity ratio (D/C) are reported in Table 9, while the work rate of steel members is shown in Figure 9b. When reviewing the numerical results, it is possible to conclude that, under gravitational loads alone, there are barely any structural criticalities. Only one column of the central portion of the first story should be strengthened, for which the value of the demand-to-capacity ratio slightly exceeds 1.00 (1.056). Structural verification under seismic action was performed based on the elastic response spectra reported in Section 4.1. Seismic analyses were carried out by preliminarily identifying ductile and brittle mechanisms.