# Integrated Deep Renovation of Existing Buildings with Prefabricated Shell Exoskeleton
## 3 Application to a Real Case Study
### Design of the Holistic Retrofit Intervention
#### 3.2.1 Structural Intervention
\begin{table}
\begin{tabular}{c c c c} \hline
**North and South** & **Element Typology** & \begin{tabular}{c} **Finite Element** \\ **Modeling** \\ \end{tabular} & \begin{tabular}{c} **Description** \\ \end{tabular} \\ \hline Steel Frames & \begin{tabular}{c} Hollow square \\ profiles and plates \\ in mild steel S355 \\ 100 mm \\ structural panels \\ \end{tabular} & \begin{tabular}{c} Elastic beam \\ elements \\ 100 mm \\ structural panels \\ \end{tabular} & \begin{tabular}{c} The steel frames located around the ribbon windows \\ are modeled as 1-dimension elastic beam elements \\ pinned to the RC curbs \\ \end{tabular} \\ \hline CLT panels & \begin{tabular}{c} 100 mm \\ X-LAM \\ structural panels \\ \end{tabular} & \begin{tabular}{c} Plane stress \\ elements \\ \end{tabular} & \begin{tabular}{c} These elements are modeled as 2D plane stress \\ elements fixed to adjacent steel elements \\ \end{tabular} \\ \hline \end{tabular} \begin{tabular}{c} \"Over-resistant\" \\ connections & Steel studs in S355 & \
\begin{tabular}{c} Spring general \\ links \\ \end{tabular} &
\begin{tabular}{c} The \"over-resistant\" connections used to link the \\ shell exoskeleton to the existing building, to the roof \\ and to the foundation system are modeled as \\ elasto-plastic spring general links, described in \\ terms of strength and stiffness \\ \end{tabular} \\ \hline \end{tabular}
\end{table} 
Table 1: Major features of the model for the retrofitted building (Mesh C). Figure 18: FEM model of the retrofitted building (Mesh C) (**left**); examples of ground acceleration (**right bottom**) and drift of the south transversal wall (**right top**). The nonlinear time-history analyses were carried out by considering seven Italian natural accelerograms selected as compliant with the site's elastic spectrum, adopting the Rexel Software [40]. The earthquakes with the maximum peak ground velocity were selected. In the design, the life safety limit state (LSLS, [14]) was considered. Numerical results are summarized in Table 2 in terms of the average of the maximum response of each accelerogram, and an example of drift time history is represented in Figure 18. For all the selected accelerograms, thanks to the activation of the dissipative connections on the short sides of the exoskeleton, the maximum drift was always lower than the considered drift target (equal to 0.5%), which allowed us to maintain the additional steel frame in the elastic range and to limit the damage in the elements of the existing RC frame. In addition, the maximum shear capacity of the existing connections was never reached. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Max Drift**} & \multicolumn{2}{c}{**Plastic Hinge Activation**} \\  & **[\%]** & & \\ \hline Transversal short walls & & & \\ (North and South) & 0.36 & & \\ Longitudinal long walls & & & \\ (East and West) & 0.12 & & \\ Existing Structure & 0.48 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main results of the time history analyses on the retrofitted building (adapted from AdESA 2019).