# 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
The reduced number and dimensions of the micro-piles provide evidence for the effectiveness of the shell structure in exploiting the extension of the facades to increase the lever arm and to reduce the magnitude of the vertical forces balancing the bending moment at the base level. The new foundation curb was stud-connected (\(\phi\)22 mm/100 cm) to the existing base RC slab and foundations to increase resistance against shear-sliding at the base. As for the three typologies of structural connections, over-resistant stud connections (\(\phi\)22 mm/50 cm) were adopted to fix the walls to the existing floor and roof diaphragms (details 1 and 2 of Figure 13) and to connect the exoskeleton to the foundations (detail 4 of Figure 13). On the other hand, different elements of the shell exoskeleton, i.e., CLT panels and steel frames, were connected either with over-resistant connections (thin steel plates, with a thickness of 4 mm, nailed to timber panels and welded to box-steel profiles) or with dissipative connections similar to the ones in Figure 4 (right), aimed at dissipating energy and limiting the loads induced by earthquakes (detail 3 of Figure 13). These particular connections were conceived, tested, and placed along the short sides, in order to amass the most possible damage in case of high-intensity earthquakes and enable activating a ductile mechanism at CLS. These connections are composed of an array of steel plates (s = 8 mm, h = 100 mm, b = 100 mm, 300 mm spacing), subjected to out-of-plane bending, and are conceived as a way to cap the seismic action (F\({}_{y,\text{cap}}\) = 12 KN), thereby maintaining the panels and steel frames in the elastic field (Figure 14). The dissipative device was nailed to the CLT panel (\(\phi\)4/50 mm) and welded to the steel frame to transfer the shear flow. Figure 14 shows the setup of the cyclic tests carried out at the University of Bergamo and the obtained hysteretic loop of the connection, as well as the dissipative connections after their assemblage on-site. Finally, mechanical anchors were adopted to constrain the CLT panels and the steel frames against out-of-plane loading (Figure 13b). Figure 12: Roof diaphragm: concept (**left**) and realization before the introduction of the L-shaped steel elements (**right**). In Figure 13b, the elevation of the southern facade is reported before (left) and after (right) the structural intervention. In Figure 13b (left), it is possible to distinguish the CLT panels (in orange), the steel frames (in dark grey), the connection to the roof and to the intermediate diaphragms (rectangular plates), the dissipative connections located between the steel frame at the ground floor and the intermediate wooden panels (array of vertical steel plates), and the new foundation system (curb--in a diagonal square pattern--and micropile at the building corner). Pictures of the construction stage of the prefabricated CLT panels are shown in Figure 15.  
Figure 13: Structural intervention along the short facades of the building: (**a**) structural scheme; (**b**) section, front view and details (all measures in centimeters). Along the long side of the building, the seismic-resistant facades were obtained from exploiting and re-engineering the existing elements, thus avoiding the introduction of the CLT structural layer. To increase the in-plane stiffness and strength of the LFRS, mechanical connections made of 10 mm steel plates and \(\phi\)20 studs, 8 on each vertical element, were introduced between adjacent cladding panels to enforce the coupling of the panels. The elements of the connection system were designed according to the simplified structural scheme of Figure 16 (top) and were then verified in the global model of the retrofitted building. The structural facade was connected with \(\phi\)22/50 cm study to the roof diaphragm and to the existing foundation, to transfer shear flow.