# Integrated Deep Renovation of Existing Buildings with Prefabricated Shell Exoskeleton
## 3 Application to a Real Case Study
### Existing Building Performances in the As-Is Condition
In order to assess the structural and seismic vulnerabilities of the case-study building, two different 3D nonlinear models of the structure were assembled (Figure 9, herein referred to as \"Mesh A\" and \"Mesh B\"), and pushover analyses were carried out, adopting the software Midas Gen (2020) [34]. In Mesh A, only the main structural components (columns with isostatic beams) were modeled, while the secondary elements were considered only in terms of masses; in Mesh B, the precast cladding panels (modeled as beam elements) were also introduced, with their connections to the frame structure (modeled as general links with elasto-plastic behavior), considering their effective number, position, stiffness, and strength (more about the connections may be found in [16; 35]). In both models, the roof precast double tees were modeled with truss elements linked to the edge beams; no roof diaphragm action can be attained in the as-is condition given the poor detailing and the lack of either double-tees mutual connections or errados topping. On the other hand, the intermediate floor was modeled with plate elements to simulate its effective in-plane stiffness, enabled by the cast in situ topping. The possible interaction of the staircase, constrained to a perimeter column at the middle height, was also considered by introducing an absolute constraint to the horizontal translation at that point. As for the boundary conditions, columns were modeled as fixed to the ground, whereas cladding panels were modeled as pinned. Precast beams were modeled as single-bay elements, pinned to the columns. As expected, comparative analysis of the structural responses obtained from the two models allowed us to evaluate the difference in terms of stiffness, deformability, and vulnerability of the two structural layouts, highlighting the contribution of the cladding panels to the structural behavior against horizontal loads, which could not be neglected. A comparison of the building capacity and the seismic demand (\(d^{*}\,SLV\)) is reported in Figure 10, both considering (Mesh B) and disregarding (Mesh A) the precast cladding panels. In Mesh A, diffuse plasticization of the columns can be observed, until the ultimate bending deformation of the elements on the north facade is reached. These elements are indeed subject to greater deformations due to the torsional behavior induced by the in-plan and in-elevation irregularity of the building. The displacement capacity of the building is compatible with the demand at LSLS in Mesh A, in which only the main frame elements, characterized by high deformability capacity, were considered. However, this deformability is not compatible with that offered by the stiffer elements, such as cladding panels. In Mesh B, the presence of the cladding panels with rigid connections leads to the premature  
Figure 9: The 3D nonlinear models of the structure in the as-is condition: Mesh A, without cladding panels (**left**) and Mesh B, with cladding panels (**right**). failure of the connections on the north side, followed by the overturning of the cladding panels), with a significant loss of stiffness for the structure. After this point (dashed line), the capacity curve continues with the yielding of the columns and the attainment of the ultimate bending capacity of the elements on the first floor on the south side. However, the dashed portion of the curve has only a numerical meaning since the capacity of the building is considered as being limited to the point of the curve where the cladding panels connections fail. The displacement demand for LLS is thus not satisfied, resulting in a safety index for the building in the as-is condition that is equal to 0.14. From an energy point of view, the main deficiencies of the building were identified by analyzing its envelope, its plants, and the management of the building in terms of heating/cooling and air ventilation.