# Integrated Deep Renovation of Existing Buildings with Prefabricated Shell Exoskeleton
## 2 AdESA System: An Anti-Seismic, Eco-Efficient Wooden Shell
### Structural Layer  
From a structural point of view, exoskeletons may be designed by adopting two different structural schemes: the wall solution, which amasses the stiffness and resistance of the lateral force-resisting system (LFRS) into a number of discrete additional elements, and the shell solution, which exploits the extension of the building facades to reduce the thickness of the LFRS [27]. Both solutions require floor diaphragms to collect and transfer the seismic actions to structural exoskeletons. The need for floor diaphragms can be an issue if the existing floors were not engineered against seismic actions, especially in shell solutions, which require a higher capacity of the floors, provided that the spacing between the vertical element of the LFRS is generally larger than in the wall solution [28]. Accordingly, when designing new exoskeletons, particularly in the case of shell systems, the in-plane capacity of the existing floors and roof must be preliminarily assessed and possible reinforcements must be designed. The structural conceptual design of the AdESA system entails a shell exoskeleton to be placed either in close proximity to or with an offset with respect to the building facade. The seismic-resistant layer of the AdESA system is composed of an outer wooden box structure made of CLT panels along the perimeter facades (arranged either horizontally, spanning between two adjacent floors, or vertically, spanning from ground to roof), a roof diaphragm, realized either by exploiting the existing roof or by adding new plywood panels mutually connected with nailed steel flanges [29], and the new foundation system of the wooden shell, consisting of RC perimetral curbs and micro-piles (Figure 3). The AdESA LFRS also encompasses floor diaphragms, either obtained by exploiting the existing floors or by introducing new intrados steel trusswork and steel-string courses to transfer the floor's inertia forces to the AdESA shell. The structural shell requires three different types of connections: (1) connections among the panels; (2) connections between the shell exoskeleton and the existing building; (3) connections between the shell exoskeleton and the foundation system. The connections can be conceived to be either \"over-resistant\", i.e., designed to behave elastically throughout the seismic event, or \"dissipative\", to amass damage and to cap the seismic actions. Three examples of over-resistant and dissipative connections, specifically conceived for the AdESA system with horizontal panels, are reported in Figure 4. In the over-resistant solution, the lower panel is first stud-connected to the floor RC ring beam, and the upper panel is then connected to the lower panel by means of nailed steel strips; conversely, in the dissipative solution, an array of vertical steel plates is interposed at the connection level. Depending on the arrangement of the steel plates, dissipation can occur either in the shell exoskeleton, i.e., at the interface between the upper and lower panels, to cap the maximum actions in the shell, or between the shell and the existing building, i.e., at the interface between the shell exoskeleton and the string course fixed to the existing floor ring beam, to limit the maximum transferred shear floor action. The study of dissipative connections has led to the development of miniaturized connections, with weight and dimensions that can be handled manually by a single worker and composed of standardized elements that can be easily implemented according to specific needs. Figure 3: Structural layer of the AdESA system. In the case of CLT panels arranged vertically, it is possible to adopt additional types of connections, concentrating the dissipation at the interface between adjacent panels. The panels are designed and cut to adapt to the geometry of the building facade, considering openings, balconies, lodges, overhangs, etc. In case of great irregularities to the facade, such as extended ribbon windows or lodges, a hybrid wooden-steel shell may also be adopted.