# 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  
From a structural point of view, the AdESA system, conceived for traditional RC frame structures or masonry structures, was adapted to the specific features of the case-study building, i.e., to account for the presence of full-height RC cladding panels, ribbon windows, an interior intermediate floor, etc. The resulting structural shell is composed of a seismic roof diaphragm on the top, additional hybrid wood/steel headwalls along the short sides of the building, where the ribbon windows are present, and concrete walls on the long side of the buildings, obtained by simply connecting the existing RC precast cladding panels. Despite partial re-engineering, the structural concept of AdESA as an outer shell connected from the outside to the existing structure was maintained but at the expense of the sustainability of the system, the hybrid system having higher environmental impacts than the original wooden system. According to the LCT principles, the damage induced by earthquakes to the existing building and to the AdESA system was limited by adopting quite demanding performance objectives in the design of the structural shell. The design was carried out by enforcing elastic behavior and full operativity of the building at the LSLS, and a ductile failure mechanism at CLS. The design targets were selected accordingly: a maximum inter-story drift ratio at LSLS equal to 0.5% and a maximum shear action in the shell facade, equal to 600 kN. These performances were achieved by introducing dissipative connections, which were conceived to be easily demountable and replaceable in case of activation, allowing an easy, fast, and cost-effective repair of the building after strong earthquakes. The roof diaphragm was assembled above the existing roof (Figure 12) by addressing the technology and detailing presented in [29]. The diaphragm shear panel was made with 3-centimeter thick plywood panels, connected with each other by nailed steel flanges transferring the shear flow (nails \(\phi 4\times 2/5\) cm; flange: s = 2 mm), to the existing roof by means of vertical steel studs collecting seismic loads (\(\phi 20/80\) cm) and deep anchors to prevent the diaphragm buckling, connected to the peripheral walls by means of steel studs transferring the shear flow to the seismic-resistant walls (\(\phi 22/45\) cm) and thin ties preventing the wall out-of-plane overturning (\(3\phi 10\) along the short sides, and \(1\phi 10/240\) cm along the long sides, in red in Figure 12, left). L-shaped steel longitudinal profiles were introduced as perimeter chords in order to resist the bending moment (in blue in Figure 12, left). Figure 11: **(a)** Energy performances of the building in the as-is condition, **(b)** Trnsys® numerical model. Along the short side of the building, new seismic-resistant hybrid walls were placed in close proximity to the existing facades. These walls consist of CLT panels, 10 cm thick, alternating with welded steel frames (S355) made of box profiles with a rectangular section (horizontal tubular elements: 220 \(\times\) 120 mm, s = 10 mm; vertical tubular elements: 180 \(\times\) 120 mm, s = 10 mm). Steel frames were introduced due to the presence of the ribbon windows along the whole facade; a hybrid version of the AdESA structural layer, initially conceived as composed of CLT panels only, was thus obtained. The proportioning of the elements was preliminarily carried out for the facade stiffness to comply with the performance objectives by considering the shear stiffness of the wooden panels and the bending stiffness of the steel frames (Figure 13a). The structural shell rests on a new foundation system consisting of RC curbs (80 \(\times\) 30 cm, L = 1520 cm) and micro-piles at the ends (one at each corner, \(\phi\)10 cm, L = 15 m).