PSI - Issue 78

Alessandro Fulco et al. / Procedia Structural Integrity 78 (2026) 2054–2061

2055

1. Introduction The paper concerns the seismic improvement of a strategic building located in the municipality of Perugia in Central Italy. The building, according to the Technical Standards NTC (2018), falls within use class IV as "Constructions with important strategic functions" and it is already identified in this context by the municipality of Perugia in relation to the Emergency Limit Conditions (CLE) as a strategic building for the territory. Current Italian legislation has confirmed the programme for mitigating the seismic vulnerability of public buildings, and in particular strategic buildings, through specific coordination plans aimed at defining and prioritising intervention strategies in this sense. Therefore, from today's regulatory framework it emerges the absolute necessity to proceed with the seismic retrofitting of the identified strategic buildings in order to maintain the operational functions in case of emergency events, as in Fagotti et. al (2022). The maintenance of the aforementioned operational conditions also during site works is equally fundamental. Therefore, of considerable importance is the choice of an appropriate design strategy aimed at interventions that enable such scenarios. In the present case, the seismic upgrading works currently in progress fully implement the above mentioned goals, in fact, the Owner has put in place all the technical and design activities necessary for those purposes, obtaining in 2024 the technical-administrative authorizations necessary to proceed with the sismic upgrading of the structure and with the start of the work that will be concluded in the present year. The particularity of the project concerns the adoption of a strategy to increase structural safety through the technique of base seismic isolation using sliding devices (Martelli et. al 1999). This design strategy consists of decoupling the superstructure from the substructure (integral to the ground) by reducing its response accelerations by up to 10 times compared to those to which it is subjected in fixed base (ante-operam) conditions. The intervention makes it possible to achieve the expected seismic capacity conditions, together with the cancellation of the associated damage states ('Near Zero Damage'), Mezzi et. al (2019). In fact, the reduction of the seismic action on the structure also allows the safeguarding of the physical, plant and technological contents that typically characterize a strategic building. A further decisive aspect that directed the project strategy on the adoption of base isolation was to avoid the evacuation of the occupants, and the contents functional to the operational activities carried out, during the works, as well as the minimization of interference. In fact, the intervention foresees a concentration of the activities in the basement story without any further interventions in the rest of the structure. The offices and work rooms will not be directly affected by significant limitations or interference for the entire duration of the worksite, allowing them to be fully utilized. The planned intervention is characterised by the innovative nature of the technology based on the use of seismic sliding isolators, placed at the basement level, that will guarantee not only the structural adaptation but also the operation during extreme seismic events, thus making it suitable to fulfil the functions of a strategic building. 2. Description of existing structure The structure, built at the beginning of the 1990s, consists of two-way r/c frames and a staircase-elevator r/c boxed core. In elevation, the structure has a total of 4 decks, 1 of which is the basement, reaching a total height of approximately 13.10 m from the extrados of the foundations to the extrados of the top floor characterised by a flat roof. In plan, the building has an irregular pseudo-rectangular shape with variable dimensions at each level, defining a progressive reduction in square footage; the rectangle enclosing the underground portion has dimensions of 45 x 25 m (longitudinal x transversal) while the above-ground portion is 30 x 18 (longitudinal x transversal). The building in elevation is characterised by a significant tapering of the decks, in fact on level 1 there is an external courtyard used for car parking. The carpentry of the same deck is characterised by a r/c perimeter retaining wall to define the below basement. In fact, level 0, accessible externally from a driveway or internally from the stairway/elevator compartments, is used as covered parking and storage. In addition, in the basement area, there is also an archaeological find on the south side of the building, suitably protected by glass and covered on top by a r/c slab. Overall, the walkable area is approximately 3000 m 2 , while the total volume is 7200 m 3 , while it is 4200 m 3 for the above-ground part alone. The carpentry found in the original design of the work is shown in next figures. Ultimately, the structure has four decks above ground level made of single-direction brick-concrete slabs. The structural system consists of bi directional r/c frame and an inner core made of r/c walls 30 cm thick. The shaft include a staircase defined by ramped r/c slabs 20 cm thick connected to the walls. Columns are characterised by variable dimensions with 11 section types.