Problem and its Significance.

Today, the issue of mitigating the seismic vulnerability of public buildings and in particular strategic buildings is of fundamental importance. In this sense, current regulations require the achievement of seismic retrofitting conditions for buildings and the achievement of performances that maintain the operational functions of the buildings in case of extreme events. It is also equally fundamental to maintain operational conditions during construction works. Therefore, the choice of an appropriate design strategy based on interventions that allow such scenarios is of considerable importance.

 Approach.

For these purposes, the adoption of the base seismic isolation strategy using sliding or elastomeric devices is effective. This design strategy consists in decoupling the superstructure from the substructure (integrated with the ground) reducing its response accelerations up to 10 times compared to those to which it is subjected in the ante-operam conditions (fixed base). It is possible to achieve the expected seismic retrofitting conditions, together with the removal of the associated damage states ("Near Zero Damage"). The effect of reducing the seismic action on the structure also allows the protection of the physical, plant and technological contents that typically characterize a strategic building. A further determining aspect that characterizes this intervention strategy is to avoid the evacuation of the occupants and the contents functional to the operational activities carried out, during the construction site and execution phases of the works. In fact, the intervention is typically characterized by a concentration of the construction site activities in the semi-basement floor and/or at the base without further interventions in the rest of the structure. The offices and workrooms are not directly affected by limitations or interferences, thus allowing their full use.

 Results/Applications.

The paper illustrates the seismic retrofitting of a strategic building located in Perugia based on the strategy of base isolation. The project is aimed at obtaining the full seismic retrofitting performances of the building together with the removal of potential damage to non-structural elements and contents. Furthermore, the execution of the works allowed the full use of the building and its functionality.