# Seismic Isolation Devices for Protecting RC Buildings: The Frangipane School in Reggio Calabria
## 2 Seismic Isolation Devices  
As known, the dynamic response of an isolated building (both new and existing) strictly depends on the mechanical characteristics of the isolation devices in use, as well (depending on the technology in use) and on their optimal installation and placement in the building layout [1].  
For the presently reported application, sliding isolator devices, as in Figure 3a, i.e., friction pendulum type, are used for seismic retrofit of the investigated building (Figure 3b). According to the technical documentation of the producer [24], these seismic devices (PS 1400/600 type) are characterized by an equivalent radius of 2300 mm and can offer a design friction coefficient of up to 4.7%. They are designed to accommodate a lateral displacement of 250 mm in seismic conditions (and up to 300 mm). Their typical constitutive behaviour under horizontal forces can be seen in Figure 3c, as obtained from dedicated experimental certification [25], according to [26]. Figure 3d shows their typical experimental response under vertical loads [25]. The major advantage of sliding bearings, as in Figure 3, is that they support the weight of the primary structure on a bearing that rests on a sliding interface [27; 28]. As such, maximum benefits and protective contributions (in terms of the dynamic response of the retrofitted system) can be expected under seismic events.  
Figure 3: Isolation system in use for the present study: (**a**) cross-sectional schematic view and (**b**) in-situ installation in the Frangipane School in Reggio Calabria (detail), with (**c**) experimental response under horizontal and (**d**) vertical forces.  
For the present application to the Frangipane school building, the choice of seismic devices and retrofit intervention based on base isolation was mainly dictated by the primary need to avoid structural interventions on the load-bearing elements of the upper floors. Also, the specific type of devices, as in Figure 3, was selected on the base of preliminary considerations about the layout of a case-study building.  
In the last few years, the upper stories of the examined building have been, in fact, the object of several interventions and renovation activities (i.e., for the electrical system, but also for video surveillance tools, fire prevention and internet networks), as well as the object of intervention for replacement of original fixtures (doors and windows). Therefore, a possible seismic retrofit intervention based on necessary structural reinforcements for load-bearing components (such as concrete beams and pillars), as well as the possible installation of supplementary brace systems (for improving the global performance of the building to horizontal design loads), would have resulted in a major disassembly or even destruction for most of the above-renovated facilities/services and refurbishment activities.  
Finally, sliding devices, as in Figure 3, were preferred to other technological solutions because torsion motions of the primary structure are usually minimized, given that the centre of stiffness of the isolators automatically coincides with the centre of mass of the supported system. The friction pendulum bearings have strong resetting and self-limiting capabilities, low sensitivity and high stability to the seismic excitation frequency range, and excellent energy dissipation capacity [29].