PSI - Issue 78

Livia Fabbretti et al. / Procedia Structural Integrity 78 (2026) 823–830

825

Fig. 1. SAP2000 model of the G. Marconi school building with installed permanent monitoring system schematic.

Some of these parameters – such as vertical stiffness, high-speed and low-speed friction coefficient, and the rate parameter – are directly provided by the manufacturer. However, these are not given as precise values but rather as reference intervals, since they are derived from empirical assessments and subject to variability among devices. Other essential parameters – such as initial horizontal stiffness K 1 and effective stiffness K eff – are not supplied by the manufacturer but originate from theoretical formulations based on the device geometry and modeling assumptions. K 1 is used to represent the elastic pre-sliding behavior and is calculated as: 1 = ∙ (1) where the factor a K has been the subject of numerous experimental evaluations reported in the literature on FPS isolators, with values ranging from 23.7 up to 600, as described in Naeim and Kelly (1999), Dicleli and Buddaram (2006), Cheng et al. (2008), and Berto et al. (2013). The post-sliding stiffness is instead defined as: 2 = (2) Finally, the effective stiffness K eff – which represents the equivalent linear stiffness – is calculated as: = +  ∙ (3) where d max indicates the effective maximum deformation of the isolator. K eff therefore depends both on the geometry and axial force as well as on the identified value of the μ fast coefficient. 2.3. Need for advanced parametric identification Since the main parameters of FPS isolators can exhibit significant variations and cannot be predicted accurately a priori, estimating their actual value is critically important. To understand the influence of these parameters on the seismic response of the structure, a parametric sensitivity analysis was conducted considering different seismic intensities, as detailed in Fabbretti et al. (2025). In this study, the high-speed friction coefficient ( μ fast ), the initial stiffness coefficient ( a K ), and the rate parameter ( rp ) were systematically varied, highlighting that μ fast and a K mainly govern the overall behavior of the isolators, while rp is less influential.