PSI - Issue 78

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

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Table 1. Target values of the isolator parameters. Parameter Value μ fast μ slow rp a K 0.06 0.039 (0.65 · μ fast ) 0.03 51

3.2. Generation of reference simulated data Using this simplified model and the parameter values specified above, the dataset to be used as a reference for the optimization procedure was generated: two text files containing the time histories of the six quantities representing the 6DOF of the system. The accelerograms used to excite the 6DOF model to activate the isolation were sought among the recordings of the 1996-97 Central Italy seismic sequence, the most intense recorded in the last thirty years in the area. The search focused on recordings from stations close to Foligno and in sites with the same soil category (B) as the site where the school building is located, to reproduce realistic scenarios of isolator activation. Accordingly, the three accelerometric components (North-South, East- West, and vertical) of the recording “IT.NCM.D.IT -1997 0091” from the “Colfiorito Casermette” station were chosen. The signal (Fig. 3) was downloaded from the ITACA database (ITalian ACcelerometric Archive) and presents (Table 2) PGA values significantly higher than those of more recent events (with PGA always below 20 cm/s²), thus ensuring the triggering of the nonlinear behavior of the devices. Since the structural system is almost entirely linear-elastic and the nonlinearity is confined solely to the seismic isolators, the structure is particularly suitable for the application of Fast Nonlinear Analysis (FNA), which, in this case, enables a reduction in computational time by over 98% compared to traditional direct integration methods. This makes it possible to efficiently perform thousands of simulations within iterative parametric optimization procedures.

Fig. 3. Accelerograms recorded in Colfiorito: East-West, North-South, and vertical directions.

Table 2. Seismic events recorded in Colfiorito selected for performance evaluation. ID ITACA Date M W

RE [km]

PGA [cm/s

2 ]

IT.NCM.D.IT-1997-0091

1997-10-06

5.4

14.6

168.982

Table 3. Input/output comparison of the reference model and the model used for optimization. Model Input Output Reference model

Ground accelerogram, isolator parameters ( μ fast , rp , a K ) Ground accelerogram, accelerations of points 2 and 3 and isolator deformation (x and y directions)

Accelerations of points 2 and 3 and isolator deformation (x and y directions) Isolator parameters ( μ fast , rp , a K )

Optimization model