PSI - Issue 78

Enrico Bernardi et al. / Procedia Structural Integrity 78 (2026) 599–606

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assumed). A superstructure was added to the existing structure, considering a mass ratio ( μ ) equal to 0.25, 0.5, and 0.75. Regarding the performance parameter, values of β =0 and β =0.5 were considered. The structural representation, as well as the optimal dimensionless parameters of the isolation system, are shown in the Figure 5.

Fig. 5. Case study structure, modal characteristics and the optimal isolation parameters.

Eight time history analyses were performed using natural seismic records selected from the strong-motion database ESD (Ambraseys et al. 2002). The main characteristics of these records are summarized in Table 1. The seismic signals were scaled to match, on average, the Type 1 elastic response spectrum defined by Eurocode 8 (EC8), assuming a peak ground acceleration (PGA) of 0.3 g.

Table 1. Details of the selected records.

ID

Earthquake

Date

Mw Epicentral distance [km]

Scale factor

Acc.1 Acc.2 Acc.3 Acc.4 Acc.5 Acc.6 Acc.7 Acc.8

Montenegro (aftershock)

1979/05/24 1980/11/23 1992/03/13 1999/09/07 1980/11/23 1978/09/16 1999/09/07 1979/04/15

6.2 20 6.9 33 6.6 13 6.0 18 6.9 33 7.3 57 6.0 20 6.9 25

5.42 3.02 0.59 3.51 3.04 1.71 0.32 0.66

Campano Lucano

Erzincan

Ano Liosia

Campano Lucano

Tabas

Ano Liosia Montenegro

The results obtained are presented in Figures 6 and 7. Figure 6 shows the inter-story drifts of the existing building model, both with and without the IIS. The findings indicate that the use of the IIS system significantly reduces the drift in the substructure. Moreover, structural control via the IIS also contributes to a more uniform drift distribution along the height of the structure, as the variation in drift between different floors is notably reduced when the isolated superstructure is introduced. In all cases, the most effective solution corresponds to the optimization with β = 0. This outcome is expected, as β = 0 is associated with the optimization strategy aimed at minimizing the displacement response of the substructure. Nevertheless, the solution with β = 0.5 also achieves a significant reduction in substructure drift. Among the two optimization strategies considered, OPT2 provides higher performances in terms of drift mitigation. The effectiveness of the IIS solution does not appear to be significantly influenced by the mass ratio μ . Figure 7 illustrates the results in terms of: maximum substructure drift, drift of the isolation system ( D IS ), and superstructure acceleration ( A IS ). The results demonstrate that the solution with β = 0 yields an optimal configuration in terms of the dimensionless displacement parameter θ L , consistent with the trends shown in Figure 6. As for the