PSI - Issue 84

Federico Scafati et al. / Procedia Structural Integrity 84 (2026) 25–32 F. Scafati et al. / Structural Integrity Procedia 00 (2026) 000–000

27 3

Currently, the hazard map ignores municipal boundaries and assigns hazard parameters to each point in the national territory based on varying return periods. Fig. 2 compares the Italian highway network with the current seismic hazard map for a probability of exceedance P 50 =10% in 50 years and rigid soil (type A) (Arduin et al., 2025).

(a)

(b)

Fig. 2. (a) Italian highway network with location of the three case studies analyzed in this paper; (b) present Italian seismic hazard map ( P 50 =10%, soil type A). 3. Seismic isolation and energy dissipation in bridges It is well known that a seismic isolation system consists of an isolation interface composed of a set of isolators and dissipation devices. These are placed between the substructure, which is the portion of the structure that remains anchored to the ground, and the superstructure, which is the portion of the structure that will be seismically isolated from the ground. Superstructure and substructure are completely separated by the isolation interface, resulting in a dynamic decoupling between them. Thanks to the isolation system, the superstructure is subjected to limited seismic actions, with acceleration significantly reduced. Consequently, the actions that the superstructure transmits to the substructure are also significantly reduced. Therefore, the substructure benefits as well (Clemente 2024). Several cases testify to the good performance of structures protected by new anti-seismic technologies (Clemente and Martelli, 2019). While the first effect is considered predominant in buildings, just the opposite occurs in bridges. In fact, in bridges, the superstructure consists of the deck, which is not very vulnerable to horizontal seismic actions, while the substructure includes the piers, abutments and their foundations. Isolation devices are usually inserted in place of the common support devices between the vertical structures, i.e., the piers and abutments, and the deck. These, in general, are not infinitely rigid with respect to the superstructure, contrary to what normally happens in buildings. It should be noted that seismic isolation is also particularly suitable for the retrofit of existing bridges, where the replacement of existing bearings with seismic isolators may often be sufficient for seismic retrofit. Furthermore, the superstructure and the substructure remain in a substantially elastic range for the design earthquake at the ultimate limit state (ULS). A higher reliability is even required for the isolation devices due to their critical role. In Fig. 3, the number of bridges with seismic isolation in Italy is reported. With reference to existing bridges, after a timid start between the second half of the 1970s and the first half of the 1980s, a significant increase in the number of seismic-isolated bridges was recorded from in the mid-1980s onward. This was followed by a period of gradual but slow increase, primarily due to the aforementioned reasons related to the lack of a standard. Then a certain increase occurred after the 2002 Molise earthquake. Finally, after the 2009 L'Aquila earthquake, the number of applications increased significantly. Nowadays, there are more than 2000 applications of seismic isolation in bridges in Italy. The number of applications to existing bridges is quite low compared with those to new structures, but a significant number of applications have been made in recent years (Clemente 2023, Scafati 2025). Further articles by the authors are available for details on the use of seismic isolation in bridges (Scafati et al. 2025; Ormando, Clemente et al. 2024), as well as on suitable procedures for the optimum design (Clemente and Buffarini 2010, Tripepi & Clemente 2021, Tripepi et al. 2026) and on the pitfalls that could affect the design of the different typologies (Clemente et al. 2019, Salvatori et al. 2022, Scafati et al. 2022, Ormando et al. 2021). However, the