PSI - Issue 78

Gabriele Fiorentino et al. / Procedia Structural Integrity 78 (2026) 245–252

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Table 1. Natural vibration periods of Piers 4-6 and 5 with and without SSI Fixed Including SSI T long (s) T transv (s) T long (s) T transv (s) Pier 4-6 1.093 1.072 1.095 1.073 Pier 5 2.116 1.710 2.118 1.711

Fig. 3. First (longitudinal) and second (transversal) vibration mode of Pier 4-6 (left) and Pier 5 (Right).

4. Seismic Hazard and definition of seismic input The seismotectonic setting of the Stupino Bridge area, situated within the Savuto Valley in northern Calabria, is significantly influenced by the interaction between major regional fault systems and local geological complexities. This region belongs to the broader Calabrian Arc, a geodynamically active orogenic belt characterised by complex interactions between the African and Eurasian plates, affected by both compressional and extensional tectonic regimes. According to the Database of Individual Seismogenic Sources (DISS v3.3.1), two key seismogenic sources dominate the tectonic framework around the site: a) Savuto Valley fault system (DISS-ID: ITCS111): A crustal fault source capable of generating moderate to strong earthquakes. It runs along the Savuto Valley and exerts significant structural control on local topography and river incision. b) Calabrian Arc thrust system (DISS-ID: ITSD001): A deep seismogenic source associated with the subduction and overthrusting processes that characterise the entire Calabrian Arc. It represents a major tectonic boundary where the Ionian lithosphere subducts beneath the Tyrrhenian margin. These fault systems underline the high seismic potential of the region. Historical seismicity confirms this hazard, with two major events recorded close to the site: the 1870 Cosentino earthquake (Mw 6.24), located only 8.7 km from the site, and the 1638 Calabria Centrale earthquake (Mw 7.09), with a rupture distance of 11.4 km. The latter was chosen as scenario event. The Seismic Code response spectrum was defined, which for this bridge type has a return period of 1898 years. Then, spectrum-compatible ground motions (Figure 4) were defined using two different approaches: (i) the selection of natural ground motions from the European Strong Motion Database (ESM, Luzi et al., 2020); (ii) the simulation of non-stationary stochastic ground motions with the software tool SIGMA (Fiorentino et al., 2025). The use of simulated