PSI - Issue 84

Fulvio Busatta et al. / Procedia Structural Integrity 84 (2026) 797–804

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As shown in Fig. 4, eight vibration modes are bending modes of increasing complexity (denoted as B1-B8 in Table 1) and three identified modes are torsion modes (denoted as T1-T3) involving − in turn − spans 4, 2 and 3.

Table 1. List of the identified modes and selected modal features. Mode # Mode type f SSI (Hz) ζ SSI ( % ) MPC (%) 1 B1 – Bending 0.85 0.9 99.9 2 B2 – Bending 1.23 1.5 100.0 3 B3 – Bending 1.67 1.4 100.0 4 B4 – Bending 2.71 2.1 98.7 5 B5 – Bending 3.14 1.9 98.6 6 B6 – Bending 3.70 1.8 99.7 7 T1 – Torsion 3.99 1.9 98.6 8 T2 – Torsion 4.05 1.9 96.0 9 B7 – Bending 4.16 1.8 90.6 10 T3 – Torsion 4.25 1.6 92.9 11 B8 – Bending 4.41 1.6 97.3

4. Selected outcomes from continuous SHM The monitoring program of the Torrente Reggia bridge has been ongoing since late May 2024, and this section presents selected outcomes obtained during the first year of continuous monitoring (31/05/2024 – 31/05/2025). In this regard, Fig. 5 shows the modal tracking of the 11 natural frequencies of the bridge deck along with the tracking of the air temperature measured by the thermocouple installed close to pier #1 (see Fig. 2). a)

b)

Fig. 5. Time evolution of (a) the identified and tracked natural frequencies and (b) temperature from 31/05/2024 to 31/05/2025. All the eleven natural frequencies that were tracked show a seasonal variation over time, with decrease in natural frequencies occurring when the environmental temperature increased. Conversely, the natural frequencies of the bridge increased in the autumn/winter season, when an expected temperature drop was recorded. Some statistics on the modal parameters over the first year of monitoring are summarized in Table 2.