PSI - Issue 78

Andrea Pozè Falet et al. / Procedia Structural Integrity 78 (2026) 325–332

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Table 2. Modal parameters (first bending mode), 2004 (post-retrofitting), for all bridge spans C1 C2 C3 C4 C5

± 0.18

1 [Hz] 1 [-]

4.70 7.05 ∙ 10 −2 4.13 ∙ 10 −2 3.04 ∙ 10 −2 3.66 ∙ 10 −2 3.60 ∙ 10 −2 4.30 ∙ 10 −2 ± 1.59 ∙ 10 −2 - - 4.41 4.40 4.75 4.75 4.60

MAC( , , ,∎ ) 1.0000 0.9988 0.9989 0.9945 0.9988 Table 3. Evolution of modal parameters, 2003 vs 2004, for all bridge spans C1 C2 C3 C4

Δ Δ

C5

1 [Hz] 1 [%]

0.02 0.43

-0.11 -2.43

-0.27 -5.78

0.06 1.28

-0.16 3.26

Δ 1 [-] 2.25 ∙ 10 −2 2.32 ∙ 10 −2 -1.05 ∙ 10 −2 0.04 ∙ 10 −2 -1.80 ∙ 10 −2 Δ 1 [%] 46.88 128.18 -25.67 1.10 -33.33

Finally, comparing Tables 2 and 4 offers a glance at the current state of the bridge. In short, all the natural frequencies and all the MAC values are generally lower, probably due to normal wear and tear over the years. These differences between 2004 and 2024 are reported in Table 5, again both in absolute and relative terms. Instead, the reduction in the MAC on spans C3 and C4 (although with minor entity compared to 2003 data on C2) and the pronounced asymmetries in the mode shapes in those spans compared with the 2004 measurements suggest a potentially anomalous behavior, that may be attributed to the scouring of pier P4 (however, these points are currently being addressed in ongoing studies, also considering higher modes and more extensive comparison between spans, not limited to C1).

Table 4. Modal parameters (first bending mode), 2024 (current situation), for all bridge spans C1 C2 C3 C4 C5

± 0.13

1 [Hz] 1 [-]

4.36 2.83 ∙ 10 −2 0.70 ∙ 10 −2 1.69 ∙ 10 −2 0.79 ∙ 10 −2 0.90 ∙ 10 −2 1.38 ∙ 10 −2 ± 0.90 ∙ 10 −2 - - 4.32 4.27 4.48 4.60 4.41

MAC( , , ,∎ ) 1.0000 0.9937 0.9964 0.9887 0.9970 Table 5. Evolution of modal parameters, 2004 vs 2024, for all bridge spans C1 C2 C3

Δ Δ Δ Δ

C4

C5

1 [Hz] 1 [%] 1 [-] 1 [%]

-0.34 -7.23

-0.09 -2.04

-0.13 -2.95

-0.27 -5.68

-0.15 -3.16

-4.22 ∙ 10 −2 -3.43 ∙ 10 −2 -1.35 ∙ 10 −2 -2.87 ∙ 10 −2 -2.70 ∙ 10 −2 -59.86 -83.05 -44.41 -78.42 -75.00

4. Conclusions This short paper presented a dynamic identification study of the Strambino bridge, twenty years after a central pier experienced scouring and was subsequently retrofitted. Structural Health Monitoring (SHM) techniques were used to assess the bridge’s condition, using output -only dynamic identification (Operational Modal Analysis – OMA). In particular, modal parameters were compared over time and over space (different spans). Over time, campaigns conducted in 2003 (pre-intervention), 2004 (post-intervention), and 2024 have been compared. The modal parameters - natural frequencies, damping ratios, and mode shapes – show noticeable variations before and after retrofitting, as well as in current conditions; however, without statistical thresholds, it is not yet possible to assess, for each span, if these differences may or may not be indicative of actual scouring. Over different spans, the current state (as of 2024)