PSI - Issue 84

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

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3. Dynamic identification of the bridge deck Within the framework of vibration-based SHM, a preliminary OMA of the structural system was performed by using the SSI-COV identification technique (Peeters & De Roeck, 1999) with the twofold objective of understanding the dynamic behavior of the bridge deck and identifying the modal characteristics (i.e., natural frequencies, damping ratios and mode shapes) that will be monitored continuously. In other words, these modal estimates will constitute the reference vibration modes to be used in performing the modal tracking.

Fig. 3. Stabilization diagram of the bridge deck obtained through the SSI-COV identification technique. In this regard, a data file with 1-hour long acceleration time-histories being collected during a working day at the beginning of the SHM program was used. The raw time-series sampled at 100 Hz were subsequently pre-processed by applying i) linear detrending, ii) low-pass filtering with 10 Hz cut-off frequency, and iii) down-sampling so that the new sampling frequency is equal to 20 Hz. The SSI-COV technique implemented in the Python version of the P3P software made use of the following: a) time-lag ranging from 0 to 1.5 s (30/20); b) minimum and maximum model orders respectively equal to 22 and 122 (in steps of 2); c) minimum Modal Phase Collinearity (MPC, Pappa et al., 1993) equals 80%; d) Modal Assurance Criterion (MAC, Allemag & Brown, 1982) and frequency tolerances both equal to 3%, and e) minimum cluster size equal to 12. The eleven vibration modes of the bridge deck that were identified are shown in Figures 3-4 and the related modal parameters are summarized in Table 1.

b) Mode 2: f SSI = 1.23 Hz

a) Mode 1: f SSI = 0.85 Hz

c) Mode 3: f SSI = 1.67 Hz

e) Mode 5: f SSI = 3.14 Hz

f) Mode 6: f SSI = 3.70 Hz

d) Mode 4: f SSI = 2.71 Hz

h) Mode 8: f SSI = 4.05 Hz

g) Mode 7: f SSI = 3.99 Hz

i) Mode 9: f SSI = 4.16 Hz

j) Mode 10: f SSI = 4.21 Hz k) Mode 11: f SSI = 4.45 Hz

Fig. 4. (a-k) Identified vibration modes of the bridge deck.