PSI - Issue 84

Francesco Nigro et al. / Procedia Structural Integrity 84 (2026) 183–190

187

Fig. 5. Plan layout of the monitoring system

3. Dynamic identification 3.1. Reference OMA of the bridge

The extraction of the bridge dynamic parameters from ambient vibration data is performed through an automated OMA procedure. The identification core relies on the Covariance-driven Stochastic Subspace Identification (COV SSI) algorithm (Van Overschee and De Moor, 1996; Peeters and De Roeck, 1999). This method is particularly effective for large-scale infrastructures as it allows for the robust estimation of natural frequencies, damping ratios, and mode shapes by modelling the structural response as a stochastic process in the state-space domain. Figure 6 and Table 1 summarise the main features of the identified modes.

Table 1. Reference OMA of the bridge based on the accelerations acquired on April 14 th 2025 between 7:00 and 8:00 a.m.

Mode number Frequency [Hz] Damping [%] Cluster size

MPC [%]

MPD [%]

1 2 3 4 5 6 7 8 9

2.65 3.47 4.66 6.18 6.46 7.62 7.84 9.11

1.80 1.91 4.53 1.87 2.22 2.94 3.53 3.70 4.39 2.15 1.81 2.24 2.38

51 51 51 51 51 50 51 38 32 41 20 11 20

100

6

99 97 99 99 98 95 85 93 99 98 77 89

11 16 20 27 27 30 30 31 21 24 18 25

10.01 12.31 13.11 15.89 21.19

10 11 12 13