PSI - Issue 78

Ana Avramova et al. / Procedia Structural Integrity 78 (2026) 1633–1640

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observation supports the conclusion that no significant structural anomalies have occurred in the investigated infrastructure over the 1-year-long monitoring period. (a) (b)

Figure 6. Control charts based on: (a) Mahalanobis distance and (b) cointegration residual.

Similar results have been obtained through the cointegration residual: Figure 6b shows the time evolution of the cointegration residual computed from the identified natural frequencies of the bridge, spanning one year from May 2024 to May 2025. The coefficients of the cointegration residual (Eq. 2) are estimated by applying the Johansen procedure during a reference period of 9 months. As suggested in the literature, Upper (UCL) and Lower Control Limit (LCL) in Figure 6b is defined as  3 times the standard deviation (estimated in the reference period). As expected, Figure 6b highlights that the residual remains stationary with minimal presence of outliers, once again indicating that no significant anomalies occurred during the monitoring period investigated. 5. Conclusions The paper illustrates the OMA-based strategy adopted for the SHM of a multi-span steel-concrete composite bridge, namely the Olona West viaduct, located along the Autostrada Pedemontana Lombarda in Northern Italy steel-concrete composite overpass. Preliminary investigations and the results collected in the first year of monitoring allowed the following main conclusions: 1. Within the frequency range 0–7 Hz, 14 vibration modes were successfully identified during continuous monitoring. 2. The monitoring results suggest a strong temporal consistency in the identified dynamic characteristics for the bridge, with natural frequencies exhibiting limited variability and mode shapes demonstrating remarkable time invariance, as highlighted by MAC values always very close to unity. 3. The air temperature turned out to be a dominant driver of the daily and seasonal fluctuation of the natural frequencies of all modes, with the frequency of torsion modes generally exhibiting a higher correlation with temperature fluctuations than the frequency of bending modes. 4. The analysis of OMA results and control charts based on both Mahalanobis distance and cointegration residual indicate the absence of any significant structural anomalies in the Olona West viaduct throughout the one-year monitoring period. The combined results provided by the analysis of modal parameters evolution and control charts based on both Mahalanobis distance and cointegration residual consistently indicate the absence of any significant structural anomalies in the Olona West viaduct throughout the one-year monitoring period.