The Strambino bridge, 20 years later: preliminary assessment of scour effects on a retrofitted bridge

For river-crossing bridges and viaducts, scour detection plays an increasingly critical role, especially in the context of ageing bridges and intensifying climate-related events. In this context, this study presents the initial findings of a comprehensive investigation into the Strambino Bridge, a five-span, prestressed concrete road bridge spanning the Dora Baltea River near Turin, Italy. In 2003, one of its central piers experienced significant scouring, prompting a structural consolidation that led to its complete retrofitting. Dynamic identification campaigns were conducted pre- and post-consolidation. These campaigns and their outcomes remain a notable reference for full-scale, real-world applications of vibration-based inspection for anomaly detection and Structural Health Monitoring (SHM), carried out before such techniques became widely adopted. The present work revisits these historic datasets and supplements them with new measurements performed in 2024 during a similar three-day-long campaign of output-only field tests. In particular, by applying an Automated Operational Modal Analysis (AOMA) algorithm to all recordings, the modal parameters (natural frequencies, damping ratios, and mode shapes) have been identified and compared across time (2003, 2004, and 2024) and spans (C1 to C5) for all the simply supported decks. The analysis reveals the capacity of anomaly-sensitive indices to reliably identify scour-induced effects. Furthermore, the novel 2024 data are here preliminarily interpreted according to such indices to assess the possible recurrence of scour. In conclusion, this study highlights the long-term value of dynamic (vibration-based) monitoring for the early detection of scour and structural degradation in road bridges.