PSI - Issue 84

Marco Civera et al. / Procedia Structural Integrity 84 (2026) 49–56

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In particular, the envisioned anomaly detection concept will resort to both data-driven and model-based thresholds, as it will be further detailed in future contributions, using measured data and a calibrated Finite Element (FE) model. Therefore, this brief document summarises and discusses the preliminary considerations made in the earliest months of the project. In particular, Section 2 outlines the bridge’s critical structural features. This operational evaluation includes the current structural system, also in light of historical inspections, maintenance, and retrofitting works, as documented in retrieved technical reports, and in the context of its surrounding geotechnical and geological aspects. All this information defines the anticipated structural criticalities and guides the design of the SHM system, as discussed in Sections 3 and 4. Finally, the Conclusions (Section 5) end this short article. 2. Operational Evaluation. 2.1. Original Structural System As sketched in Fig. 2.a, the Amedeo VIII bridge is a five-span structure with a maximum span length of 31.2 m and a total length of 138.2 m (axis-to-axis of supports; circa 153.3 m including the abutment seats at both ends, see Fig. 2.c). At these two ends, the superstructure is anchored to the ground by counterweights (light grey L-shaped area in Fig. 2.c), which have been schematised as clamped constraints in Fig. 2.a. Then, the remainder of the superstructure rests on four intermediate piers, each one 4.5 m tall and made of the same R.C. as the deck. At the second and fourth spans, the bridge features structural half-joints (the so-called ‘Gerber saddles’) and 15 m-long simply supported suspended spans. According to the original structural drawings, these Gerber saddles are also reinforced by external steel strengthening frames, even though this cannot be confirmed by direct visual inspection, as they are not visible. These half-joints represent the first and most important aspect to monitor, as they are renowned structural weak points, for several reasons (Palmisano et al., 2023). First, they transfer high levels of shear forces at a reduced bearing area, causing stress concentrations at the re-entrant corner. Second, they are vulnerable to accelerated deterioration due to exposure to water infiltration through joints. Third, due to their short, block-like geometry, they are prone to concrete crushing, which is a fragile failure mode. Finally, due to the structural scheme, their sudden local rupture would have severe consequences, with the collapse of the entire suspended span. Transversely, the bridge actually consists of two adjacent multi-cell box girder decks (‘ impalcato 1 ’ and ‘ impalcato 2 ’ in Fig. 2.b), placed side by side and connected during construction, for a total width of 20.4 m. There are no reinforcing bars passing from one box girder to another; therefore, they must be considered structurally independent from each other. However, the two decks rest on the same bridge piers, so any anomaly on the piers should be transmitted to both. Together, the two decks support a single four-lane carriageway (two lanes in each direction, for a total of 15.0 m, along with two 2.70 m-wide lateral sidewalks). The ten variable-height longitudinal beams have a constant spacing at all cross-sections as reported in Fig. 2.b. The slab thickness is constant along the bridge main axis as well; conversely, the decks’ beam web (‘ bw’ ) varies as portrayed in the bottom half of Fig. 2.b, while the beams’ height ranges from a minimum of 1.58 m at mid-span to a maximum of 2.68 m over the piers. Similarly, the counter-slab has a minimum thickness of 6 cm at mid-span and a maximum of 20 cm over the abutments and piers (see also Fig. 2.c). All these main beams are connected to each other through the slab on the extrados, the counter-slab at the intrados, and by crossbeams (joists) located at the supports and along the span as portrayed in Fig. 2.c. Overall, this cross-sectional geometry does not require any significant precaution, also considering that the bridge has load restrictions for exceptional transports and that surveys after the 2011 retrofitting did not mention specific weaknesses. Notably, the bridge lacks properly deep foundations; they consist of R.C. caissons, sunk by their own weight, without piles. The foundations are embedded into dense gravel and can be classified as rigid caisson foundations, since their slenderness ratio (i.e., the height-to-base ratio) is 3.5. Nevertheless, this design solution is potentially endangered by scouring phenomena (Aimar et al., 2024), making the pier foundations the second weak point of the current structure. In fact, among the potential natural hazards, the hydraulic risk is the most prominent one: the surrounding area is categorised as Class IIIb2b (areas potentially floodable in catastrophic events, but buildable with technical precautions) according to the Regional Law, and at high flood risk according to https://idrogeo.isprambiente.it/. Furthermore, the same area is interested by a phreatic aquifer at ~5 m depth, with possible rises of 0.5–1.0 m after intense rainfall.