PSI - Issue 78

Giuseppe Santarsiero et al. / Procedia Structural Integrity 78 (2026) 560–567

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In contrast, Bridge 6 (on the right) shows severe degradation affecting internal beams, consistent with the higher IDeg values recorded for T2 and T3 in span C1. Notably, widespread spalling of the concrete cover, exposed and corroded reinforcement bars, and active water infiltration are clearly visible. These observations confirm that the lack of waterproofing and proper drainage has led to advanced deterioration of internal elements, contradicting the typical expectation of edge-beam vulnerability. The consistency between numerical degradation indices and photographic evidence reinforces the reliability of the proposed methodology in prioritising inspection and maintenance actions.

Fig. 3. Visual comparison of beams’ conditions in Bridges 4 and 6.

The Degradation Index enables the selection of specific beams requiring more urgent in-depth inspections. Furthermore, poor waterproofing emerged as a recurrent factor contributing to reinforcement corrosion and concrete cover spalling. Restoration of deck slab waterproof layers is therefore recommended as a preventive action. In doing this, one must remember that in Italian bridges constructed in the 1970s, the slab waterproofing is, in most cases, totally absent. 4.2. Prioritization of restoration interventions In order to prioritise restoration interventions, it is important to get some robust insight from the available data. Fig. 4 presents the degradation indices (IDeg) of the six bridges, calculated using two complementary approaches: by averaging the total degradation index per number of spans (IDeg_p,c) and per number of beams (IDeg_p,t). Both indicators provide insight into the overall structural condition from different perspectives. The span-based index (IDeg_p,c) tends to emphasise concentrated damage in specific spans, while the beam-based index (IDeg_p,t) reflects how degradation is distributed across all individual beams. Bridge 1 consistently shows the highest degradation index in both metrics (IDeg_p,c = 22.75; IDeg_p,t = 7.58), confirming widespread and severe deterioration. In contrast, Bridges 2 and 3 display the lowest values, indicating limited damage. Bridge 5, however, exhibits a high IDeg_p,c (12.34) but only a moderate IDeg_p,t (3.09), suggesting that significant degradation may be concentrated in specific spans. This discrepancy highlights the value of comparing the two indices to distinguish between generalised and localised deterioration. Average values (8.37 for IDeg_p,c and 2.56 for IDeg_p,t) serve as thresholds for prioritising inspections and maintenance. This dual-index approach enables a robust evaluation of structural condition. Table 2 shows the degradation index values and the ranking for prioritization purposes, based on the beam-averaged IDeg. These values are accompanied by the information about the Class of Attention (Santarsiero et al. 2021) evaluated for the six bridges according to the Italian Guidelines (MIT 2020).