PSI - Issue 84

M. Cademartori et al. / Procedia Structural Integrity 84 (2026) 384–391

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the operative with restrictions category (6%). The results for the substructures [Fig. 8] are instead distributed as follows: 43% fall within the operative category, 26% are classified as adequate, 14% meet the 44-ton requirement, 7% require carriageway restrictions, and 10% were not verified. Regarding seismic assessments [Fig. 9], 79% resulted as failed, while 21% passed.

Fig. 7. Failure mechanism observed by static assessment

Fig. 6. Critical element observed by static assessment

Fig. 8. Static assessment results for superstructures and substructures Fig. 9. Seismic assessment results

4. Challenges and considerations from recent experiences Based on the results of this bridge portfolio, it is therefore possible to draw some considerations regarding these recent experiences. In the following, four main points requiring special attention are discussed.

4.1. Results of the bridge load rating procedure and degradation phenomena

The LLGG Guidelines define a reference time for required structural interventions, which differs fundamentally from the remaining service life concept in FIB (2006). While the reference time is prescriptive and based only on current structural conditions, remaining service life follows a performance‑based approach that considers degradation mechanisms over time. Case studies show clear differences between these two methods, as illustrated in Fig. 8 and Fig. 1 0. The performance‑based approach allows time‑dependent regression of mechanical properties and thus a more accurate estimate of residual service life. For example, Fig. 1 0 shows that despite compliance with NTC18 in 2025, the actual capacity–demand intersection occurs in 2043, well before the 2075 intervention time predicted by LLGG. Nowadays,most of the structures within the national infrastructure network have exceeded their original service life and one final noteworthy result concerns the Defect Impact Assessment (DIA), which is evaluated for each degraded element of every bridge as the ratio between the capacity in the degraded condition and the capacity in the intact one. Figure 11 shows the minimum DIA value with a minimum of 34% for some bridges within the analyzed bridge stock with the corresponding critical element.