PSI - Issue 84

Alessandro Scala et al. / Procedia Structural Integrity 84 (2026) 489–496

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inspection indices are computed using a different number of categories and are therefore not directly comparable. Consequently, the priority assigned to a bridge should only be compared with that of other structures belonging to the same Guidelines level. Nevertheless, a comparison between the two graphs clearly shows that the overall trend changes significantly following Level 2 activities, particularly for several bridges in the central portion of the sample. Visualizing some of these cases is especially informative, as it highlights how inspections can modify the information obtained during the inventory phase and, in some cases, completely alter the prioritization order derived solely from the available documentation. In this chapter, four of the most significant cases are presented, representing each one of the four main combinations of simply supported and hyperstatic structures with slow-moving and rapid landslides.

Fig. 4. The four structures described in the paper: (a) hyperstatic viaduct interacting with rapid landslide; (b) hyperstatic viaduct interacting with slow landslide; c) isostatic viaduct interacting with rapid landslide; (d) isostatic viaduct interacting with slow landslide.

The first structure (Fig. 4a), representative of hyperstatic bridges interacting with a rapid landslide, is a masonry arch railway viaduct located in Northern Italy. Although the indices were primarily calibrated for road infrastructures, it was still possible to convert the number of passengers into a corresponding daily average traffic class. The pre inspection index, equal to 0.649, is among the highest of all the analyzed case studies. This is due to the mapped presence of an unstable rock face, for which frequent rockfalls and collapses have been reported. Available documentation also indicated that past events had previously led to closures of the viaduct, although no mitigation measures or monitoring systems were mentioned. However, the inspection completely altered the initial expectations regarding the landslide risk for the structure, which initially appeared to be of high priority. The presence of extensive and effective protective measures (nets, rigid barriers, and large concrete structures positioned upstream of the piers) demonstrated that the current risk to the structure has already been significantly mitigated (Fig. 5a). The presence of debris beneath the arches confirms ongoing minor collapses, but the existing defense system effectively limits their impact on the bridge. As a result, the total coefficient value decreased significantly, to 0.234, indicating only moderate priority and reflecting a risk that is currently well managed. The second structure (Fig. 4b), representative of hyperstatic bridges interacting with a slow-moving landslide, is a mixed-material arch bridge located in Southern Italy. The only initially available information consisted of cartographic data and online inventories, in which the bridge did not appear to be involved in potential interactions with landslide phenomena. The only mapped movements concerned widespread superficial landslides that, although not directly affecting the bridge, indicated potentially unfavorable geological conditions. This resulted in a PI pre that was not particularly high, equal to 0.353. In this case as well, the inspection substantially altered the previous assessment, as all the typical signs of interaction between a hyperstatic structure and a slow-moving landslide, longitudinal to the bridge, were observed (signs that were not recorded in cartographic data). The visual survey revealed a very extensive and severe cracking pattern in the first unreinforced concrete span (Fig. 5b), with openings up to one centimeter at the intrados and damage at the crown propagating into the adjacent masonry. The roadway of the first span had completely