PSI - Issue 84

L. Fieno et al. / Procedia Structural Integrity 84 (2026) 1136–1143

1139

4. Selected Case Studies In support of the considerations presented in this paragraph, four significant case studies are reported, aimed at highlighting the importance of the bridge inspector’s attention to detail and of the correct interpretation of

deterioration indicators, even when they are not immediately apparent. 4.1. Case Study 1 – Grillage Deck with Post-Tensioned Prestressed Beams

The deck, consisting of spans composed of four post-tensioned prestressed beams, had previously undergone a rehabilitation intervention and, at a preliminary assessment, did not exhibit significant deterioration phenomena. However, a more detailed inspection allowed the identification of minor cracking, localized at the intrados of the beams near midspan, which, in the absence of a proper understanding of the mechanisms potentially responsible for their origin, could be easily underestimated or not subjected to further investigation. Light hammer percussion applied to the cracked area revealed the presence of voids and, consequently, local concrete swelling; the subsequent and straightforward localized removal of the concrete cover showed that the underlying prestressing tendons were extensively oxidized and corroded over a wide area.

Fig. 2. Partial removal of the concrete cover (left) and near-complete removal of the concrete cover (right)

This case demonstrates how deterioration that appears minor and not readily detectable may in fact conceal significant structural deficiencies, potentially compromising structural safety if left unaddressed. 4.2. Case Study 2 – Continuous Post-Tensioned Prestressed Box-Girder Deck The viaduct consists of a frame structure with five-span post-tensioned prestressed concrete decks. The deck is monolithically connected to the four intermediate piers. At the midspan section of the spans, a closure joint is present, constructed after completion of the cantilever segments. During the investigations carried out as part of the special inspection, aimed at further investigating certain deterioration phenomena that were not immediately interpretable and had been identified in the closure joint areas following the analysis of photographic documentation produced during the routine inspection, endoscopic inspections and localized concrete removal for visual inspection were carried out in order to assess the condition of the prestressing tendons. The investigations revealed that the closure joint had not been constructed in accordance with good practice, characterized by widespread voids of significant size. Furthermore, in this area, the prestressing ducts were found to be absent or discontinuous, with exposed and non-grouted tendons directly subjected to environmental exposure. This condition, likely present since the construction of the structure, did not produce immediate or critical effects on structural safety, owing to the effective drainage of rainwater from the roadway surface, which for a long period prevented water percolation along the box-girder web and the initiation of corrosion processes.