PSI - Issue 84

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

1138

conventional and prestressed reinforced concrete, steel structures, and composite steel–concrete solutions. A graphical representation of the various types of structures examined is provided below

Fig. 1. Representative graphs of the investigated structural types

Based on hydraulic and landslide hazard classifications and the analysis of relevant sector maps, targeted site inspections were conducted to assess the presence of scour and/or structural distress in the vicinity of the viaducts. Among the viaducts located in landslide- and flood-prone areas (PAI–IFFI–PGRA), 36 were identified, of which 13 were actually affected by these phenomena. For these structures, a targeted analysis was conducted to identify the causes, the progression of the damage, and potential safety implications, based on historical photographic records, field evidence, as-built documentation, previous inspections, and available monitoring data. No short-term critical issues were identified; however, the implementation of appropriate monitoring measures was recommended. The professional appointed to perform special inspections, and responsible for the preparation of the structural Investigation Plan as well as for the coordination or direction of the necessary testing activities, shall be a highly qualified bridge inspector, with thorough knowledge of the structural typology of the structure and of the typical vulnerabilities associated with each structural system. Such knowledge is essential for the correct interpretation of deterioration phenomena, for recognizing those specific to a given structural system, and for identifying the areas where they are most likely to occur, including hidden or not immediately detectable structural deterioration that cannot be identified through a simple visual inspection. Indeed, not all structural deterioration mechanisms manifest themselves in an evident manner. A significant example is represented by voids within the ducts of post-tensioned prestressing tendons, which may remain completely concealed and undetectable from the outside, or may only be indirectly revealed by moisture stains following the tendon profile. Additional indicators of possible anomalies in prestressing systems include local concrete swelling along the tendon alignment, resulting from corrosion processes affecting the ducts. Similarly, localized cracking patterns occurring at precast box-girder segments, beam bearings, Gerber saddles, or pier may be difficult to detect or correctly interpret without a thorough understanding of the structural behavior of the bridge and of the associated boundary conditions. As prescribed by the Guidelines, special inspections shall be accompanied by diagnostic testing activities on the various structural elements, which must be properly located based on the observed deterioration, the information required for and preliminary to the subsequent assessment phases (Level 3 or Level 4), and the possible deterioration scenarios that are not directly observable. In a post-tensioned prestressed concrete beam, it is appropriate and essential to perform endoscopic inspections of the tendons at midspan, near the supports, and in areas exposed to water percolation. Ultrasonic testing is fundamental for assessing crack depth, particularly in critical areas, in order to determine whether cracks are through-thickness or superficial. In the presence of cracking, concrete destress/or strand detension may also be performed to estimate the residual stress state.