PSI - Issue 62

Ettore De La Grennelais et al. / Procedia Structural Integrity 62 (2024) 763–772 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Level of knowledge of the structure The level of knowledge of the structure represents a crucial aspect in the risk assessment of an existing bridge. In the case of a historical bridge like the one under examination, this assumes an even greater significance if possible. The Guidelines , in paragraph 6.2.3, regarding the knowledge of the structure, refer to paragraph 8.5.4 of the NTC2018 Technical Standards for Constructions (Ministero delle infrastrutture e dei trasporti, 2018) and point C8.5.4 of the implementing circular. NTC2018 prescribe defining a specific level of knowledge for any existing structure undergoing a safety evaluation or improvement interventions. The safety assessment and design of interventions on such structures are indeed affected by a different (not necessarily greater) degree of uncertainty compared to new construction projects. The actual existence of the structure allows for determining the actual mechanical characteristics of materials and various structural components, which may vary significantly within the same structure and cannot be imposed as design data to be achieved during construction, as is the case for a new construction. Specifically, for existing bridges, knowledge of the structure (geometry and construction details) and the materials it comprises, as well as the level of damage (crack patterns and settlements), is crucial. This is why "confidence factors" have been introduced, closely related to the level of knowledge obtained in investigative surveys. These factors serve to reduce the average strength values of materials in the existing structure to derive values to be adopted in the project. The knowledge-building process involves various and closely interconnected activities to be carried out with successive levels of detail to optimize both quantitatively and in terms of costs and time, the direct interaction with the structure. These activities include: 1. Historical-critical analysis; 2. Survey; 3. Geological characterization of the site; 4. Material properties. These aspects are analysed with a number of general considerations in the following with reference to the case at hand. 3. Historical-critical analysis The bridge, initially constructed in wood in 1876, underwent various phases of reconstruction and expansion over the years. After its destruction by a flood in 1882, it was reconstructed between 1884 and 1886 using an iron structure and masonry piers. In 1917, the bridge was once again destroyed during the Battle of Caporetto, necessitating reconstruction in the period 1920-1922. During the Second World War, it sustained bombing damage in 1944, leading to further reconstruction between 1946 and 1950.

Fig. 2. Bersaglieri Bridge – Historical Archive Images.