PSI - Issue 78

Galileo Tamasi et al. / Procedia Structural Integrity 78 (2026) 883–890

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and Wagner, 2024). The 1980 Irpinia earthquake further drove modernization, leading to stricter classifications and the introduction of ductility and limit state design principles, enabled by the early use of advanced computational tools (Gizzi and Potenza, 2020). 3. Evolution of traffic loads on bridges Traffic loads on Italian bridges have evolved over time (see Fig.2), reflecting the increasing weight and volume of vehicles (Bencivenga et al., 2022; Buratti et al., 2019). For road bridges, early regulations began with the Ministry of War Circular 7100/1930 (Boglione, 2003), introducing 1st and 2nd category bridges, followed by the Normal Circular No. 8/1933, which added a 3rd category. Over the next decades, various circulars (1945 – 1962) reinforced this classification, while the 1970 Public Works Circular extended it to steel bridges. By the 1970s, bridge design typically accounted for uniformly distributed loads (to simulate traffic congestion) and concentrated loads from single heavy vehicles. Despite being issued in 1939, Royal Decree-Law No. 2229 remained a key reference for structural overloads. Manual calculations and early desktop or pocket calculators were still the standard tools for engineers. Railway bridge loads were governed by State Railways standards, using predefined train models (e.g., FS Type A and B) designed to generate maximum stress.

Fig. 2. Timeline of bridge traffic loads.

These schemes gradually became outdated as traffic and axle loads increased. In response, regulations were progressively updated: the 26 march 1980 Ministerial Decree reaffirmed the bridge categories and introduced general technical criteria, followed by updates in 1984, 1990, 1991, 2005, and 2008 (NTC 2008), with growing attention to performance and safety. The 2018 update of the technical standards for construction (NTC 2018) moved toward more generic classifications, while italian road bridge guidelines – recently updated with Ministerial Decree 1 July 2022, n. 204 - introduced new transitability categories based on vehicle type (Natali et al., 2023; Renzi et al., 2023). Adapting road bridges designed under 1970s standards to current norms - especially in terms of traffic and seismic performance - remains a major challenge in managing Italy’s aging infrastructure. 4. Concrete bridge design in the 1970s In 1970s Italy, bridge design, particularly for prestressed concrete, was a rigorous process driven by strong theoretical knowledge and practical experience, despite the limited computational tools available. Engineers relied heavily on manual calculations, often aided by tables, nomograms, and simplified formulas. Structural layouts favored analytically manageable schemes like simply supported or continuous beams. Designers widely used official regulations (laws, ministerial decrees, and circulars) and comprehensive engineering manuals. Among the most authoritative were Hoepli’s Manuale dell’Ingegnere "il Colombo" (Colombo, 1971) and Manuale dell'ingegnere civile “Cremonese” (Pantaleo, 1960) , and specific treatises on bridges by various authors of