PSI - Issue 78

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

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1. Introduction Contemporary structural engineering uses incredibly sophisticated computational tools that can tackle complex problems with a level of detail unimaginable just a few decades ago. These advancements stand in stark contrast to the early days of computing in Italy, where the first computers were introduced around the mid-1950s (Ausiello and Gambosi, 2021; Cignoni, 2013; De Marco et al., 1999). However, this increasing numerical complexity can sometimes obscure the fundamental principles of structural behavior and the design logic that guided the construction of many existing infrastructures (Benvenuto, 1991; Kurrer and Ramm, 2018; Wells, 2010). This paper aims to "step back" to the early 1970s, focusing on bridge seismic design practices in Italy. The goal is twofold: to reconstruct the methodological and computational context of that era and to demonstrate how a "simulated design" based on period specific tools and knowledge can be a valuable aid for understanding, evaluating, and validating modern analyses of existing structures. Ultimately, grasping the original design philosophy of a bridge is fundamental for effective and informed interventions, contributing to the preservation and enhancement of infrastructural heritage. 2. Main evolution of seismic regulations in Italy The evolution of seismic regulations in Italy has been closely tied to major earthquakes (see Fig.1), which have acted as catalysts for regulatory reform and technical advancement (Romeo and Pugliese, 2000; Slejko et al., 2022). Initial norms, such as Royal Decree No. 193/1909 following the 1908 Messina – Reggio Calabria earthquake, introduced basic construction requirements. Subsequent events, including the 1915 Avezzano and 1930 Irpinia earthquakes, led to refinements in design criteria with the Royal Decree-Law No. 682/1930, grounded in empirical rules and equivalent static force methods. A major shift occurred between 1960 and 1980, culminating in Law No. 1684/1962 after the Irpinia-Basilicata earthquake. This law expanded seismic classifications, introduced the seismic coefficient (C), and formalized equivalent static analysis based on mass-proportional lateral forces - marking the start of a more systematic and technical approach to seismic design.

Fig. 1. One century of earthquakes and changes in Italian seismic regulations.

Until the mid-1970s, Italian seismic regulations focused on global resistance and stability, with design prescriptions compatible with manual or calculator-based computations. The 1968 Belice earthquake exposed the fragility of non engineered and historic buildings, reinforcing the need for seismic classification and retrofitting (Petino et al., 2022). The Ministerial Decree of May 30, 1974, although not exclusively seismic, strengthened structural verification practices by integrating seismic forces from the 1962 law. At the time, dynamic analyses and ductility-based design were rare, constrained by limited computational capabilities. The 1976 Friuli earthquake marked a critical turning point, revealing regulatory deficiencies even in moderately classified zones and accelerating the implementation of Law No. 64/1974 and related decrees, which introduced broader zoning and initial concepts of response spectra (Geipel