PSI - Issue 84

Federico Scafati et al. / Procedia Structural Integrity 84 (2026) 25–32 F. Scafati et al. / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Most of Italy's road network was built several decades ago. The design requirements established by the technical standards at the time of construction were much softer than those currently in place, especially regarding seismic actions. It should be first noted that horizontal actions have always played an important role in bridge design, particularly when considering braking forces and wind forces. Therefore, at least in areas of medium and low seismicity, a well-designed bridge was able to withstand even the design seismic actions at the site (Clemente, 2020). This could not always be true in areas with more severe earthquakes. Therefore, in many cases, bridges built before the introduction of recent technical standards are quite vulnerable to earthquakes, with an unacceptable seismic safety index, as pointed out by several analyses performed (Buffarini et al. 2023; Ormando, Lucaferri et al. 2024). This raises the issue of retrofitting, or at least improving, the seismic performance of these structures, often subject to significant traffic. The challenges are numerous and conflicting. On the one hand, there is the need to ensure an adequate level of safety that complies with current technical standards (Buffarini et al. 2022). On the other hand, there is the need to contain costs and execution times, which would lead to high management costs and damage to the economy. With these assumptions, modern anti-seismic technologies, namely seismic isolation and energy dissipation, undoubtedly appear to be optimal solutions, to be preferred to conventional ones in most cases (Clemente, 2017). This paper traces the development of seismic isolation in Italian bridges alongside the evolution of seismic hazard classification. Finally, three recent bridge retrofit projects are shown, in which isolators replaced the existing bearings. 2. Evolution of seismic classification of Italian territory Most bridges and viaducts in Italy were built when the seismic classification was significantly different, or even when the area under consideration was not classified as seismic. This situation requires a complex process for assessing existing bridges and, where necessary, planning for retrofitting them, based on a deep knowledge of their static and dynamic behavior (Clemente, 2025). Fig. 1 shows some of the most significant classification maps, which provide an idea of the classification evolution. This classification essentially followed the seismic events as they occurred since the 1908 Messina and Reggio Calabria earthquake. For example, while the map issued in 1935 considered Calabria, northeastern Sicily, and zones of the central Apennines as seismic areas, the 1975 map, issued after the 1968 Belice earthquake, declared 25% of the Italian territory seismic, classified into two categories. The 1981 map, drawn up after the 1976 Friuli and 1980 Irpinia earthquakes, increased the percentage of the national area considered seismic to over 40%, also introducing a third category. Finally, the map issued in 2003 considered the entire Italian territory as seismic, although in zone 4 the local governments were free to decide whether to require seismic assessments for projects in those areas (PCM, 2003).

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Fig. 1. Italian seismic classifications of (a) 1935, (b) 1975, (c) 1981, (d) 2003.