PSI - Issue 78

Gabriele Fiorentino et al. / Procedia Structural Integrity 78 (2026) 245–252

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1. Introduction Bridges are critical components of road transportation networks, ensuring connectivity across natural and artificial obstacles such as rivers, valleys, and other infrastructure. Their strategic role makes them essential for economic activity and can be key in emergency response. The failure or disruption of a bridge can lead to significant socio economic consequences, underscoring the importance of its structural integrity, durability, and resilience. The tragic collapse of the Morandi Bridge in Genoa sparked a national debate on the state of conservation of Italy's bridge network. This infrastructure is managed by a variety of stakeholders, including publicly owned bodies such as ANAS (Italian Road Network Authority), local authorities, and private companies, highlighting the complexity and fragmentation of responsibilities in ensuring structural safety. The Italian Superior Council of Public Works has published the "Guidelines for the Risk Classification and Management, Safety Assessment, and Monitoring of Existing Bridges" (Ministry of Infrastructure, 2020). These Guidelines establish a standardised, multi-level procedure (ranging from data collection to visual inspection, risk classification into five attention classes), safety evaluation, and dynamic monitoring to assess and manage existing bridges across Italy. In addition, it features a multi-risk approach, including Structure-foundation, earthquake, landslide and flood. Following the publication of the guidelines, infrastructure owners initiated intensive inspection campaigns at various levels defined by the guidelines, achieving very high levels of detail in some instances. The A2 highway, also known as the Mediterranean or Salerno-Reggio Calabria highway, was realised between 1962 and 1974. Given the particular characteristics of the landscape, it features a large number of viaducts and bridges, including some of the highest viaducts in Italy and Europe (e.g. Viadotto Italia). In this work, a case study of an existing highway bridge viaduct in the Calabria region (Italy) is presented. Bridges supported by tall piers, such as the 130 m-high prototype examined here, behave as exceptionally slender cantilevers, with long natural vibration periods. While in this range, the elastic acceleration response has already decayed into its displacement-controlled branch, the corresponding displacement spectrum exhibits an almost linear increase with natural period. Consequently, bridges with tall piers can experience very high lateral drifts even under moderate spectral accelerations (Pu et al., 2018; Chen et al., 2019). Some authors (e.g., Tubaldi et al., 2014) have focused on the effect of higher-order modes on the seismic performance of slender bridge piers. After introducing the case study and the site, including the definition of seismic input in terms of natural and simulated ground motions, the numerical model of the two main typologies of the tallest piers of the cantilever bridge is presented. As a preliminary phase, the relevance of Soil-Structure Interaction (SSI) is investigated, and the results of the modal analysis are presented and discussed. 2. Case study The viaduct Stupino is located in Southern Italy, along the A2 Salerno-Reggio Calabria Highway, spanning a 150 m deep valley between Rogliano and Altilia. The viaduct was constructed between 1966 and 1968 during the highway's development, and since then, the only major intervention has been the installation of an external prestressing system between 1991 and 1994. An extensive investigation campaign carried out over the past few years has assessed the conservation status of the bridge, revealing typical ageing effects expected in a structure over 50 years old. The Reinforced Concrete (RC) viaduct is approximately 635m long and is formed by two independent carriageways (northbound and southbound), as shown in Figure 1. The bridge consists of nine spans. The three central piers are monolithic cantilever piers, each supporting two cantilever spans. Consequently, the lateral cantilever spans are 70 m long, while the two central spans have a total length of 120 m. The lateral spans are simply supported, with each pile supporting a single carriageway spanning 50 m. The spans are connected by hinges, allowing horizontal and rotational movements and fixing only vertical displacements. This is also one of the primary reasons to conduct an in-depth study on the seismic behaviour of the structure. The bridge was designed by Italian Engineer Silvano Zorzi and realised using the " peau-à-peau " (i.e., skin-to-skin) construction technique, which employed the Dywydag patent developed in Germany by Ulrich Finsterwalder in 1950. Zorzi had already applied this technique to the Genoa-Sestri Levante highway with the Nervi, Sori and Veilino viaducts. The method was based on the symmetrical advancement of prestressed concrete elements from both sides of a span without any support. Each ashlar was cast in place and immediately prestressed, allowing the cantilever arms