PSI - Issue 84

Alessandro Scala et al. / Procedia Structural Integrity 84 (2026) 497–504

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1. Introduction The safety condition of bridges and viaducts represents one of the key challenges in the management of transportation infrastructure networks. These structures play a strategic role in ensuring user safety and continuity of mobility, ranging from high-capacity transport corridors, such as highways and primary road networks, to secondary and local roads that are often essential for guaranteeing accessibility to smaller or isolated settlements (Proske, 2020; Zhang et al., 2022). Disruption or collapse of such infrastructures may therefore produce consequences that extend well beyond the structural domain, affecting social, economic, and emergency response systems. In Italy, a significant portion of the existing bridge stock was constructed during the post-war reconstruction period and is currently approaching or exceeding its original design service life (Di Prisco, 2019). Aging materials, cumulative degradation, and heterogeneous maintenance practices have progressively increased the vulnerability of many structures. The collapse of the Polcevera Viaduct in Genoa in 2018 clearly highlighted these issues and emphasized the consequences of inadequate monitoring and maintenance strategies (Milillo et al., 2019). In response, the Italian Ministry of Infrastructure introduced the Guidelines for the classification and management of bridge risk (MIMS, 2022), aimed at standardizing inspection procedures and supporting network-level prioritization and safety assessment (Santarsiero et al., 2021). Alongside structural aging, an additional and increasingly relevant factor affecting bridge safety is the growing frequency and intensity of extreme events, as highlighted by Gabrieli et al. (2025) and expressed in figure 1. Over recent decades, Italy has experienced a marked increase in intense rainfall episodes and other extreme weather phenomena, with documented impacts on hydrogeological processes and infrastructure systems (Brunetti et al., 2004). Many existing bridges were designed considering return periods and environmental actions that may no longer be representative of current climatic conditions, thus exposing them to loading scenarios beyond their original design assumptions (Nasr et al., 2020).

Fig. 1. (a) “Progressive” and (b) “Paroxysmal” evolution of bridge degradation over time (from Gabrieli et al., 2025).

Extreme events (see figure 2) may interact with bridges through different mechanisms. In some cases, the action is direct, such as intense rainfall leading to flooding, overtopping, or riverbed erosion, which may cause foundation scour and loss of structural stability (Wang et al., 2017). In other cases, the interaction is indirect, as rainfall infiltration may reduce slope stability and trigger slow or rapid landslides that affect bridges through progressive deformation, debris flows, or impact mechanisms (Canuti et al., 1985). These processes may alter both the timing and severity of damage, limiting the possibility of detecting precursor signs and implementing timely mitigation measures. Several studies have addressed bridge failures from a statistical perspective, identifying dominant causes and long term trends at national and international scales (Proske, 2020; Zhang et al., 2022). More recently, attention has been devoted to the increasing association between bridge collapses and extreme meteorological events, highlighting the role of climate change in shaping emerging infrastructure vulnerabilities (Nasr et al., 2020). However, less emphasis has been placed on how extreme events influence failure mechanisms and damage severity, and on the implications of these effects for bridge management and risk mitigation strategies.