PSI - Issue 78

Carmine Lupo et al. / Procedia Structural Integrity 78 (2026) 185–192

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1. Introduction The advances in Seismic Engineering have highlighted that many existing structures are no longer compliant with current standards and have undergone aging processes that are not always adequately mitigated by timely and effective maintenance interventions. In an ever-changing and evolving world, the need for a safe and efficient road network is increasingly necessary to ensure a high level of service for users. The Italian road network is characterised by a large number of aging structures and a considerable variety of assets, with individual distinctive features. Furthermore, roads and bridges were originally designed and built taking into account the environmental factors of the crossed areas and the construction standards in force at the time. These conditions highlight the urgency of developing robust strategies, methodologies, and tools for the efficient and sustainable management of road infrastructure, especially in a context where such assets are often located in regions exposed to significant natural hazards and varying levels of risk. In response to these critical challenges, underscored by the collapse of the Polcevera viaduct in 2018, two pivotal milestones were established in Italy. Firstly, the National Information Archive of Public Structures (AINOP) was established, see Ministry of Infrastructure and Transport (2018). Secondly, in 2020, the "Guidelines for Risk Classification and Management, Safety Assessment and Monitoring of Existing Bridges" (LG20) were adopted, as detailed by Ministry of Infrastructure and Transport (2020). AINOP is a centralized digital platform for the systematic collection, organization, and accessibility of data related to public infrastructure assets across the Italian territory. The LG20 model posits a structured and progressive approach to the management and monitoring of bridges in Italy. In particular, LG20 introduces a multi-level methodology that initially focuses on the classification of bridges through a multi-risk, data-driven approach, culminating in the assignment of a Class of Attention (CdA). This preliminary screening phase supports the prioritization of assets based on structural, functional, and environmental risk indicators. Subsequently, the methodology provides a framework for conducting in-depth safety assessments and, where necessary, implementing monitoring systems to track the structural health of critical infrastructures over time. The results of these analyses may then lead to maintenance, retrofit or strengthening interventions, aimed at ensuring the safety and durability of the asset, as shown by Petti et al. (2023). Furthermore, the analyses suggest, in addition to widespread maintenance deficiencies, that the adopted structural typologies are a key factor in determining the observed vulnerabilities. In this context, it is essential to adopt sustainable and efficient strategies to ensure structural safety, relying on robust methodologies to improve seismic performance and to accurately assess the effectiveness of maintenance and retrofit interventions, with particular attention to bridge piers. This study focuses on evaluating the seismic performance of simply supported bridges, a widespread typology within the Italian bridge inventory, retrofitted with various types of seismic isolation devices (friction and elastomeric devices). The seismic isolation represents a low-cost and promising solution, particularly for the retrofitting of existing structures. Among the available passive control techniques, base isolation has become one of the most extensively adopted strategies for mitigating seismic effects. In building applications, its primary function is to protect the superstructure by decoupling it from ground motion. This is commonly realized by introducing isolators between the foundation and the superstructure, allowing the structure to undergo larger displacements with limited acceleration demand, as demonstrated by Naeim and Kelly (1999) and Skinner et al. (1993). In bridge structures, seismic isolation is implemented by inserting a dedicated isolation interface between the deck and the piers. This interface allows relative displacement, effectively decoupling their seismic responses, reducing the transmission of shear forces, and bending moments to the substructures (piers). The effectiveness of this approach is widely recognized, particularly for simply supported bridges located in seismic-prone areas. When properly selected and implemented, seismic isolation systems can significantly reduce structural demands and minimize potential damage in retrofitted bridge structures, as discussed by Palazzo and Petti (1997) and DesRoches et al. (2010). This study uses a methodology to evaluate the effectiveness of the retrofit strategy based on the development of fragility functions that quantify the probability of collapse, considering the seismic vulnerability of the bridge’s main components. Specifically, the analysis employs a multiple-level approach (MLA), utilizing a suite of 100 recorded accelerograms from past real earthquakes with magnitudes ranging from 5 to 9. The seismic input includes both near fault and far-field events. Furthermore, several intensity measures (IMs) were analyzed, namely: Magnitude, Arias Intensity, Peak Ground Acceleration (PGA), and a fourth parameter referred to hereafter as Sabetta V. This last