PSI - Issue 78

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

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The experience gained along the A3 motorway corridor, consistent with findings from other national-scale infrastructure evaluations, has highlighted that the major criticalities affecting roadway assets are fundamentally attributable to two principal factors: a general lack of maintenance and conceptual design deficiencies, as reported by Buttarazzi et al. (2023), Fox et al. (2023) and Santarsiero et al. (2021). With regard to maintenance, inspection and diagnostic investigations confirm that the accumulation of widespread degradation is strongly correlated with decades of deferred interventions and the absence of systematic asset management policies, particularly in the case of aging infrastructure. On the conceptual design side, criticalities originate from the use of non-optimal construction typologies and from the application of design standards that, at the time of conception and execution, did not account for current performance requirements including seismic resistance and design seismic actions. The situation observed on the A3 motorway is emblematic and, more importantly, representative of the current condition of a large portion of the Italian roadway infrastructure network. As illustrated in figure 1a, approximately 79% of the bridges were built before 1980, thus predating the adoption of modern seismic design codes. This evidence, when combined with the current state of deterioration and the widespread lack of seismic adequacy, highlights the urgent need for retrofit interventions that are effective, efficient, and sustainable. Additionally, figure 1b illustrates that the majority (64%) of the structures adopt a simply supported beam configuration. The predominance of this structural typology requires attention, as their structural simplicity often translates into greater vulnerability under seismic actions and long-term operational demands (Pelà et al. 2019 and Pinto et al. 2020). At the same time, with a calibrated design and the selection of appropriate support devices, such as high-damping rubber bearings or friction pendulum isolators, these structures can be effectively retrofitted to enhance both seismic resilience and durability (Buckle et al. 2006, Borzi et al. 2015 and Braga et al. 2021).

Fig. 1. Construction age (a) and Static Scheme (b) of the A3 highway bridges and viaducts.

3. Fragility Analysis and Retrofit Strategy 3.1. Case Study and Retrofit Strategy

The study focused on a representative example of bridge construction from the 1960s, characterized by a simply supported beam deck (figure 2). The deck consists of eight prestressed reinforced concrete longitudinal beams and a concrete slab. Transversely, secondary beams provide lateral connectivity between the main longitudinal elements. The piers are classified into two types, sharing the same cross-sectional geometry but differing in height: Long Piers, with a height of 41.00 meters, and Short Piers, approximately half as tall as the long piers. Although the selected geometric configuration is based on a single viaduct, it is capable of describing different configurations in terms of the span-to-height ratios of the various piers. The initial configuration employs a support system typical of historical bridge construction, comprising a combination of fixed and movable sliding bearings. A friction coefficient of 2% is assumed for the sliding devices in the structural analyses. To assess the seismic performance improvement, two retrofit strategies are considered, both involving the replacement of the original bearings with seismic isolation devices. The first solution utilizes elastomeric isolators (such as SI-N 550/154 - FIP INDUSTRIALE), designed to accommodate horizontal displacements of up to 300 mm. The second solution employs elastomeric devices with lead core (such as LRB-S 550/150-120 - FIP INDUSTRIALE),