PSI - Issue 84

Pasquale Bencivenga et al. / Procedia Structural Integrity 84 (2026) 264–271

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well as the overall attention class definition. Indeed, a bridge assigned a high defect level automatically falls into the high attention class, thereby requiring detailed safety assessments. This parameter is determined through visual inspections and a defect cataloging procedure that considers the significance of the defect for the stability of the structural element, its extent, and its severity. Examples of the application of these guidelines to bridge inventories and the assessment of structural conditions can be found in Rossi et al. (2023), Natali et al. (2023), and Ciminelli et al. (2025). Building on this, given that high defect levels automatically trigger detailed assessments, a structural defect index (I D ) ranging from 0 to 1 is defined for each bridge according to the conservation state. In this scale, equally spaced intervals were arbitrarily established as follows: 0 represents low defectiveness, 0.33 low-medium defectiveness, 0.67 medium defectiveness, and 1 high defectiveness. 2.3.1. Design Code evolution A significant focus in bridge assessment research concerns the evolution of traffic regulations over the decades. As documented by Buratti et al. (2019), early Italian design codes primarily referred to military loads, reflecting strategic transport requirements at the time. Subsequently, conventional traffic loads were introduced, and bridges were initially classified into three categories according to their importance and intended use. Later revisions simplified this framework into two categories, while current codes essentially adopt a single category for all bridges. In parallel, definitions of carriageways, lane widths, and the number of traffic lanes evolved, directly influencing the evaluation of both distributed and concentrated loads acting on bridge decks. Earlier regulations often relied on simplified load models and conservative coefficients, whereas more recent codes introduced refined traffic models capable of representing heavier and more variable modern vehicles. These differences in historical design criteria have a direct impact on the assessment of structural demand when comparing past and current codes. As further highlighted in some literature studies (Bozza et al., 2023 and Santarsiero et al., 2024), the use of historical design rules may lead to systematic under- or overestimation of bridge safety depending on the construction period and structural typology. This underscores the importance of accounting for code evolution in preliminary safety indices based on past-to-current load ratios, supporting rapid assessment and prioritization of interventions. 2.3.2. Past-to-current code ratios In a past study of the authors the evolution of Italian traffic loads to estimate safety indices for bridges based on past-to-current load ratios for both bending moments and shear forces was systematically analyzed (Bencivenga et al. 2022). In that work, continuous beams were considered, whereas in the present study the focus is on simply-supported decks. The analyses were carried out considering decks with different geometries, by varying the carriageway width (w) as a function of span length (l) and accounting for both first- and second-category bridges. Figure 1 presents the results of the evaluations performed only for first-category bridges, with carriageway widths equal to 6 m and 8 m with reference to positive bending moments and shear forces. Specifically, the 6 m and 8 m widths correspond, respectively, to two lanes of 3 m each and to two lanes of 3 m each with lateral banks of 1 m. The calculations were conducted according to the hypotheses of the previous study: in particular, sidewalks were disregarded, and dynamic amplification factors due to traffic loads were evaluated for each code, with the 1980 code specifically assuming an estimated value of g/q = 1 . A critical analysis of the results indicates that, for bridges designed according to the earliest regulations, specifically those issued by the Ministry of Public Works (1933, 1945) and characterized by short-span girders, the differences are especially pronounced. In these cases, the ratio M ED /M ED2018 reaches values as low as approximately 0.2. The ratio increases with span length and shows an upward trend for more recent codes. (from 1980 onwards), it assumes values almost systematically greater than 0.8. It can also be observed that, for case studies involving bridges with a span of 40 m, the current code provides maximum internal force values comparable to those obtained using previous regulations. Conversely, the 2005 code exhibits an opposite trend, which can be attributed to the dynamic amplification factors applied to traffic loads, not included in the current code adopted by the Ministry of Infrastructure (2005) and inversely proportional to girder span in earlier regulations. 2.3. Simplified Level 3 assessment