PSI - Issue 84

Alessandro Nettis et al. / Procedia Structural Integrity 84 (2026) 653–660

654

Keywords: Steel corrosion model, prestressed bridges, post-tensioning.

1. Introduction Steel corrosion is a major degradation process affecting reinforced concrete (RC) and prestressed concrete (PC) structures during their whole service life. Today, RC and PC bridges constitute over 80% of the existing bridge stock in Italy (Salvatore et al., 2026). The construction of such bridges in Italy predominantly dates back to the period between 1960s and 1980s(Pinto and Franchin, 2010). At this time, structural designers were barely aware of the whole set of problems these structures could have faced over the years and construction errors were more likely to occur. Nowadays, the almost full absence of maintenance during the years has led to a large portion of Italian bridge stock consisting of ageing structures. Recent surveys (D’Angelo and Salvadori, 2024; Salvatore et al., 2026) suggest that a substantial amount of Italian bridge structures are girder-type, simply supported PC bridges. These bridges are among the most affected by degradation, in particular tendon corrosion, since their structural response fully relies on the state of prestressing steel tendons. Particularly, in PC bridges with post-tensioned tendons, the effects of corrosion can lead to huge reduction in structural capacity (Nettis et al., 2024). In recent years, a series of PC bridge collapse events, i.e., Annone viaduct failure in 2016 (di Prisco et al., 2023), Fossano bridge failure in 2017 and the most famous Polcevera bridge failure in 2018 (Calvi et al., 2019), have raised the public attention on the topic, unveiling a tough situation for the stakeholders and managers in the field of transportation infrastructure. These bridges were all built adopting prestressed concrete as construction technique and suffered from sudden failure generally due to lack of maintenance and construction inaccuracies. Such degrading conditions, combined with heavier traffic load conditions compared to the ones considered in old design codes (Miluccio et al., 2021), represent a huge challenge for the management of transportation infrastructure. The management of the whole set of existing structures at a regional level is hindered by the lack of sufficient economic and human resources. Hence, fast and efficient methodologies for the structural assessment of bridge structures against multiple hazards are needed and researchers are working on possible solutions (Argyroudis et al., 2020; Zhu and Frangopol, 2013). As far as post-tensioned PC bridges are concerned, specific methodologies for probabilistic structural assessment have been recently proposed by authors. In their studies, the structural assessment at a regional scale is performed through a typological fragility assessment, in which the structure is modelled via both a simplified analytical model (Nettis et al., 2024) and a refined finite element model (Nettis, 2025). It turned out that the structural performance of PC bridges with post-tensioned tendons is highly affected by corrosion of tendons over time. Hence, at the aim of providing an effective methodology for the structural assessment of these bridges, it is of paramount importance to appropriately model the effect of tendon corrosion. This paper aims at providing an advancement in corrosion modelling of steel strands in post-tensioned PC bridges. After a brief review of the state-of-the-art on the currently available geometric and mechanical corrosion models, a new geometric model is proposed, inspired by the most recent experimental studies on naturally corroded PC members (Jeon et al., 2023; Vecchi et al., 2021). Particularly, this study focuses on localised pitting corrosion and the pit morphology is modelled through a parabolic shape depending on two parameters: 1) the maximum pit depth and 2) the parabola opening. Whereas current studies suggest the computation of the corrosion pit area following a discrete classification among three different possible semicircular shapes, i.e., having upward, downward or flat curvatures, the herein proposed geometric model allows a continuous variation of the curvature manipulating only the parabola opening. Moreover, based on the experimental findings available in literature on corrosion pitting morphology (Vecchi et al., 2021), a statistical distribution is proposed for the opening parameter, allowing the user to probabilistically model the pit geometry of the single wires and then combine their response to obtain the strand model accounting for the effect of corrosion on each single wire separately. This paper is organised as follows: a state-of-the-art on the available corrosion models starting from steel rebars until prestressing strands is presented in Section 2; the detail of the geometric model and the methodology adopted to derive the statistical distributions are explained in Section 3; the obtained statistical distributions and a comparison among the possible solutions are presented in Section 4; conclusions are drawn in Section 5, and a possible employment of the probabilistic model is eventually proposed. 2. State-of-the-art 2.1. Background Corrosion of steel is an electrochemical process promoted in concrete structures by atmospheric agents like water (i.e.,