PSI - Issue 84

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

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can lead to the presence of full or partial void in certain sections of the ducts, rendering modelling of the initiation period extremely uncertain. Focusing on the propagation period, in recent years some studies have been proposed to model the effect of corrosion on steel strands with a twofold contribution, 1) with a modification of the prestressing steel mechanical characteristics and 2) with a steel wire area reduction. For example, new modified steel constitutive laws have been recently proposed by Yu et al. in 2022 (Yu et al., 2022). Particularly, in their experimental study on artificially corroded PC beams, they found a reduction in yielding and ultimate strain and strength of the strands, and a slight reduction also in the steel elastic modulus. Accordingly, they proposed analytical equations to model the modified stress-strain response of corroded strands. As for geometric modelling, the equations proposed by Val and Melchers (Val and Melchers, 1997) have been adopted so far in literature for the computation of pitting corrosion, extending their use to the wires of prestressing strands. Recently, Jeon et al. (Jeon et al., 2019) in their experimental study on naturally corroded prestressing strands, proposed a discrete classification of the pit morphologies detected on the corroded strands, in order to quantitatively evaluate the sectional loss of the strand. They classified pits into three types, depicted in Figure 1, and provide analytical formulas to compute the remaining steel wire area in each of the three configurations. In the proposed geometric model, pit Type I and pit Type II are obtained assigning a circular shape to the pit, whereas the pit Type III is obtained through a flat shape.

Figure 1. Corrosion pit morphologies (Jeon et al., 2019). Parameters of the analytic formulas are the pit depth , the wire radius and the three angles 1 , 2 , and 3 . Such geometric model has been considered also in following experimental studies (Franceschini et al., 2022; Vecchi et al., 2021). Particularly, Franceschini et al. (Franceschini et al., 2022) proposed new constitutive laws for corroded strands under chloride attack. Their experimental study considered naturally corroded 10-years-old PC beams subjected to marine environment. They performed an accurate detection of the pit morphologies by means of a 3D laser scanner and proof such a pit classification is useful to define different modifications of the steel constitutive law according to each pit configuration. Indeed, they showed that the analytical laws that best fit experimental data describing the variation of strength and strain of corroded wires vary upon each different pit type. As a result, regarding geometric modelling of the corrosion effects on prestressing strands (or wires), a useful pit classification in three different types is currently available in literature, based on a circular shape of corrosion pits and a single parameter, i.e., the maximum pit depth . This geometric model presents a good balance between simplicity and effectiveness in applications. However, such geometric modelling strategy allows the existence of only a discrete number of three possible values of area loss for a given pit depth. This paper proposes a new geometric modelling strategy based on a parabolic shape describing corrosion pits, aiming at filling this gap. The new strategy would benefit from the presence of a second parameter, representing the opening of the parabolic model, which allows to add more information to the geometric modelling of pits. The model keeps the maximum pit depth parameter, analytically representing the parabola vertex, and combine it with the information coming from the parabola opening, theoretically allowing an infinite number of possible pit shape for a given pit depth. In practice, the possible values of the parabola curvature must be limited in order for the model to retain physical meaning. The model is calibrated on the available database of experimental data provided by Vecchi et al. (Vecchi et al., 2021), and the obtained results maintain physical plausibility, as illustrated in Section 4.