PSI - Issue 78

Federica Rauseo et al. / Procedia Structural Integrity 78 (2026) 473–480

476

2.3. Model B Model B is developed in SeismoStruct (Seismosoft) and adopts a fibre-based nonlinear approach, employing infrmDB beam-column elements with a displacement-based formulation. Geometric nonlinearity, including large displacements and rotations, is captured through a corotational framework, as also used in other studies like those on progressive collapse resistance (Mucedero et al., 2021). The floor slabs are modelled as rigid diaphragms to simulate in-plane stiffness. In this model, a continuous foundation beam is assumed to provide distributed support along the entire base of the structure. Soil-structure interaction is represented through three-dimensional link elements that connect the continuous foundation with the ground, whose stiffness is calibrated as a function of soil properties and foundation geometry. Concrete and steel materials follow the constitutive laws proposed by Mander et al. (1988) and Monti and Nuti (1992), respectively. A visual representation of the two 3D models is provided in Fig. 2. 3. Definition of scenarios 3.1. Modelling of reinforcement corrosion In RC structures, chlorides represent a common cause of corrosion. In the case of residential buildings, the phenomenon is generally related to the transport and deposition of salts in a marine environment (Moreno et al, 2018) . The main effect of chloride attack is localised corrosion, which results in a significant reduction in the cross-sectional area of the reinforcement that is distributed unevenly along its length. This localized damage significantly impairs the mechanical properties of the steel. The corrosion process is triggered when aggressive agents reach a sufficiently high concentration, known as critical content, at the reinforcement level. The initiation period, t i , corresponding to the depassivation of reinforcement, is calculated by applying the 2 nd Fick’s law, according to the equation reported in the fib Bulletin 76 (2015), based on the concrete cover depth and on the evolution of chloride content over time. For a given assessment time t, the propagation period can be obtained as t p = t- t i , and the corresponding pit depth P x (t) is then calculated according to the formulation reported in the CONTECVET Manual (2001), by assuming a pitting factor equal to 10 and a corrosion rate I corr = 2.75 µ A/cm 2 . The residual area of the rebars and the cross-section loss are subsequently evaluated according to the formulation proposed by Val (2007), based on the hypothesis of hemispherical pitting morphology. The reduction in rebar ductility due to localised corrosion is taken into account by reducing the ultimate steel strain as a function of the cross-section loss, by adopting the exponential law proposed by Berrocal et al. (2023). Moreover, the volume expansion associated with the formation of iron oxides causes the concrete cover to crack until the cover spalls. Cracking, in turn, results in a decay of concrete cover strength, which is evaluated here according to the model of Xu et al. (2021), based on the section loss in stirrups. 3.2. Modelling of soil settlements In order to apply a differential settlement profile, a Gaussian distribution curve was selected due to its simplicity and reliance on clearly defined parameters. Specifically, the formulation originally proposed by Peck (1969) to model transverse surface settlements induced by tunnelling was adopted here despite the current study not being explicitly focused on tunnelling. The curve is characterized by its bell-shaped form (Fig. 3), where the vertical settlement at any distance x from the tunnel is described as follows: ( )= �− 2 2 2 � (1) Thus, the settlement profile is described by a distribution that only needs the definition of the following two parameters: • max representing the maximum vertical ground settlement at the surface due to tunnel excavation. It is the highest point of subsidence in the transverse settlement profile, typically occurring directly above the tunnel’s centreline. It is usually calculated as a percentage of excavation depth Z 0 as