PSI - Issue 84

Alessandro De Iasio et al. / Procedia Structural Integrity 84 (2026) 952–958

954

Fig. 1. (a) “Pesco di Faggio” viaduct, (b) viaduct profile, (c) viaduct piers cross-section.

2.2. Impact model The impact simulations are carried out using dynamic Finite Element simulations using the commercial software Abaqus (Abaqus, 2024). A solid debris impact model is used, which was extensively validated by De Iasio et al. (2024), and replicates both the structure and debris to directly account for the debris-structure interaction in a variety of debris and structural properties (De Iasio et al., 2025b, 2025a). In this study, the pier is modelled independently of the rest of the structure (Fig. 2-a). The pier geometry is fully replicated. The bottom base is fixed. The top is unconstrained, given the limited restraint provided by the simply supported desk beams. A fictitious block with mass = 825688 is put at the pier top to simulate the deck presence. Regarding the inundation scenario, a water depth ℎ =2 and a Froude number = 1 , i.e. the critical of an idealised open channel, see Chow (1959) are assumed. Using the classical relation = v /√ ℎ , the fluid velocity v is equal to 4.43 m/s. Note that this inundation scenario is not specifically related to the viaduct area but is intended only to represent a realistic hydraulic condition. Here, the impact of a waterborne log debris is assumed to occur at the pier short side (Fig. 2-a, b), i.e. the side likely exposed to a flash flood occurring in the valley crossed by the viaduct (see Fig. 1-b). In particular, the impact location is defined at the midspan of such a short side, at the same height as ℎ , and with impact velocity v equal to v (Ruffini et al., 2021). Both debris and structure are assumed to be elastic to maximise the impact force (De Iasio et al., 2025a), and globally assess the structural behaviour under debris impacts (De Iasio et al., 2025b). No material damping is introduced as it does not influence the maximum structural under impulsive actions such as impacts (Clough and Penzien, 1993). Default Abaqus bulk viscosity damping is present to act on high-frequency oscillations at the element level (Abaqus, 2024). The pier material is defined using Young’s modulus = 30000 (see Section 2.1) and density = 2500 / 3 and Poisson’s ratio =0.2 as typical of reinforced concrete. Log debris properties are determined in accordance with the minimum design requirements in ASCE/SEI 7 22 (ASCE, 2022) for debris impact design of structures in flood and tsunami scenarios. These properties are mass = 450 and longitudinal stiffness = 61300 / , which corresponds to length = 9 , diameter = 0 .3 , density = 690 / 3 and Young’s modulus = 7580 . The model is meshed with C3D8 hexahedral elements to exclude artificial energy that would affect the physically based energy balance of the explicit simulation (Abaqus, 2024). The global mesh size is 15 for the pier, chosen in line with FE simulations of tall structures (Valente and Milani, 2016), and 2 for the debris, in line with validation studies by De Iasio et al. (2024).