PSI - Issue 84

Lorenzo Sangiuliano et al. / Procedia Structural Integrity 84 (2026) 1326–1333

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The second step involves defining the parameters needed to generate a finite element model (FEM), such as Young's modulus, Poisson's ratio, material damping, and other characteristic physical parameters. This phase is made possible through the use of Grasshopper plug-ins—such as those developed by the softwarehouse Geometry Gym, which allows for direct integration with structural analysis software. Using these tools, it is possible to assign all relevant mechanical properties, such as those mentioned above, in a parametric manner. At the same time, the geometric aspects of the sections are defined, including shape, dimensions, and other attributes required for numerical discretization of the model. Additionally, at this stage it is possible to specify all the functional parameters required for a time-history dynamic analysis, solved using the modal method. These include, for example, the number of desired outputs, time-step size, modal damping ratio, and all settings related to the preliminary modal analysis: the choice of mode types to consider, the mass source to be used, the minimum and maximum number of modes to extract, and the convergence tolerance of the algorithm. It is also possible to define and position various types of loads - whether concentrated or distributed - and optionally include them in the active mass of the system (mass source), always through the tools provided by the plug-ins. The third step in this workflow is the automated generation of time-history functions of the moving loads, to be applied to the nodes describing the train's trajectory along the structure. The trajectory itself is discretized with a parametric step, allowing the user to precisely control the spatial resolution of the action. This process relies solely on two .csv files: one containing the axle spacings of the train, and the other the loads associated with each axle. Once the set of relevant speeds is defined, including multiple speeds, if necessary, the system automatically generates the time series of loads for each node along the trajectory and for each specified speed. The fourth step involves associating the resulting time-histories with concentrated forces applied to the nodes along the train’s path, and for each selected speed, a specific load combination is defined, ready to be used in the transient modal analysis (time-history). At this stage, the Grasshopper file is complete and ready for export to structural analysis software, in this case, SAP2000. The fifth step involves running the dynamic analysis of the previously defined model and exporting the time histories of accelerations and displacements at one or more control points. From these results, it is possible to process the data to evaluate dynamic amplifications, maximum displacements, and maximum accelerations induced on the deck, as well as perform any further post-processing on the results obtained. 3. 3. Application of the workflow to a case study To assess the reliability of the proposed workflow, a real case study was considered, for which the dynamic behaviour of the structure was already experimentally known through in-situ measurements, Chellini (2010). The selected structure is the Sesia Viaduct, whose dynamic response was previously characterised through an extensive monitoring campaign. In particular, experimental data were acquired by means of 64 accelerometers distributed along the entire span, allowing for a detailed identification of the modal properties and dynamic response of the bridge. This experimental dataset provides a solid reference for validating the numerical results obtained through the proposed automated workflow. 3.1. Description of the case study The Sesia Viaduct is an integral component of the Turin–Milan high-speed railway, a critical link in the north western segment of Italy’s high-speed rail network. Positioned to span the Sesia River, the structure was conceived to satisfy the stringent operational, structural, and durability standards required for high-speed rail service, while also minimizing long-term maintenance demands. The bridge comprises seven simply supported spans, each with a clear length of 46 m, resulting in a total length of 322 m (Figure 1).