PSI - Issue 44

Ubaldo Saracco et al. / Procedia Structural Integrity 44 (2023) 721–728 Ubaldo Saracco et al./ Structural Integrity Procedia 00 (2022) 000–000

723

3

original state. The current and future requalification proposals of both the railway and the bridge under study are numerous. In this framework, the project "Ciclovie" presented by the Basilicata Region with resolution No. 128 of the 2017 February 24 th , which sees the re-functionalisation of the entire railway line in a cycle-pedestrian street, was selected as the winner project and is currently in the execution phase. The technical documentation obtained through the research process has brought few results. The only technical drawings available were based on plans and side views, that were preliminarily checked during the on-site inspections. Having the authorization to access around, but not into, the structure, the heights reported on the drawings received were verified through a manual measurement. Given the size of the structure, detailed measurements were conducted only for some elements. The result of this survey campaign led to highlight multiple discrepancies with the data obtained from the sketches. For this reason, considering that the purpose of this paper is the structural modelling and analysis of the bridge, a more careful geometrical survey of the structure was needed. In fact, because of the difficulty to perform a direct measurement campaign due to both the accessibility of the artefact and the excessive distances for measurements with a laser metre, an aerial photogrammetric survey via UAV (Unmanned Aerial Vehicle) was found as the only way to obtain a precise geometrical representation of the bridge structure. Thanks to this aero-photogrammetric process (Fig. 3a), it was possible to trace a lot of geometric information that cannot be obtained with other survey methods. At the end, with the help of the metric information derived from the photogrammetry, as well as with the direct and indirect metric survey carried out on site, a new CAD drawing was created (Fig. 3b) with all the information necessary for the next modelling and structural analysis phase.

a

b

Fig. 3. (a) Dense Cloud Image from Metashape Pro; (b) new CAD drawing obtained from photogrammetric process.

3. FEM modeling 3.1. Premise

FEM modelling was performed with the FaTa-Next software developed by the Stacec s.r.l. company. About the modelling process, like any structural parametric modeller, the software required the primitive definition of the mechanical parameters of materials, the geometric information of the structure, as well as the definition of internal constraints and external restraints. The limited knowledge reached, because of the impossibility of further diagnostic tests and measurements, leads to some uncertainties that will inevitably influence the analysis results, as shown in the works of Gino et al. (2021) and Castaldo et al. (2022), which are focused on slender beams, but can be extended to non-linear analysis of other types of elements. In the case under study, all the bridge components were modelled by truss elements and the structure was simply supported at ends. 3.2. Definition of materials The lack of information about the structure brings the attention also on the impossibility of clearly defining the mechanical features of the bridge. In particular, attention was paid to the study carried out by Di Lorenzo et al. (2021), which analysed the main mechanical aspects and the related standards on cast irons, wrought irons and steels from the Mid-19th Century to the present day. According to this study, the most common metal alloy identified for structures of that period was steel. Once this information level was reached, the standard closest to the construction time of the bridge was identified as the Ministerial Decree 06/05/1916 " Technical regulations concerning metal works involving public railways ". Finally, based on this standard code, the mechanical characteristics of the bridge can be considered as comparable to the actual S235grade steel ones, which were therefore used for the analysis phase of the structure .