PSI - Issue 62

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Mattia Zizi et al. / Procedia Structural Integrity 62 (2024) 430–437 M. Zizi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Existing masonry arch bridges constitute a non-negligible portion of the Italian infrastructural asset. This holds significantly true in specific regional contexts, such as the Caserta Province (Campania, Italy). According to a recent study of the authors, indeed, this structural typology represents more than 25% of the bridge stock handled by the Province, which amounts to about 700 bridges (Zizi et al., 2023). Since they were mainly conceived util the first decades of the last century and had rarely experienced structural interventions, their state of conservation, as well as structural safety, may result often inadequate. At the basis of a forward-looking handling policy of modernization of the entire network system, their preservation and conservation should be, thus, prominent. The structural assessment under traffic and seismic loads of an existing masonry arch bridge may represent a difficult challenge, because of: (i) the absence of original blueprints, (ii) uncertainties related to adopted modelling strategy, (iii) difficulties in determining the mechanical and dynamic behaviors of materials and overall structure, respectively. The absence of original blueprints, which is a recurring situation for existing structures realized before the half of the last century, may complicate the knowledge process at the base of the assessment. Accurate surveys of the internal and external geometries are thus necessary for obtaining a reliable geometrical model of the structures under investigation (Armesto et al., 2010; Riveiro et al., 2011). As for modelling strategies, several studies exist in the current literature, in which the problem of structural assessment of existing masonry arch bridge is addressed with different approaches. Structural analyses based on the limit analysis concepts can provide a conservative yet reliable estimation of the actual capacity of existing masonry bridges. Some literature examples of such an approach can be found, among other, in (Gilbert et al., 2020; Papa et al., 2021). On the other hand, accurate numerical models based on the Finite Element or Discrete Element methods, represent powerful tools for assessing existing bridges (Borlenghi et al., 2022; Pepi et al., 2021; Silva et al., 2022; Zhang et al., 2018). In these cases, material parameters should be chosen carefully, since they can have a notable effect on the analysis results (Zizi et al., 2024). Based on this, it is evident that the knowledge process plays a fundamental role in the overall assessment procedure and should be differentiated based on the objectives to be pursued. In this study, the case study of a five-span masonry arch bridge is presented, focusing on the preliminary phases of a wider activity aimed at assessing the capacity of the structure to withstand external actions (i.e. traffic and seismic loads). A survey of the external geometry was conducted, and a geometrical model obtained. Then, a dynamical characterization of the bridge was performed in order to detect the main vibrational frequencies and modal shapes. Based on this investigation, a preliminary numerical model was assembled in Abaqus software (Dassault Systèmes Simulia Corp., 2023). 2. The case study 2.1. General information The structure under investigation is the Bridge Ferdinando II, a five-span masonry arch bridge (Fig. 1). The bridge guarantees the access to the municipality Mignano Monte Lungo (province of Caserta, Italy) on the provincial road SP 14 from the statal road named Casilina. Bridge Ferdinando II overpasses, in the central span, a modest hydraulic obstacle having a torrential character, namely Rio Rava. The construction of the bridge dates back to 1853, at the behest of Ferdinando II of Bourbon. During World War II, the bridge was destroyed by the retreating German troops. No additional historical information was acquired and thus it can be admitted that the current bridge was realized during the post-war period, probably before 1950.

2.2. The structural system

The bridge San Ferdinando II counts five arched spans with 11.70 m length. The circular arches present a thickness of 1 m and are supported by rectangular piers having 3.30 m × 6.30 m rectangular cross-section at the mid-height and a total height of about 15 m.