PSI - Issue 78

Anna Brunetti et al. / Procedia Structural Integrity 78 (2026) 1729–1736

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1. Introduction In the field of pedestrian bridges, the vibrations induced by pedestrian loads and wind action represent an increasingly significant design challenge, particularly considering recent developments in calculation methods and construction materials (Van Nimmen et al. 2017, Drygala et al. 2019). These advances have given rise to the employment of lightweight and slender structures characterised by minimal visual impact and highly integrated into the surrounding landscape. However, these characteristics also give rise to issues relating to serviceability and operational behaviour (Ferreira et al. 2019). In fact, slender structures are particularly sensitive to dynamic actions, such as those generated by pedestrian flow, which can lead to significant vertical and lateral vibrations. While vibrations do not necessarily compromise structural safety, they can cause discomfort and a sense of insecurity for users (Nicoletti et al., 2023). This paper presents the procedure adopted for assessing the serviceability of a newly designed steel pedestrian bridge under pedestrian loads through numerical simulation. The vibration analysis was carried out according to Sétra's guidelines (SÈTRA/AFGC 2006), using steady-state analysis to evaluate the maximum acceleration experienced by users at each resonance-susceptible frequency. The study includes the design of tuned mass dampers (TMDs), aimed to mitigate vibrations caused by pedestrian loads at frequencies for which resonance could compromise the comfort level. TMDs ensures an optimal level of comfort for users, even under potentially critical dynamic conditions. 2. Description of the case study The examined case study is a newly constructed pedestrian bridge over the Cesano River in the Marche Region (Fig. 1). The bridge has 3 spans of 55, 86 and 54 m, for a total length of 200 m. The deck accommodates a 5.00 meter-wide pedestrian and cyclist path, with 3.00 m designated for cyclists and 2.00 m for pedestrians. The central span features an inclined arch aligned on one side of the deck that is continuous with the two box girders supporting the side spans, located on the same side. The deck has a hybrid cross-section, combining a partially box-shaped and partially open design: the box section has a trapezoidal shape, while on the opposite side, a tubular element runs along the length of the bridge, connected to the box section by solid-web transverse members (Fig. 1). In the central span, the deck is supported by stay cables, in the side spans, the deck is supported in an eccentric position by a tubular structure that is continuous with the arch, assisted by a secondary, smaller tubular beam on the opposite side. The suspension system comprises 19 stay cables made of I-shaped steel profiles welded directly to the deck and the arch. Both the central and side spans are supported by reinforced concrete piers, which have a rectangular cross-section with variable width. As for the support configuration, the superstructure is connected to the piers through fixed devices, while unidirectional bearings are used at the abutments allowing longitudinal thermal distortions.

Fig. 1. Aerial view of the bridge over the Cesano River (left) and side span cross-section (right).

2.1. Preliminary complete ambient vibration tests A comprehensive dynamic characterization of the bridge was performed to determine its modal properties in terms of resonant frequencies, damping ratios, and mode shapes. This initial characterization is essential to calibrate the finite element model and ensure it closely reflects the actual structural behaviour, which is crucial for conducting