PSI - Issue 84

Francesco Mariani et al. / Procedia Structural Integrity 84 (2026) 773–780

774

Keywords: structural health monitoring; benchmark bridge; full-scale tests; prestressed reinforced concrete bridge; modal identification; environmental effects.

1. Introduction Prestressed reinforced concrete (PSC) bridges represent a large portion of the existing bridge infrastructure worldwide (ASCE, 2021; Salvatore et al., 2026). Despite their widespread use, the structural performance of PSC bridges strongly depends on the integrity of the prestressing system and the stiffness of the main load-bearing components. Recent statistics indicate that a significant number of bridges are currently classified as structurally deficient, and major failures, such as the collapse of the Genoa Bridge in 2018, have further highlighted the urgency of reliable assessment and monitoring strategies (Paolini et al., 2026). Current engineering practice mainly relies on periodic visual inspections, which are unable to provide continuous information on structural condition and often fail to detect early-stage or hidden damage. In this context, continuous structural health monitoring (SHM) offers a valuable tool for improving the reliability and timeliness of condition assessment, especially for PSC structures, where prestress losses and degradation mechanisms are governed by complex and interacting phenomena, including corrosion, grouting defects, anchorage issues, and time-dependent effects (Sconocchia et al., 2024). Among SHM approaches, vibration-based methods and Operational Modal Analysis (OMA) are widely used due to their capability to perform output-only identification under ambient excitation (Brincker and Ventura, 2015; Worden et al., 2000; Cancelli et al., 2020). However, modal-based indicators alone may be insufficient for reliable damage localization, which motivates the adoption of hybrid monitoring strategies combining global dynamic features with local measurements. Numerous experimental studies were performed on prestressed concrete structures to investigate damage-induced variations in response and modal parameters (Limongelli et al., 2016; Gandelli et al., 2024; Giri et al., 2024). However, most previous tests have been conducted under laboratory conditions, often on reduced-scale specimens or simplified structural components and typically focus on a limited number of damage scenarios. Moreover, many studies rely on short-term testing campaigns and do not address the challenges associated with long-term monitoring, environmental variability, and operational changes, which can mask or even dominate the effects of damage in real structures (García Macías and Ubertini, 2020; Peeters and De Roeck, 2001; Yan et al., 2005). In addition, several works mainly exploit global dynamic indicators, whose sensitivity may be insufficient for early-stage or localized damage, while the use of dense and heterogeneous sensor networks remains relatively limited in the literature. The influence of changing boundary conditions and mass distribution, which frequently occur in real bridges due to maintenance or retrofitting interventions, is also rarely investigated in a systematic way. These limitations highlight the need for full-scale, long term experimental studies on real structures, specifically designed to generate high-quality reference datasets and to assess the robustness of SHM methodologies under realistic operational and environmental conditions. This paper presents the first results of the identification phase of a continuous structural health monitoring system applied to a full-scale bridge structure. The results refer to the undamaged condition and focus on the analysis of the identified modal properties, with particular emphasis on the influence of variations in boundary conditions on the dynamic response of the structure. 2. The case study bridge The case study structure is a full-scale prestressed reinforced concrete bridge (Figure 1). This structure features a single span extending 20 meters, simply supported at both ends. It is made up of three longitudinal I-shaped girders, each measuring 80 cm in height. These girders are connected by four rectangular cross beams that contribute to lateral stability and increase the overall torsional stiffness of the bridge deck. The deck is completed by a 20 cm thick reinforced concrete slab.