PSI - Issue 78

Ana Avramova et al. / Procedia Structural Integrity 78 (2026) 1633–1640

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at assessing the health condition of a structural system based on the continuous measurement of response data through arrays of appropriate sensors. The process often involves the extraction from measured data of features (Figueiredo and Brownjohn, 2022), which are representative of the health condition and the classification of those features to detect any novelty or abnormal change in the investigated system. In the last decades, the SHM strategy based on vibration monitoring and operational modal analysis (OMA, i.e. the output-only identification of modal parameters) has received increasing attention, and many dynamic monitoring systems have been installed, especially on bridges (Wong, 2004; Ni et al., 2008; Peeters et al., 2009; Magalhães et al., 2012; Cross et al., 2013; Cunha et al., 2013; Gentile and Saisi, 2015). The raising scientific and practical interest on dynamic monitoring and vibration-based SHM of bridges has many motivations, such as: (a) the non-destructive and non-invasive application in operational conditions; (b) the ageing of existing bridges combined with increasing of service loads and climate changes; (c) the increasing complexity of new bridges (where the implementation of monitoring systems is definitely convenient because it is possible to amortize the costs within the construction process); (d) the technological (hardware and software) advances, allowing relatively cheap installation of monitoring devices, fully computer-based operation, quick transmission and accurate processing of the collected data. However, most of the permanently instrumented bridges are concrete or steel infrastructures characterised by a complex structural arrangement, such as cable-stayed and suspension bridges or arch bridges (Wong, 2004; Ni et al., 2008; Peeters et al., 2009; Magalhães et al., 2012; Cross et al., 2013; Cunha et al., 2013; Gentile and Saisi, 2015), whereas there is a lack of studies of multi-span composite bridges. On the other hand, steel concrete composite bridges have become a very common solution in modern bridge engineering due to their optimal strength-to-weight ratio, quick time of erection and sustainability. The present study presents the results collected during the first year of dynamic monitoring of the Olona West bridge. Located in the province of Varese and spanning the Olona River, the bridge is composed of steel – concrete composite deck supported by reinforced concrete piers and abutments. After a concise description of the structure and the deployed monitoring system, the paper introduces the software tools employed to process the continuously acquired data within a statistical pattern recognition framework. The dynamic characteristics of the bridge are then presented and discussed, later focusing on the OMA-based monitoring strategy and the results obtained over one year of continuous observation, with particular emphasis on the influence of environmental factors on the variation of natural frequencies. In the final part of the paper, the application of two different novelty analysis methods is presented: the widely used control charts based on the Mahalanobis distance (see e.g. Worden et al., 2000), and the less commonly applied cointegration technique (Cross et al., 2011), which does not require the removal of environmental and operational effects and instead relies on defining a linear combination of non-stationary monitored features. 2. Description of the Olona West viaduct and monitoring strategy The investigated infrastructure, referred to as Olona West bridge (Figure 1a), is a steel-concrete composite bridge spanning the Olona River in the province of Varese (Lombardy region, Northern Italy). The bridge has a total length of 242 meters (Figure 2) and includes four spans of varying lengths (55 m + 66 m + 66 m + 55 m) whose layout follows a slightly curvilinear plan. (a) (b)

Figure 1. (a) View of the Olona West bridge and (b) typical cross-section of the deck (dimensions in cm).