PSI - Issue 64

Claude Rospars et al. / Procedia Structural Integrity 64 (2024) 716–723 Rospars & al. / Structural Integrity Procedia 00 (2019) 000–000

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using accelerometric measurements, has been studied by numerous authors on different structures such as buildings in Pnevmatikos & al. (2017), walls in Ientile & al. (2018) and in Carpine & al. (2021), bridges in Wahab & al. (1999), Maeck & al. (2001) and in Bovsunovsky & al. (2020) and other applications inVacca & al. (2018). The most common approaches to this problem are the study of the correlation between damage and the natural frequencies, mode shapes or damping ratios of the structure, and the detection of cracks from modal curvatures. However, without an experimental reference solution, the identification of local defects or nonlinearities is challenging. This paper deals with SHM using advanced modal analysis, where the Continuous Wavelet Transform (CWT) is used to process accelerometric responses. CWT analysis is a sensitive tool that requires fine tuning but provides accurate modal results. Among the different types of structures monitored, the special case of train-crossing bridges is challenging and interesting. Unlike, for example, wind excitation, water flow or traffic loads, trains produce excitation profiles that are highly localised in both the time and frequency domains, resulting in unusual responses. Due to this non-stationary behaviour, the use of the CWT is a natural fit for the modal analysis of these structures. In this respect, the main objective of this paper is to derive a "better" knowledge of the mechanical behaviour of the bridge from the CWT processing of measured accelerometric data.

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Fig. 1. Illustration of the Sens railway bridge: (a) first picture; (b) second picture.

For example, the Z24 bridge benchmark, a set of dynamic measurements from a road bridge subjected to different damage scenarios in Cremona (2004), has been continuously studied since its publication and has highlighted the complexity posed by the influence of environmental factors on the modal parameters in Abdel Wahab & al. (1999), Maeck & al. (2001), Maeck & al. (2003) and Bovsunovsky & al (2020). In this paper we use the processing of accelerometric responses of single span railway bridges measured during and immediately after a train crossing. This procedure is applied to data from high-speed trains (Z24 benchmark), more precisely French TGV trains of about 200 m length, crossing a short single railway bridge of 17.5 m length. In order to correctly interpret the behaviour of the bridge under the passing train, an analytical modelling of the system is carried out. 2. Modeling of the bridge-train systen In order to correctly interpret the behaviour of the bridge under the passing train, an analytical modelling of the system is performed. A good understanding of the expected signal shape is crucial for its analysis, as it is very different from the usual white noise excitation hypothesis often used for output-only dynamic identification. 2.1. Modeling of the bridge under the passing train There are several ways to model a train passing over a bridge, with varying degrees of complexity and accuracy. The simplest is to completely ignore the effects of the train's inertia and consider only its weight. This is a good approximation in the case of a sufficiently light vehicle, which will have a very limited effect on the modal parameters of the bridge, and provides a fairly simple solution and a good understanding of the problem. This model will be used