Damage assessment of pre-stressed structures: A SVD-based approach to deal with time-varying loading

International audienceVibration-based methods are well-established and effective tools to assess the health state of civil, mechanical and aerospace engineering structures. However, their reliability is still affected by the variability of the features commonly used for damage detection. Environmental effects and changes in operational conditions are the main sources of variability in the structural response. As a consequence, the modal identification used to extract damage sensitive features has to face constricting requirements in terms of signals stationarity and performance accuracy. Moreover, with reference to the damage assessment, large variations of monitored features mask subtle effects due to damage, which remain undetected. This study is conceived to address both these issues by focusing, in particular, on the non-stationarity of the loading conditions of tensioned structures, such as cables and pre-stressed beams. The capability of spectral methods to deal with the modal identification of non-stationary systems is enhanced by a curve-fitting procedure based on nonlinear least squares optimization. Wavelet analysis is applied for comparison and validation of the FFT-based technique. Identified natural frequencies are then used for the damage detection, exploiting the capacity of singular values decomposition to discriminate between damage-related events and the intrinsic non-stationary nature of the structural response. A reduced-order realization of the features set is performed to amplify changes not belonging to measurement variability but deriving from exogenous events, such as damage. The proposed methodology is validated by experimental analyses carried out on beams subjected to time-varying loading conditions in order to simulate the health monitoring of quasi and non-stationary systems

Numerical modelling of large reinforced concrete specimens based on experimental tests from benchmark Concrack

Most infrastructures are reinforced concrete (RC) structures. And these structures have to be kept operational. For that the stackholders have to watch and observe the noticeable signs of degradation resulting from interactions between the environment and their constitutive materials. Of course, these interactions can reveal cracks which are the major worry with respect to durability and sustainability. If no maintenance or repair actions occur this durability could decrease until the serviceability becomes affected and in some cases, until the structural safety is concerned. In this framework, the French national research programme CEOS.fr (Behaviour and assessment of special construction works concerning cracking and shrinkage) has been elaborated. Its aim is to show the behaviour evolution of special concrete structures particularly their cracking states (opening and space of cracks) and develop tools allowing the structural behaviour prediction (forecast). Associated with the project CEOS.fr, an international benchmark named Concrack (Control of cracking in RC structures) dealt with the modelling of the experimental behaviour of large specimens. In that context, the authors are focused on the modelling of one tested mock-up. It is a large reinforced concrete beam named RL1 subjected to a free shrinkage test followed to a bending test. The authors are concentrated on the mechanical part. In order to model the mechanical test, a 2D plane stress model for the bending beam is performed. In this case, both concrete models are used, Mazars one [Mazars, 1984] and Ricrag [Richard et al., 2010]. The steel model is a classical hardening elastoplastic law. The Ricrag model is a law based on the thermodynamics of irreversible processes coupling elasticity, isotropic damage and internal sliding. Thus, this model could show its capacities to predict the behaviour of the structure according to the experimental results. In this study, the authors show the effect of the boundary conditions on the numerical results and his importance to get a good accordance with the experimental results. Crack openings and spaces are obtained by post processing and compared with the experimental results and the global numerical results are also compared to the experimental ones. At last, the set of the results is encouraging

Multi-domain feature selection aimed at the damage detection of historical bridges

The aim of this study is the analysis and comparison of several sets of features selected from different domains for the detection of damage induced by scour on historical bridge