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Contribution à l'utilisation pratique de l'évaluation dynamique pour la détection d'endommagements dans les ponts

Alireza Alvandi
Abstract : The thesis presents a comprehensive approach for structural assessment of bridges based on dynamic testing. The two essential stakes are respectively the dynamic realization of tests under service loads and the detection and/or localization of damage. The first objective requires the development of appropriate modal identification techniques, while the second requires powerful, sensitive and reliable techniques which do not rely on numeric models (like finite elements models) often not available for all bridges.
The first part of this thesis is devoted to the problems of modal identification under ambient excitation, such as the realization of vibration tests, the choice of excitations and the interest to involve ambient excitations for testing. This part also details a vectorial form of the random decrement technique, which will be largely used to identify the modal parameters (frequencies, modes and damping ratios) of the structures studied within this dissertation. Its development also allows to extract some statistical results of the modal estimators.
The second part presents some of the most usually used strategies for the detection and the localization of damages and which only require the estimation of modal parameters ; this is the methods of flexibility, flexibility curvature and mode shapes curvature. A damage indicator method, based on the study of strain energy ratios between two measurement series, is also presented, detailed and generalized to the cases of three-dimensional beams and thin plates. By carrying out Monte-Carlo simulations, the sensitivy of these methods and their ability to detect and locate damages have been evaluated and analyzed by studying the probabilities of detection and false alarms.
In order to provide a practical use of dynamic testing as diagnosis method, the theoretical developments have been applied, validated and compared to experimental cases of beams and bridges.
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Alireza Alvandi. Contribution à l'utilisation pratique de l'évaluation dynamique pour la détection d'endommagements dans les ponts. Sciences de l'ingénieur [physics]. Ecole des Ponts ParisTech, 2003. Français. ⟨tel-00005729⟩

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2004