Localisation de défauts dans les structures de génie civil à partir de mesures dynamiques de déformations

This thesis focuses on the development of a new method for the continuousmonitoring of civil engineering structures in order to locate small damages automatically. Areview of the very wide literature on Structural Health Monitoring (SHM) points first out thatthe methods can be grouped in four categories based on their need or not of a numerical model,as well as their need or not of information of the damaged structure to be applied. This stateof the art of the SHM methods highlights the requirement to reach each levels of SHM, whichis in particular for the localization of small damages in civil engineering structures the needsfor a non-model based output-only damage sensitive feature extraction technique. The origin ofthe local sensitivity of strains to damages is also analyzed, which justifies their use for damagelocalization.A new method based on the modal filtering technique which consists in combining linearlythe sensor responses in a specific way to mimic a single degree of freedom system and whichwas previously developed for damage detection is proposed. A very large network of dynamicstrain sensors is deployed on the structure and split into several independent local sensor networks.Low computational cost and fast signal processing techniques are coupled to statisticalcontrol charts for robust and fully automated damage localization.The efficiency of the method is demonstrated using time-domain simulated data on a simplysupported beam and a three-dimensional bridge structure. The method is able to detect andlocate very small damages even in the presence of noise on the measurements and variabilityof the baseline structure if strain sensors are used. The difficulty to locate damages from accelerationsensors is also clearly illustrated. The most common classical methods for damagelocalization are applied on the simply supported beam and the results show that the modal filteringtechnique presents much better performances for an accurate localization of small damagesand is easier to automate.An improvement of the modal filters method referred to as adaptive modal filters is nextproposed in order to enhance the ability to localize small damages, as well as to follow theirevolution through modal filters updating. Based on this study, a new damage sensitive featureis proposed and is compared with other damage sensitive features to detect the damages withmodal filters to demonstrate its interest. These expectations are verified numerically with thethree-dimensional bridge structure, and the results show that the adaptation of the modal filtersincreases the sensitivity of local filters to damages.Experimental tests have been led first to check the feasibility of modal filters to detect damageswhen they are used with accelerometers. Two case studies are considered. The first workinvestigates the experimental damage detection of a small aircraft wing equipped with a networkof 15 accelerometers, one force transducer and excited with an electro-dynamic shaker. Adamage is introduced by replacing inspection panels with damaged panels. A modified versionof the modal filtering technique is applied and compared with the damage detection based principalcomponent analysis of FRFs as well as of transmissibilities. The three approaches succeedin the damage detection but we illustrate the advantage of using the modal filtering algorithm aswell as of the new damage sensitive feature. The second experimental application aims at detectingboth linear and nonlinear damage scenarios using the responses of four accelerometersinstalled on the three-storey frame structure previously developed and studied at Los AlamosNational Labs. In particular, modal filters are shown to be sensitive to both types of damages,but cannot make the distinction between linear and nonlinear damages.Finally, the new method is tested experimentally to locate damages by considering cheappiezoelectric patches (PVDF) for dynamic strain measurements. Again, two case studies are investigated.The first work investigates a small clamped-free steel plate equipped with 8 PVDFs sensors, and excited with a PZT patch. A small damage is introduced at different locations byfixing a stiffener. The modal filters are applied on three local filters in order to locate damage.Univariate control charts allow to locate automatically all the damage positions correctly.The last experimental investigation is devoted to a 3.78m long I-steel beam equipped with 20PVDFs sensors and excited with an electro-dynamic shaker. Again, a small stiffener is added tomimic the effect of a small damage and five local filters are defined to locate the damage. Thedamage is correctly located for several positions, and the interest of including measurementsunder different environmental conditions for the baseline as well as overlapping the local filtersis illustrated.The very nice results obtained with these first experimental applications of modal filtersbased on strains show the real interest of this very low computational cost method for outputonlynon-model based automated damage localization of real structures.Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Etude de la mise en forme des patches piézoélectriques pour le contrôle actif des vibrations -- Sciences de l'Ingénieur

info:eu-repo/semantics/nonPublishe

Electrical tuned vibration absorber: application of the equal-peak method to linear and non-linear RL piezoelectric shunts

info:eu-repo/semantics/publishe

Local modal filters for automated data-based damage localization using ambient vibrations

info:eu-repo/semantics/publishe

Comparison of damage localization based on modal filters using strains measurements and acceleration measurements

info:eu-repo/semantics/publishe

Multi-scale modal filters for early damage localization

info:eu-repo/semantics/publishe

Damage localization in bridges using multi-scale filters and large strain sensor networks

info:eu-repo/semantics/publishe

Robust virtual dynamic strain sensors from acceleration measurements

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