Confidence Intervals of Modal Parameters during Progressive Damage Test Michael Do¨hler, Falk Hille, Xuan-Binh Lam, Laurent Mevel and Werner Ru¨cker Abstract In Operational Modal Analysis, the modal parameters (natural frequencies, damping ratios and mode shapes) obtained from Stochastic Subspace Identification (SSI) of a structure, are afflicted with statistical uncertainty. For evaluating the quality of the obtained results it is essential to know the respective confidence intervals of these figures. In this paper we present algorithms that automatically compute the confidence intervals of modal parameters obtained from covarianceand data-driven SSI of a structure based on vibration measurements. They are applied to the monitoring of the modal parameters of a prestressed concrete highway bridge during a progressive damage test that was accomplished within the European research project IRIS. Results of the covariance- and data-driven SSI are compared. 1 Introduction Subspace-based linear system identification methods have been proven efficient for the identification of the eigenstructure of a linear multivariable system in many applications. In this paper, the main motivation is output-only structural identification in vibration mechanics, of a structure subject to ambient unmeasured vibrations. The obtained modal parameters (natural frequencies, damping ratios and mode shapes) are afflicted with a statistical uncertainty, e.g. due to measurement noise, unstationarities in the excitation, or measurement data that may not be long enough to assume convergence of the identification method. For evaluating the quality of the identified modal parameters it is essential to know the respective confidence intervals of these Michael Do¨hler, Xuan-Binh Lam, Laurent Mevel INRIA, Centre Rennes - Bretagne Atlantique, Campus de Beaulieu, F-35042 Rennes, France, e-mail: michael.dohler@inria.fr, xuan.lam@inria.fr, laurent.mevel@inria.fr Falk Hille, Werner Ru¨cker BAM Federal Institute for Material Research and Testing, Division Buildings and Structures, D12200 Berlin, Germany, e-mail: falk.hille@bam.de, werner.ruecker@bam.de T. Proulx (ed.), Linking Models and Experiments, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series 5, DOI 10.1007/978-1-4419-9305-2_17, © The Society for Experimental Mechanics, Inc. 2011 237
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