Fast Bayesian Method for Assembling Mode Shapes

Abstract eng:
Modal identification aims at identifying the modal properties of a constructed structure using measured data, including the natural frequencies, damping ratios and mode shapes. It is among the first few steps to establish the baseline properties of the subject structure. In full-scale ambient vibration tests, many situations exist where it is required to obtain a detailed mode shape of a structure with a limited number of sensors. A common feasible strategy is to perform multiple setups with each one covering different parts of the structure while sharing some reference degrees of freedom (dofs) in common. This paper presents a fast Bayesian method for modal identification that can incorporate the FFT information in different setups consistent with probability logic. The method allows the global mode shape to be determined taking into account the quality of data in different setups. A fast iterative algorithm is developed that allows practical implementation even for a large number of dofs and setups. The method is illustrated with full-scale field testing of a pedestrian bridge where a global mode shape with a large number of measured locations is identified. Figures 1-3 show the assembled mode shapes using proposed method.

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