Structural Identification of a Nonproportionally Damped System and Its Application to a Full-Scale Suspension Bridge

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Ambient vibration measurement is an important tool to evaluate the integrity of in-service structures. The writers apply a new structural identification method to ambient vibration data taken from a full-scale suspension bridge. The method consists of two steps: identification of vibration modes and inverse analysis of structural properties from the identified modes. For modal identification, the method treats the structure as a multi-input–multioutput system, distinguishing noise from true modes and employing ambient vibration measurement. For the identification of structural properties, assumptions on proportionality of damping, previous estimation of structural damping/stiffness, and numerical iteration are not required. Application to the Hakucho Bridge in Hokkaido, Japan, verifies that the method can precisely determine the characteristics of not only the lower modes, but also the higher modes, and can effectively detect changes in the structural properties.