Modal identification of a suspension footbridge using free vibration signatures

Abstract

The dynamic characteristics of a suspension footbridge are investigated through modal identification. Despite its appearance, the dynamic characteristics of the footbridge are atypical of suspension bridges. Human excitation was used to provide initial conditions of sufficient amplitude for generating free vibration signatures during testing. A conventional modal identification method based on least-square minimization of the discrepancy between the measured and model response is adopted for identifying the modal characteristics. The method has been augmented to allow multiple data sets to be incorporated in the identification of modal parameters. This capability is called for by the available data sets. The results show that the suspension footbridge behaves predominantly as a beam rather than as a typical suspension bridge, although the suspension hangers do contribute to stiffening of the bridge.