Modal identification of a pedestrian bridge by output-only analysis

Abstract

The modal parameters (natural frequencies, mode shapes and damping ratios) describe the dynamic properties of a mechanical system. The classical modal analysis, based on Frequency Response Function, require measurements of both the input force and the response. Normally, it is very difficult to measure the excitation on large structures (bridges, tall buildings, offshore platforms, etc.). However, reasonable estimates of the modal parameters can be extracted from ambient vibration or output-only response (wind, traffic, humans, etc.). The dynamic behaviour of a curved pedestrian bridge in the University of Seville (Spain) has been investigated by full-scale testing and theoretical models. Nine vibration modes have been identified in the frequency range of 0-20 Hz, by the following algorithms: Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI). Ambient modal parameters estimation have been compared with a rigorous three-dimensional finite element model, showed very good agreement.