Modal parameters (natural frequencies, mode shapes and damping ratios) describe the dynamic properties of mechanical systems. Classical modal analysis, based on Frequency Response Function, require measurement of both input force and response. Normally, it is very difficult to measure the excitation on large structures (bridges, tall buildings, offshore platforms, etc.). However, reasonable estimates of 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 Cartuja Campus of the Universidad de Sevilla (Spain) has been investigated by full-scale testing and numerical models. Nine vibration modes have been identified in the frequency range of 0-30 Hz, by the following algorithms: Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI). Modal parameters estimated from ambient response are compared with those obtained from a three-dimensional finite element model. Both sets of results show very good agreement.
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