A reliable modal analysis is fundamental in vibration-measurements-based monitoring of large civil structures, such as the grandstands of the Meazza stadium in Milan. In this paper different techniques to extract the modal parameters out of data gathered under normal operational conditions have been compared: these methods work both in time and frequency domain,. A large amount of data has been collected since summer '03 during different sort of events: concerts, football matches and windy days; in all events a lot of different measurement points have been acquired and this allowed to apply all the identification techniques with different kinds of excitation. The comparison also takes into account the capability to correctly identify the modal parameters while reducing the number of transducers put on the structure. This will allow for a reduction of the number of transducers being part of the permanent monitoring system that is going to equip the structure in a close future.
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