High spatial resolution modal identification of a stadium suspension roof: Assessment of the estimates uncertainty and of modal contributions

In Operational Modal Analysis (OMA) engineers are usually confronted with the challenge of extracting as much information as possible from the data collected in ambient vibration tests in order to characterize the modal behaviour of the tested structures under environmental and operational conditions. There exist several tools for this purpose that combined can be used to estimate valuable information regarding modal behaviour of the tested structures from the output vibration responses measured in these tests. In this context, this paper describes the strategies and techniques employed, as well as the results obtained from the OMA performed to identify the modal properties of a football stadium suspension roof. The main focus of the paper is the employment of state-of-the-art identification techniques, in time and frequency domain, in order to estimate the modal parameters of the roof structure with high spatial resolution for the mode shapes of vibration together with their uncertainties bounds, as well as to assess the contribution of the identified modes to the measured responses under different environmental and operational conditions. A particular challenge of the presented example is the need to simultaneously process a large number of time series (15 datasets with 12 sensors - 180 time series). At the end of the paper, the estimates provided by the ambient vibration test are compared with the ones obtained with a permanent monitoring system operating during one year, in order to evaluate the representativeness of the results provided by a single ambient vibration test.