Abstract: During a football game, the ambient vibrations at the roof of a
football stadium were recorded. A very large data set consisting of 4 hours of
data, sampled at 80 Hz, is available. By a data reduction procedure, the
complete data set could be analysed at once in a very short time. The data set
was also split in shorter segments corresponding to certain events before,
during and after the game to investigate the influence of varying operational
conditions on the dynamic properties. As the structural vibrations were caused
by unmeasurable wind and crowd excitation, Operational Modal Analysis has to be
applied to find the dynamic characteristics of the structure. The new
operational PolyMAX parameter estimation method is used and compared with
Stochastic Subspace Identification. Stochastic Subspace Identification requires
the correlations between the responses as primary data, whereas PolyMAX
operates on spectra or half spectra (i.e. the Fourier transform of the
positive time lags of the correlation functions). The main advantage of PolyMAX
is that it yields extremely clear stabilisation diagrams, making an automation
of the parameter identification process rather straightforward. This enables a
continuous monitoring of the dynamic properties of a structure.
