The problem of estimating frequency response functions and extracting
modal parameter is the topic of this paper. A new method based on
the Random Decrement technique combined with Fourier transformation
and the traditional pure Fourier transformation based approach is
compared with regard to speed and quality. The basis of the new method
is the Fourier transformation of the Random Decrement functions which
can be used to estimate the frequency response functions. The investigations
are based on load and response measurements of a laboratory model
of a 3 span bridge. By applying both methods to these measurements
the estimation time of the frequency response functions can be compared.
The modal parameters estimated by the methods are compared. It is
expected that the Random Decrement technique is faster than the traditional
method based on pure Fourier Transformations. This is due to the
fact that the Random Decrement technique is based on a simple controlled
averaging of time segments of the load and response processes. Furthermore,
the Random Decrement technique is expected to produce reliable results.
The Random Decrement technique will reduce leakage, since the Fourier
transformation will be applied to the Random Decrement function,
which has a natural decay.
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