Recent Applications of Ambient Vibration Measurements in Croatia
The chapter describes recent applications of the measurements of ambient vibrations in Croatia. They include free-field measurements in Zagreb and Ston, as well as those done within buildings. Data obtained in the field at both localities are consistent with the properties of shallow geological structures known to exist there. In Zagreb, HVSR spectra indicate thick alluvial cover (over 100 m) that gradually gets thinner as one reaches the southernmost slopes of the Medvednica Mt. A similar situation, but on a smaller scale, is also encountered in Ston, where HVSR profiles reveal several tens of meters thick sedimentary cover over the bedrock which gets exposed at the Stoviš hill. Measurements in the buildings were analysed by FREDA—a suite of Matlab routines that permit several modes of data analyses. Based on tests on synthetic and real data we conclude that spectral methods are in general more robust and less dependent on parameters of the respective algorithm, than time-domain analyses. Spectral algorithms are also much better in resolving higher modes. The random decrement method is in most cases found to be inferior to spectral or band-pass procedures using original signals. Applications to real buildings proved that analyses of shaking induced by ambient vibrations in most cases leads to well constrained, reliable, and time independent estimates of frequencies and damping of the buildings' vibrational modes.
KeywordsHVSR Damping in buildings Building frequency Soil structureinteraction
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