Dynamic characteristics of the west wing of East Block of Parliament Hill, Ottawa, Ontario from ambient noise recordings

Abstract

To mitigate seismic risk, it is important to obtain a structure's natural frequencies and resonant amplification spectra. To this effect, ambient seismic noise data were collected at three sites of interest as well as two reference sites within the west wing of East Block on Parliament Hill in Ottawa, Canada due to the importance and historic value of these heritage buildings. The data were processed using the standard spectral ratio (SSR) and horizontal-to-vertical spectral ratio (HVSR) techniques. Processing of the ambient noise data for the South-West Tower yielded approximately the same fundamental frequency (2.0 Hz) as did the analysis of the Mw 5.0 Val-des-Bois earthquake data (1.86 Hz). Several >3 Hz spectral peaks as well as broadband amplification (3 Hz - 8 Hz) were observed at room 219 and room 314 of the west wing at the locations of previously installed three-component earthquake accelerometers. The SSR technique was found to be more reliable than the HVSR technique in identifying the dominant peaks in the spectra. This was likely due to the presence of vertical amplification at the sites which is hypothesized to be caused by coupling between the horizontal vibrational modes with that of the floor which caused it to vibrate at a comparable frequency. An ambient noise survey such as the one performed in this work is a low-cost approach for documenting the dominant dynamic properties of a structure in the linear domain.