ºìÐÓÊÓƵ

Topic

Characterizing soil and structural dynamic behaviour using ambient vibration techniques for earthquake hazard assessment

School of Earth and Ocean Sciences

Date & location

• Friday, December 6, 2024
• 10:00 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. John Cassidy, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. Stan Dosso, School of Earth and Ocean Sciences, University of Victoria (Co-Supervisor)
• Dr. Tuna Onur, Department of Civil Engineering, University of Victoria (Outside Member)
• Dr. Carlos Ventura, Department of Civil Engineering, University of British Columbia (Outside Member)

External Examiner

• Dr. Carlos Herrera, Senior Seismologist, Onur Seeman Consulting, Inc.

Chair of Oral Examination

• Dr. Viviene Temple, School of Exercise Science, Physical and Health Education, UVic

Abstract

This thesis considers two problems in earthquake hazard assessment involving the dynamic (shaking) behaviour of a tall hybrid-wood building, and a preliminary assessment of site (soil) effects in shaking amplification in southwest Yukon. Ambient vibration (AV) methods, which utilize microtremor noise measurements, are employed to identify vibrational modes for both applications by quantifying the behaviour of the building and soils. This research is useful for estimating earthquake hazards, particularly building response and ground-shaking amplification, and may be applied to mitigate earthquake-induced hazards.

One of the key objectives of this research is to study the dynamic characteristics of tall hybrid-wood buildings, a growing class of structures, by identifying their vibrational mode shapes and frequencies. Specifically, the AV methodology is used to estimate the dynamic characteristics of the tallest hybrid-wood building in Canada, the 18-storey Brock Commons building at the University of British Columbia in Vancouver, BC, Canada. Horizontal translational, torsional, and rocking modes are identified, ranging in frequency from 0.94-9.08 Hz. Results reveal the fundamental period (1.06 s) is lower than the period predicted by numerical models (2.0 s), suggesting the building is stiffer than is estimated numerically. The identification of rocking modes similar to the vibrational modes of the soil suggest that soil-structure interaction contributes to these modes. As one of the first in situ modal analyses of a tall hybrid-wood building, these results contribute to improving understanding of dynamic behaviour of tall hybrid-wood buildings generally. These results may also aid in more accurately modelling and predicting the behaviour of tall hybrid-wood buildings under seismic loading.

Regarding soil studies, first estimations of local site effects derived from AV methods in the Haines Junction region (Yukon) are also presented in this thesis. Fundamental frequencies (f₀) are mapped for 23 sites where local amplification hazards are largely unknown to observe the distribution of soil depth and/or stiffness. AV measurements record microtremor seismic noise that is used to calculate the horizontal-to-vertical spectral ratio (HVSR) and identify fundamental and higher-order frequencies at sites, which represent subsurface impedance contrasts. The results presented in this report indicate that f₀ is generally low at many sites, indicating a thick layer of soft sediment overlies bedrock. Results suggest a spatial trend of fundamental frequency varying laterally, with higher f₀ values identified north of Haines Junction and lower f₀ values in south-central Haines Junction. These observations are attributed to the basin of the Dezadeash river. Higher-order frequency peaks (> 20 Hz) are identified many sites, which may represent a discontinuous near-surface permafrost layer, the presence of which is confirmed at one site.