Open Collections

Kakoty, Preetish

University of British Columbia

Southwestern Canada is exposed to the 1000-kilometer-long Cascadia Subduction Zone (CSZ) off Vancouver Island which can produce large magnitude earthquakes. The last known CSZ earthquake occurred in 1700, leaving a gap in the understanding of the expected shaking intensity associated with such events. Metro Vancouver's tall buildings, primarily comprised of reinforced concrete shear wall (RCSW) structures, are vulnerable to these earthquakes because the region lies above the Georgia sedimentary basin, which can amplify ground motion shaking, particularly in the medium-to-long period range and is not accounted for in current building codes. Tall buildings constructed prior to the 1980s are of special concern because they predate modern seismic codes and are clustered in densely populated areas, raising concerns about the risks to life, property, and recovery from large earthquakes. This dissertation addresses these gaps by quantifying ground motion amplification from the Georgia sedimentary basin during CSZ earthquakes and assessing seismic performance of older tall RCSW buildings. Physics-based simulations for 30 M9 CSZ earthquakes, considering basin effects, are used to quantify site-specific basin amplification factors. A framework is proposed to integrate these factors into uniform hazard spectra (UHS) calculations to account for basin amplification effects. The results indicate strong correlation between spectral acceleration basin amplification and basin depth, with the average amplification factor at the deepest basin site is 2.24 for a 2-second period, resulting in 58% increase in UHS at the same period. For older tall RCSW buildings, collapse risk is assessed via nonlinear response history analysis of 3D models for 25 archetypes which are informed from a detailed inventory of such buildings. These estimates use hazard estimates from Canada's national seismic hazard model, that does not consider basin effects, and a "hybrid" model accounting for basin amplification. The 50-year collapse probability ranges from 6% to 40%, which increases by 33% on average with the "hybrid" model. The dissertation also includes seismic performance assessment under a M9 CSZ scenario to estimate economic losses and recovery times. The mean loss ratio for 25 archetype buildings ranges from 54% to 82%, exceeding the ~40% threshold for likely demolition, suggesting elevated levels of risk.

Text

2024-01-15

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87278

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/