Changes in SSRA Approach to be Consistent with the 6th Generation Seismic Hazard Model of Canada

Changes in Seismic Site Response Analysis Approach to be Consistent With the 6th Generation Seismic Hazard Model of Canada
In NBC 2015, amplification factors, F(T), were provided which varied based on seismic site class and the site-specific probabilistic PGA for a Site Class C reference ground condition (PGAref) at the specified hazard level. In the 6th Generation Seismic Hazard Model of Canada (SHMC-6) adopted for NBC 2020, multiple ground motion models (GMMs) are used to calculate hazard values at ground surface which include site amplification effects calculated internally using site terms specific to each GMM. Linear amplification effects are calculated based on Vs30. Non-linear amplification effects are calculated using site terms that vary as a function of the median prediction of ground motion intensity associated with each event scenario considered in the hazard model. The amplified ground motion values for each event scenario are then aggregated to generate the probabilistic hazard values for a particular site location and Vs30. This presentation will discuss the fundamental differences in the way that amplification is treated in NBC 2015 and SHMC-6. The results of a study that was carried out to implement SSRA-based amplification functions within SHMC-6 will be presented. The probabilistic UHRS generated using the rigorous method will be compared to SSRA-based UHRS generated using the NBC 2015- compatible SSRA methodology as well as a modified procedure for carrying out SSRA in a manner that is consistent with the way that non-linear amplification is treated in SHMC-6.
Chris Weech, M.A.Sc., P.Eng. - Thurber Engineering
Mr. Weech is a Senior Geotechnical Engineer in Thurber’s Victoria office, with 23 years of experience. He has particular expertise in soft soils engineering, deep foundations, and in seismic design practice. He is a member of the technical review board for the seismic retrofit of schools under the BC Seismic Mitigation Program, which is currently working on developing seismic site response analysis procedures that are compatible with the new seismic hazard model adopted by the 2020 National Building Code of Canada. He is also a member of the Task Group on Seismicity and Site Amplification for the 2025 National Building Code of Canada.
Lecture presented in Burnaby, BC, Canada on November 16, 2022. Video recorded and published with permission from Chris Weech.