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Highlights: Quaking in our foundations: would Canadian buildings
stand?
Quaking in our foundations — would
Canadian buildings stand?
June 01, 2011— Ottawa, Ontario
The world watched in horror in March this year when the biggest earthquake on record in Japan triggered a tsunami that destroyed huge areas of the country's coast, took more than 18,000 lives and caused one of the world’s worst nuclear disasters. Could better building codes have helped stave off damage?
“Probably not,” says NRC structural engineer Dr. Hossein Mostafaei. “Although the disaster began with the earthquake, most of the damage was from the tsunami. When it comes to quakes and standards for new construction, Japan probably has the most rigorous building code in the world.”
Dr. Mostafaei, an expert in earthquake-resistant building design, studied in Tokyo. He learned a great deal about seismicity (the frequency and distribution of earthquakes), how quakes affect structures, and how design can counter the effects of shaking. At NRC, he applies that knowledge to improve Canadian buildings.
“Fortunately, our National Building Code does not need to account for the same levels of seismicity as Japan,” says Dr. Mostafaei. “Its requirements are designed for Canada’s relative seismic hazard.”
The Code’s provisions for earthquake resistance in large buildings are the result of the work of a highly qualified committee of building contractors, consultants, seismologists, researchers and university professors.
Thanks to the Geological Survey and Natural Resources Canada, the Code incorporates precise long-term data on the seismicity of various regions of Canada. “Each province or region can take this local data into account in their own provincial codes,” adds Dr. Mostafaei.
Although British Columbia and Quebec are more prone to quakes than other provinces, as a whole Canada faces a low probability of serious devastation.
Map courtesy of Natural Resources Canada
Stronger requirements for lateral load resistance
A key objective of the National Building Code of Canada (NBC) is to ensure that buildings can adequately resist lateral loads from natural hazards to maintain safety. Lateral loads are the horizontal forces exerted on structures by winds and earthquakes.
Cathy Taraschuk, a structural engineer at the Canadian Codes Centre at NRC, specializes in structural design. She explains that Part 4 of the Code deals with the lateral load resistance requirements for large buildings, while Part 9 deals with the requirements for residential buildings and smaller, non-residential buildings.
“Canadian homes and other small buildings are generally light wood-frame construction,” says Taraschuk. “The damage that resulted from recent earthquakes in California and Japan shows that light wood-frame buildings must have walls constructed and connected in a way that ensures an acceptable minimum performance under earthquake loading.”
In addition to changes made to the design and construction of light wood-frame buildings since the 1960s, the requirements in Part 9 of the 2010 NBC have been strengthened with respect to both seismic and wind loads.
Most of the new Part 9 requirements apply to higher risk areas of Canada, mainly the Pacific Coast of British Columbia. They include the use of wall panels that are constructed in such a way that they can transfer lateral loads to the levels below. These wall panels form planes known as braced wall bands that are continuous horizontally and vertically throughout the building, and extend from the foundation to the roof framing.
Saving lives
For both homes and larger buildings, the main goal of the Code’s seismic design provisions is to prevent building collapse to save lives. A building must remain intact long enough for people to get out safely.
Chilean house damaged by a magnitude 8.8 earthquake that shook the country on February 27, 2010.
“The requirements for large buildings far exceed the requirements for single family homes,” says Taraschuk. “There are special provisions for buildings essential to the provision of services following a disaster, such as hospitals, power stations, schools and other large buildings.”
As many disaster stricken nations know, earthquakes last only seconds but their shockwaves can be felt for many years. Thanks to extensive, long-term research on seismicity and the high standard set by our National Building Code, new Canadian buildings will be safer than ever.
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