By Dr. Niel Van Engelen
On April 20, 2018, residents of the Windsor area may have heard a rumble or felt unusual motion.
The initial assumptions on the source of the noise and motion were somewhat amusing before word spread that a magnitude 3.6 (Mw) earthquake had occurred. Most Canadians wouldn’t list earthquakes as a notable concern in their lives; however, contrary to popular belief, large areas of Canada are at significant risk due to seismic hazards.
In fact, some of the most highly densely populated areas of Canada (e.g. the west coast and the east coast along the St. Lawrence River) can and have experienced large earthquake events. A repeat of historical earthquake events in these areas could incur more than $60 billion in damage, and that’s not even the worst-case scenario!
From a structural engineering perspective, the primary objective is to protect life safety. The traditional approach to designing a structure for earthquakes anticipates and accepts that damage will occur. It is simply not feasible to design a conventional structure to withstand significant ground motions without damage. Alternatively, the structure is designed to be ductile and the damage is utilized as an energy dissipation mechanism. The major shortcoming with this approach is that often the damage is so severe that it is impractical to repair the structure and it must be demolished and rebuilt.
This methodology resulted in Christchurch, New Zealand, a city of about 370,000 people, having to demolish more than 1,000 structures in the central business district after a series of earthquakes. Although life safety was generally protected in these structures,
the social and economic impacts of the demolition can’t be understated.
Seismic base isolation is a state- of-the-art approach to earthquake engineering that decouples a structure from strong ground motions. It requires the installation of a specialized layer of flexible devices, known as isolators, usually at the foundation of the structure. During an earthquake, the deformation is concentrated at the isolation layer, which can undergo large displacements without any damage.
This mechanism is effective at protecting the occupants and preventing damage to the structure and the contents even during large earthquakes.
Canada has thus far lagged other countries, such as Japan and the United States, in adopting this technology. Provisions for base isolation have only recently been included in the National Building Code of Canada. Base isolation remains an active area of research to develop new types of isolation devices, to improve upon existing methods, and to better understand the expected structure response. Undoubtedly, base isolation will become a common feature of Canadian cities, aiding to mitigate the significant risk that earthquakes present.
Dr. Niel Van Engelen is an assistant professor in the University of Windsor’s Civil and Environmental Engineering Department. He specializes in seismic and vibration isolation and structural control. This article is featured in the 2018 issue of Windsor Engineering (WE).