“Better buildings would have saved lives.”
–Chuck DeMets, U.S. Geologist
DeMets, a tectonic geologist from the University of Wisconsin-Madison, reflects on the January 2010 earthquake in Haiti, described by the United Nations as the worst humanitarian crisis in decades, with a death toll ranging from 50,000 to 200,000. He predicted that “…a similar quake in California would have almost certainly had a much lower death toll. Better buildings would have saved lives.”
Canada has approximately 4,000 earthquakes recorded annually. Most of them are small of course (I personally lived through one of these in my first condo), and the majority are around B.C., our most prone province. Over the past 100 years, we’ve had at least nine quakes registering a magnitude of 7 or higher. Despite this sounding like a small occurrence however, it remains a topic of study for engineers and something that we can all benefit from, particularly when our city and our world become a more vertical place to live.
When we know better, we do better. And when it comes to building resilient buildings and how they respond to natural disasters, particularly earthquakes and seismic impact, this is no exception. Lessons learned over previous decades allow us to continuously improve our building codes and design practices. For example, there have been updates to the seismic hazard model (this outlines areas geographic areas and probability of earthquakes) which was created to be implemented into the 2015 National Building Code (NBC) of Canada (NBCC2015). This is a more current version and in replacement of the 4th Generation models used for NBCC 2010.
Equally reassuring is that improved engineering has mitigated the cost burden and it’s estimated that about 2-4% of a project cost is specifically allocated toward the aspect of earthquake “resistant” design. (Engineers do actually believe there’s a way to build earthquake “proof” buildings but the cost would be extremely prohibitive.) And so “resistant” is the happy medium, providing us with increased confidence that buildings will remain intact, without collapsing and will be able to preserve life in the event of a large earthquake. This is something worth holding on to. Particularly since engineers are adamant that earthquakes themselves don’t kill people; collapsing buildings do. (This applies to all structures – even homes, and there are some engineers that believe the taller a structure, the more flexible it actually is and the less energy needed to keep it stable during an earthquake.)
So let’s go back to the classroom and first start with an understanding of what exactly an earthquake is. Earthquakes take place when large pieces of rock in the earth’s crust move against one another. It most often takes place along a break in a body of rock that extends for miles (even hundreds of miles). Large amounts of energy are released when these pieces of rock move, which occurs in the format of seismic waves, which cause the ground to shake, what we refer to as an earthquake. The waves (both P &S) move the ground vertically and horizontally. It’s the latter that we are concerned with. Buildings are designed to tolerate vertical movements, whereas the horizontal impose a lot of stress.
DeMets earlier reflection on Haiti in 2010 seems to be far away from our reality. And in most cases, it was. The buildings there have been compared to “death traps.” They were brittle, with little flexibility that restricted their ability to absorb the movemement of the quake. There were insufficient building codes and lack of enforcement of them. And finally, the substrate of the buildings, which has a critical impact, was soil, not bedrock, which contributes to the crumbling of a building. These are all things that we are fortunate to have an awareness of in our country.
Engineers now design with flexible materials that are able to withstand specified levels of seismic movement from certain distances. Ian Main, a seismologist at the University of Edinburgh, UK compares modern building practices to that of the car industry. “Car bonnets are now designed to crumple, leaving the interior intact,” explains Main. Buildings also now have ways to incorporate materials and design practices that “help resist or minimize dynamic shear and twisting motions” caused by seismic activity and allow them to absorb the energy of the waves through the entire building. Shaking energy can be transferred downward to floors and walls and finally back to the ground. Connecting joints between structural parts of a building can also be reinforced to tolerate impact from earthquake forces.
So, what magnitude of earthquake is a Canadian building designed to withstand? This is a question often asked to the National Research Centre of Canada and the Institute for Research in Construction Canadian Codes Centre. According to NRC, the answer isn’t simple and contemplates three major things; (1) the earthquake’s magnitude, (2) its distance from the building, and (3) the building’s characteristics.
The NRC also provides examples for Canada’s largest cities.
Montreal, for example, where there is low likelihood of an earthquake greater than magnitude 7.5, mandates that high-rise structures are designed to withstand earthquakes with a magnitude of 7.0, at least 30 km away. Toronto mandates that highrises are designed to withstand magnitude 7.0 events no closer than 50 km. Vancouver (excluding Vancouver island which is an entity unto itself when it comes to earthquake risk) mimics our own in Toronto.
Another federal organization that continues research on earthquakes is the Canadian Seismic Research Network (CSRN). This particular group is dedicated to managing and mitigating the seismic risk to our urban infrastructure, focusing primarily on cities forming 2/3 of Canada’s urban population, specifically Metro Vancouver, Victoria, Montréal, Ottawa, Toronto and Québec City.
There are a lot of experts continuing to study, learn and implement new techniques to ensure that our highrise communities are smart AND safe. And with buildings getting taller, new systems are constantly being innovated. Check out this WIRED video explaining the “base isolation” technique engineers have applied to skyscrapers. This allows them to float on ball bearings, springs and padded cylinders so that the structures don’t sit directly on the ground and are not subjected to the shocks of an earthquake. It’s incredible!
Source Featured Image – flickr.com Martin Luff