Earthquake seen as wake-up call on seismic standards

Posted July 7, 2010, 8:51am EDT

Source: Daily Commercial News, June 28, 2010

The recent earthquake that shook central Ontario and part of Quebec is a wake-up call for engineers and authorities to pay more attention to seismic standards in this part of the country, experts say.

“They take it more seriously in the West and around Ottawa because of the Ottawa Valley, but in southern Ontario and near Toronto there’s still some foot dragging,” says Arsalan Mojaher, adjunct professor at the University of Toronto’s department of geology and environmental science.

“But this new seismic event is a reminder to put it back on the agenda.”

The Ontario Building Code was amended in 1974 to make seismic resistance integral to building design and construction and the sections are periodically upgraded, Mohajer said.

While post-1974 buildings are generally adequate, he said, those built before the code changes should be scrutinized, especially public institutions and nuclear facilities.

He says fault lines run across Ontario and Quebec and there’s a serious earthquake risk zone along the St. Lawrence stretching from Quebec City to Montreal and down to Cornwall.

Another fault line runs from Niagara to Pickering, through Toronto and he points to the Pickering nuclear facility as a structure that needs to be re-evaluated in terms of its ability to withstand a seismic event because of its “proximity to Toronto.”

The earthquake June 23 measured 5.0 on the Richter Scale. The epicentre was about 60 kilometres north of Ottawa, but the quake was felt all the way down to New York City.

There were no injuries and reported damage was minor. Structural engineers were called to eight Ottawa elementary schools to ensure they were safe for occupancy.

Dr. David Allen, an engineer and former guest researcher at the National Research Council, now retired, says standards for retrofitting buildings to better withstand seismic events were last updated in 1990.

“Even then, we relied on what the U.S. had done ,because they had a lot more information and experience with this,” he says. “We should be looking at this again.”

Still, he says, retrofitting is expensive and places an undue burden on owners who sometimes can’t afford to replace or retrofit.

He says the National Building Code sets out expected seismic ground motions and their magnitude in various regions of Canada with 10 per cent probability of occurring once in 50 years up to a magnitude 6.0.

“Since 2005, the Code is pretty good,” he says.

“The problem is with older buildings, especially masonry, which gets very brittle.”

Dr. Dan Palermo, assistant professor and structures lab manager at the University of Ottawa’s Department of Civil Engineering said there’s always room for improvement, especially when it comes to older structures.

“There is a fairly new initiative — the Canadian Seismic Research Network — in which we are looking at older structures and look at the question of retrofitting buildings pre-1970s,” he says. “Some buildings in Ottawa have been retrofitted, but it’s not on a grand scale. Events like the earthquake here bring more attention to it.”

Future standards, he says, will likely focus more on performance-based design.

“Currently the standards suggest a building will suffer some non-structural damage in an earthquake and some structural damage in a major earthquake, but not collapse,” he says.

Performance-based standards allow for a design to survive specified seismic events without structural damage.