By Bronwen Parsons, Editor
Italy earthquake prompts questions about Canada’s seismic codeBuildings Codes Seismic design
Following the earthquake that killed approximately 290 people and destroyed the historic centre of Amatrice and other medieval centres in central Italy last week, the authorities are asking questions.
According to media reports some of the buildings that collapsed, including a school and a medieval bell tower, had been seismically retrofitted in the past few years following an earlier earthquake in the Appenine Mountain region. Retrofits to the elementary school that crumbled last week, for example, had cost US $785,000.
Now prosecutors are asking whether negligence or fraudulent construction practices contributed to the devastation, since these seismically reinforced structures did not stand up to the 6.2 magnitude event. The quake has displaced thousands of people, destroyed homes and apartment buildings, and wrecked churches, town halls and cultural treasures dating back hundreds of years.
Asked for comment, Tibor Kokai, Ph.D., P.Eng., a principal of Read Jones Christoffersen, says: “The school that collapsed in Italy was retrofitted, so whether they overlooked something, nobody knows.” Kokai co-authored the Concrete Design Handbook and is a member of the CSA A23.3 and past member of the Standing Committee on Earthquake design. He has designed tall buildings in cities across Canada and is currently designing two 100-storey buildings in Toronto.
“Different codes in different countries specify the different levels of earthquake to design for,” he says, “and if you perfectly design by the code, and if the magnitude of the earthquake does not exceed what you were supposed to design for, then the building should not collapse.” In short: “If we do things right and construct the building right, then it should stand.”
When it comes to retrofits, however, and here he is speaking about Canada, Kokai has concerns. The National Building Code of Canada (NBCC) allows special provisions for “grandfathering” buildings based on their past performance. It means that existing buildings only have to be upgraded to meet the latest seismic safety codes if there is a change of use, or if the owner is adding storeys to the structure, i.e. adding mass. If there is no such change and basic checks are done according to the NBCC, then the structural engineer only needs to ensure that the building will withstand 60% of the earthquake loads specified by the current codes. That, Kokai says, leaves the building “by definition 40% weak.”
The grandfathering provision in the building code is based on past performance, but Kokai says this is not fully valid. “When you say a building performed well for in the last 100 years, it is for gravity loads that are pushing downwards and some wind load action. But did this building ever experience the maximum design earthquake, which acts horizontally? No. So grandfathering the earthquake performance of existing buildings based on the last 40 years of past gravity and wind load resistance thereby reducing the acceptable earthquake resistance capacity by 40% and claiming the building is o.k. is not right.”
“While one obviously cannot upgrade the earthquake resistance of existing buildings at every code cycle,” he says, “one should consider a more stringent earthquake upgrade that exceeds the current code requirements for public buildings when other significant infrastructure improvements are happening, like upgrades of their cladding, electrical and mechanical systems.”
“There is another very important thing,” he says. “In earthquakes what kills people is not necessarily the structural collapse. Old cladding can fall down. The partitions fall over, the bookshelves fall over, the interior partitions collapse. This is what kills the most people.
For this reason he believes the heritage conservation approaches of Canadian cities are problematic. “I have done projects in Vancouver, Calgary, Montreal, Toronto. Their rules are extremely rigid. … You may want to preserve the sweat equity of the workers of 1929, but at what point are these buildings dangerous for people? At what point should red brick be totally replaced? Yes the new material doesn’t look old, but it won’t kill people.”
In Italy prosecutors are asking whether poor construction practices have contributed to the damage. Kokai explains how poor construction quality can impact the building’s integrity: “When the structural engineer specifies the amount of reinforcement, the quality of concrete, and the reinforcement arrangement, then it has to be placed exactly this way because then it meets codes and it works. If the contractor hasn’t placed the reinforcement correctly, and there was no proper site review during construction, then things can go wrong.”
“You can have a column, with vertical reinforcement, for example. If you don’t tie them together with hoops, with ties, the vertical bars will buckle. They just pop out. So, it’s a very simple thing. Have they properly installed the stirrups, the ties in the column? Have they used the proper concrete or bought something cheaper and nobody saw. If I specify 45 MPa concrete and somebody delivers 25MPa, the capacity has come down almost 35%. ”
“It’s not just an issue with high end complex jobs; if a building has a damper, then trust me, everybody pays attention because it’s a complex building,” he says. “The problem is in the two, three, four storey buildings, where you might think: “Oh, it’s a run-of-the-mill job, don’t worry, the contractor will do it right.” And at the end they don’t do it right by mistake — or deliberately: that’s another story.