June 25, 2007

Standards

Seismic standards for steel frames to be reconciled

PETER KENTER

correspondent

The 2005 National Building Code of Canada introduced substantial technical changes over the previous edition, including a new subsection on Earthquake Load and Effects. The Canadian Standards Association (CSA) addressed the same seismic concerns through standard CAN/CSA-S16-01 but with slightly different terminology.

The CSA issued S16S1-05, a supplement to the standard, to help reconcile the differences but some uncertainty remained.

“The National Building Code (NBC) is objective, while the CSA is prescriptive,” says Mike Gilmor, president of the Canadian Institute of Steel Construction (CISC). 

“There’s still some confusion as to how to decipher the code and standards to ensure that the terminology people use can be associated with the proper steel framing technology.”

For example, when the CSA refers to “direct-acting steel bracing systems,” the NBC refers to the same system as “non-chevron braces.”

Even within the NBC itself, some changes have required major adjustments in the building community. Whereas static method testing was once considered optimal, for example, dynamic analysis is now the preferred test method.

The CISC has issued a number of bulletins and offered a series of two-day intensive seminars to help building practitioners sort out the changes as part of what it calls a “seismic roadmap.”

“We’ve had a record turnout for these,” says Gilmor. “The audience is largely made up of engineers, detailers and fabricators.”

Gilmor notes that with the vast number of configurations available to create seismic-force-resisting steel-based frames and the differing risks of a seismic event in various locations across the country, some choices that satisfy the NBC aren’t necessarily the most economical ones.

“Designers shouldn’t rely on their past experiences to find the best solution,” says Gilmor. “With all of these changes, we need to take a fresh look at the underlying framing decisions to be made by designers.”

Print | Email | Comment