June 20, 2006

National Building Code: planning for disasters

WARREN FREY

staff writer

VANCOUVER

The new national building code is toughening up the design and construction of new buildings to prepare for both disasters and every day wear and tear. But enforcing the new rules will start on the drawing board of the architects designing the structures.

The new National Building Code of Canada (NBCC 2005) was released on September 26, 2005, but it’s already in effect on federal and provincial work sites. And with a ten-year gap since the last building code revamp in 1995, new issues have taken centre stage in the revised code.

Andrew Betten, a structural engineer with the Bush, Bohlman and Partners engineering firm, said one of the most notable changes is an increased emphasis on proper seismic preparedness for a more far reaching subset of buildings, classified as “post-disaster” structures, one of four different “impact” categories.

“It’s a huge rewrite of the seismic code,” Betten said.

The other categories are “low,” a rarely used category, “normal,” which includes most residential buildings, and “high,” which until recently, included schools.

Recent disasters such as Hurricane Katrina demonstrated that in times of crisis, people will gather in public buildings such as schools and community centres, which have also been reclassified.

Andrew Betten

“However, arenas are still not classified ‘post-disaster’, even though people gathered at the Houston Astrodome after Katrina,” he said.

Besides classifying the buildings themselves, the code has also tightened up requirements regarding irregularities with buildings.

“There are more restrictions of irregularities in high seismic zones, such as Vancouver,” Betten said.

Buildings such as podium-style structures are now much more restricted, and buildings with a high amount of vertical stiffness cannot be classified as post-disaster structures, he said.

Plane discontinuity, such as parking garages that jut out past a main structure, are also facing higher restrictions, as are low ductile buildings, such as tilt-up constructions or reinforced masonry buildings.

“But that makes you wonder if we’ll have to have wooden fire halls,” Betten quipped.

Architects and engineers will have to adapt to a new emphasis on dynamic analysis.

Previous codes put static analysis front and centre, but the 2005 code makes dynamic analysis the default when determining the soundness of a new building.

“Static analysis is still permitted for buildings in zones of low seismic risk.”

The collective impact of these new changes means building forms will be altered, and the new structure restrictions will impact architectural options in high-risk siesmic zones, he added.

Seismic preparedness is not the only condition addressed by the new code. Protection against snow and rain has also been revamped, along with considerations of wind load.

Other factors, such as upwind terrain, are now included in the code.

“That’s never been done before in a Canadian code,” Betten said.

Reductions are now made in the code requirements if a structure is in suburban, urban or “rough” terrain, and hence protected to an extent from direct gusts of wind.

Exposed terrain, on the other hand, must have higher cladding loads, which also means more exterior studs, Bennet said.

“This used to be governed by deflection, but now, it’s strength control, which means more studs, and might also mean a higher stud size.”

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