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Seismic bridge design guidance to come from B.C. regulator

Peter Caulfield
Seismic bridge design guidance to come from B.C. regulator

The Association of Professional Engineers and Geoscientists of British Columbia (APEGBC) is developing professional practice guidelines for the performance-based seismic design (PBD) of new bridges.

The guidelines will provide guidance for applying the seismic PBD requirements of the new S6-14 Canadian Highway Bridge Design Code.

They will establish the standard of care that APEGBC members should follow when they design new bridges.

"Work on the guidelines is under way," said Lindsay Steele, APEGBC Associate Director of Professional Practice.

"We expect they will be completed by the end of 2017 and published in the winter of 2017-18."

The completed document, which will be called APEGBC Professional Practice Guidelines for Performance-Based Seismic Design of New Bridges in B.C., will be available free of charge on the  association’s website.

According to S6-14 Clause 4.4.6, "Performance-based design allows designers the flexibility of choosing materials, design options and construction methodologies to more accurately reflect the seismic environment and configuration of the designed structure while providing owners, regulatory agencies, designers and the public a consistent expectation of the structure performance during designated levels of seismic events."

Steele says the guidelines will be the first guidance document for B.C. professional engineers when they are involved in the seismic PBD of new bridges. (Until the guidelines are published, B.C. engineers may have to consult a supplement to the Canadian Highway Bridge Design Code prepared by the Ministry of Transportation and Infrastructure.)

The guidelines are being prepared by Steele, who is project manager, and a group of five engineers who are experts in bridges and seismic activity. Before they are published, the guidelines will be vetted by a review group from various B.C. stakeholder organizations.

B.C. professional engineers are not the only ones who can use the guidelines.

"The guidelines will also be useful to jurisdictional authorities and the general public, because they establish a common level of expectation and understanding for the standard of care appropriate for designing new bridges," said Steele.

As far as Steele is aware, APEGBC’s seismic PBD guidelines will be the first in Canada to provide guidance to engineers on how to follow their professional practice standard of care on S6-14.

"The practice of professional engineering is both broad and specific," said Steele. "APEGBC produces guideline documents on specific professional services or activities whenever additional guidance is needed. We believed it would be beneficial to establish greater clarity around the seismic performance-based design of bridges."

It’s not clear what effect, if any, the new guidelines will have on the cost of building a new bridge.

"The guidelines are intended to establish standards of practice," Steele said. "They’re not necessarily related to the direct and specific factors that can affect the cost of a bridge."

Saqib Khan, a seismic specialist on bridges and structures at the Vancouver office of Hatch consulting engineers, and the lead author of the group developing the guidelines, says PBD is not new to B.C.

"It has been in use in this province on large bridge projects for more than 10 years," Khan said.

Unlike force-based design (FBD) guidelines, which are built around prescribed levels of structural strength, PBD describes how a bridge would perform after a seismic event.

"For example, there could be minimal damage corresponding to immediate service and minimal residual displacement to a bridge," Khan said. "But a larger event could lead to extensive visible damage and bridge service disruption."

APEGBC has developed other seismic professional practice guidelines for B.C. engineers. Several years ago the association created guidelines for the seismic retrofitting of B.C. school buildings.

"The initial guidelines came out in 2006," said Peter Mitchell, APEGBC Director of Performance Practice Standards and Development. "We had been asked by the Minister of Education to develop a common approach for engineering companies for the seismic assessment and retrofit of B.C. school buildings."

If a B.C. school district wants to seismically upgrade one of its schools and it seeks Ministry of Education funding to do it, the engineering company it hires has to follow the APEGBC guidelines.

Seismic events — the technical term for earthquakes — are serious matters on the west coast.

According to the Structural Engineers Association of BC, the Pacific Coast is the most earthquake-prone region in Canada.

In the past 70 years, more than 100 earthquakes of magnitude 5 or greater (large enough to cause damage had they been closer to land) have occurred just off the west coast of Vancouver Island.

And should one take place on land, it has an abundance of targets to choose from. There are already 2,900 bridges in B.C.

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