New span built to top quake standard: staff

Victoria councillors were reassured March 12 that the new Johnson Street Bridge is being built to the highest possible seismic standards.

“The design of the new bridge means this bridge will be available to all traffic — not just emergency traffic — all traffic after a one-in-1,000-year earthquake,” Jonathan Huggett, interim project manager, told councillors.

Further, Huggett said he’s been assured by the city’s consultant MMM Group and subcontractor Hardesty Hanover that the bridge will be available for use by emergency vehicles and Department of Defence vehicles after a large earthquake, such as a “one-in2,500-year return period event.”

The return period is an estimate of the likelihood of an event. It is based on historical data and gives the average time between an event such as an earthquake and the next occurrence of an event of the same type or intensity. A larger return period implies a larger earthquake.

“I don’t know anywhere where anyone is designing anything higher than this,” Huggett said.

“If this is wrong, then I would suggest that we have a bigger problem than that because every other bridge that has been recently constructed in British Columbia has been designed to that standard.”

Mayor Lisa Helps asked for the update after a local media outlet raised questions about the seismic vulnerability of the new bridge, reporting that it could be permanently knocked out of service by a magnitude-7.5 earthquake, which has a 30 to 35 per cent chance of happening in the next 50 years. The report said the lower seismic standard was used to reduce costs and would be a much lower level of seismic protection than the city had requested in 2010.

In response to a question from Coun. Marianne Alto, Huggett said that wasn’t the case.

“This is the highest standard that people in this area are constructing bridges to. We have not somehow gone to some kind of lower standard to save money,” Huggett said. “In fact, I don’t know how that would have even come into the mix.”

Huggett said there would be no motive for someone to reduce the design standards.

“H&H and MMM are not responsible for the final construction costs of this bridge. They designed it. So if it turns out it costs more money, it’s not their problem. PCL [Constructors] didn’t design the bridge. They have the contract to build it and they’ll build whatever they are told to build,” Huggett said.

“So, I’m at a loss to understand who might have suggested reducing the standard and what possible advantage they would have got out of it.”

At the suggestion of Coun. Ben Isitt, Huggett was asked to report back on an apparent discrepancy between his assertion that the bridge should withstand a one-in-1,000-year seismic event and a 2012 MMM report. That report said the bridge should withstand a one-in-475-year event, but there could be a risk of permanent failure in a one-in1,000-year event.