September 2, 2008
When you think about the Granville Street Bridge—a bridge so much a part of the city that most people don’t think about it much, even as they’re using it—you realize that you never see big trucks on it. They’re not allowed. The bridge was never designed to take vehicles even as heavy as city buses. But Canada Line construction on Cambie means that five-axle traffic is going to have to find another way across False Creek, and so the Granville Bridge will have to pull more weight. It’s going to be strengthened, a $5-million job that will go to tender and be finished, with luck, in time for the Olympics. At least the choice of the design engineer won’t bog down the process. In May, spending less time on the item than on your average debate about dog-leashing, council voted unanimously to award the $330,000 contract to Buckland & Taylor, the North Vancouver–based bridge-engineering firm founded in 1970 by Peter Buckland, an Englishman with a passion for big bridges.
Why B & T? Well, the firm was already intimately familiar with the Granville Street icon, having worked on it in the past and having completed a study of the needed renos last year. (It’s the approach spans, and not the steel deck itself, that require beefing up with steel stirrups.) But really, it was because, well, when you need to get a Frisbee off the roof of your house and one of the people who step forward to volunteer for the job is Spider-Man, you halt the search right there.
Bridge engineering isn’t a field with a definitive king, but Buckland & Taylor sits among the elite. It has designed some of the longest cable-stay bridges in the world. The firm worked on Canada’s most ambitious bridge, the 13-kilometre-long Confederation Bridge joining P.E.I. to New Brunswick, and it has retrofitted bridges over some of the most storied landscapes in the United States—California’s Pacific Coast, the Grand Canyon, and San Francisco Bay (that would be the Golden Gate Bridge; B & T worked on its seismic upgrade). Its fingerprints are on almost all the bridges in Vancouver: it has either assessed them for ship impact, or earthquake-proofed them, or designed them outright. (Most recent is the North Arm Bridge, which will carry SkyTrains over the Fraser River to the airport.)
The firm also has a reputation for taking on the biggest head scratchers—jobs that seem to present all but insurmountable engineering challenges. (For that reason, Buckland hires for raw brainpower and creativity over experience. A young engineering grad “uncontaminated” by memories of how things used to be done is more likely to come up with novel solutions.)
B & T’s finest hour came in the late 1990s. The Lions Gate needed to be stronger and wider, but there were strict conditions for replacing the deck: it had to be done without disturbing the heritage details. And, oh yes: without closing the bridge to daytime traffic—something that had never been done. (The Canadian Council of Professional Engineers called the job, when it was completed in 2002, “a miracle.”)
“That was tricky,” Buckland admits, with typical understatement and in the cut-glass accent of his native London, during a walk across the Granville Bridge. Buckland is a tall, refined man, with bird’s-nest eyebrows. Studying engineering at Cambridge (he graduated in 1960), he had no specialty in mind until “I realized I was going to have to work for a living, so I thought I’d better do something I enjoyed. And bridges seemed kind of neat.”
Bridges are neat, and in a water city like Vancouver, where Buckland arrived and hung out his shingle in 1963, they’re something like vital organs. The Lower Mainland’s bridges, which are arguably more recognized than its buildings, run the gamut from suspension (the Lions Gate) to cable-stays like the Alex Fraser (the longest of its kind when it opened) to Granville’s steel-weld truss to the tied-arch design of the elegant Port Mann. You could conduct a survey course in bridge engineering right here—and a couple of years ago Buckland did more or less that, squiring two busloads of visiting colleagues on a tour of the city’s bridges.
Buckland crosses a bridge differently than you or I might. He doesn’t look so much out off the deck as down and almost into it. “Can we see deterioration here?” he says, peering closely at the concrete on the Granville Bridge’s south approach. “There’s a crack.” Cracks in concrete are okay. Cracking is, in fact, what concrete is designed to do. “But it does let the salt and water in, slowly. Over time the reinforcing steel inside the concrete corrodes.”
And so a bridge wears out by vanishingly small increments. “This bridge has been here for 50 years now, but in another 100 years it won’t be here.” How long is a bridge supposed to last? “The Canadian code requires a life of 75 years,” he says. “The British code requires 120.”
Bridges end their life in three ways. They become functionally obsolete. “Cambie is an example,” Buckland says. “There was a bridge there before, but its job changed and now we have another.”
Or they are declared “structurally deficient,” meaning wear and tear has made them too dangerous to keep open.
Or they collapse. Which, if you’re a civil engineer in a city near a major fault line, is a scenario that turns perpetually in the subconscious mulch. On October 16, 1989, Buckland & Taylor signed a contract with the City of Vancouver to study the earthquake capacity of the city’s bridges. Twenty-four hours later, a 6.9 earthquake struck Loma Prieta, California, collapsing the Bay Bridge and killing 67 people. It was a turning point in bridge engineering and spurred worldwide retrofitting.
Buckland looks down, beneath the bridge deck. Many things have been done to make the Granville Bridge strong yet flexible. A couple of the piers are wearing metal cylinders. “In a severe earthquake the concrete kind of turns to rubble,” he says, “and then the reinforcing steel inside it just sort of buckles outward and the whole thing collapses. That wasn’t known when this bridge was built. But now, if the concrete crumbles the pier will hold.”
He points out a grey patch at the top of a column. “That’s a wrap of very high-strength glass fibres that keeps it all together but doesn’t make it stiffer. It had been done experimentally in California. As far as we know this was the first time it had been done commercially.
“There are energy absorbers under the piers—crescent-shaped plates—and they’re like paper clips: they bend and then they bend back. And there are cables down there to make sure the superstructure doesn’t fall off the pier, even though you’ve absorbed the forces.”
How big an earthquake could the Granville Bridge withstand?
“We kind of don’t do it on the Richter scale, because that’s a measure of damage—it doesn’t tell you what the forces are,” Buckland says. “We’re designing for an earthquake that would recur every 450 years. And it wouldn’t fall down on that. And that’s big.”
It’s not productive to talk about fate, so engineers generally don’t. “The fact is,” Buckland says, “we’re safer standing here on the Granville Bridge than we just were in your car, by a factor of about two thousand.”