The Macdonald Bridge redecking project is starting, with its attendant closures and traffic diversions. By all appearances, the bridge commission is proceeding in a manner to minimize disruptions as much as possible, and we’ll all simply have to have patience and bear with it. Life goes on.
But why does the bridge need redecking anyway? The Macdonald Bridge opened on April 2, 1955, and so is 60 years old. That’s not particularly old, as suspension bridges go. The third car traffic lane and bike and pedestrian lanes were added in 1999, which added to the weight of the structure, but that isn’t particularly unusual either. Here’s a quick scan of a handful other North American suspension bridges:
Golden Gate Bridge— opened in 1937. Major reconstruction in 1986 (more on this below).
San Francisco–Oakland Bay Bridge—opened in 1936. Rail service removed from lower deck in 1960 and replaced with road traffic. A portion of the upper deck collapsed in the 1989 Loma Prieta earthquake, which led to the reconstruction of the eastern span of the bridge, but not the suspension portion of the bridge.
Brooklyn Bridge—opened in 1883. The approach ramps to the bridge were replaced in 2010, and renovation of the main span begins next month, but the renovation is not as extensive as the complete redecking the Macdonald is undergoing.
Delaware Memorial Bridge—first span opened in 1951, second span in 1968. An upgrade to both spans was completed in 2008, but neither required redecking.
George Washington Bridge—opened in 1931. Two lanes were added in 1946, and a lower deck added in 1962. In 2011, the Port Authority of New York and New Jersey began a billion-dollar project to replace the vertical ropes connecting the cables to the deck, but the deck itself remained in place.
St. John’s Bridge (Oregon)—opened in 1931. A redecking project was completed in 2005.
Tacoma Narrows Bridge—opened in 1950. The Tacoma Narrows Bridge replaced one by the same name, seen in the video above. It opened, and collapsed, in 1940. The engineers weren’t about to let that happen again, and I bet the 1950 bridge is among the sturdiest bridges on the planet. A parallel span was opened in 2007.
Lion’s Gate Bridge—opened in 1938, Lion’s Gate was designed by Monsarrat and Pratley, the same firm that designed the Macdonald Bridge. Lion’s Gate was owned by the Guinness family, of beer fame. They sold the bridge to the province of British Columbia in 1963. Lion’s Gate was redecked in 2000 and 2001, when the bridge was 62 years old, about the same age as the Macdonald is now.
In 2009, Darryl Matson, an engineer with Buckland & Taylor Ltd, presented a paper titled “The Lions’ Gate Bridge Suspended Span Replacement” at the Transportation Association of Canada conference in Vancouver. In the paper, Matson was straightforwardly blunt about the reason Lion’s Gate needed to be redecked:
Constructed in 1938 to a brilliantly light design, the bridge was privately financed. As such, long term durability was often sacrificed in favour of initial capital cost savings.
The bridge was initially opened with two traffic lanes, and the only concession the developers made to the future was to design the bridge deck such that three narrow lanes could be squeezed between the curbs.
By the early 1970’s, the durability of the bridge had become an issue. The concrete deck of the 669m long north approach viaduct to the bridge had deteriorated to the point where the Government was repairing more than 1,000 pot holes per year.
By the mid 1990s, the bridge was carrying 70,000 vehicles per day. Due to the heavy traffic, and the economy of the original construction, the suspension bridge deck had deteriorated to the point where maintenance was costing approximately $3 million per year.
I’ll take Matson at his word: Lion’s Gate needed redecking because long-term durability was sacrificed to save money.
Is that the same reason the Macdonald Bridge now needs redecking? Was Monsarrat and Pratley going around low-balling construction tenders to get the jobs done on the cheap, rather than build for the long-term?
Jon Eppell, the bridge engineer on the Macdonald Bridge, told me today me he knows Matson but hasn’t read his paper. “But I agree, for sure, they built [Lion’s Gate] on the cheap,” said Eppell. “To give you one example, I’ve seen a profile of the bridge, and at the middle of the bridge it actually comes to a point, instead of a nice curve.”
“But, that’s not really true of the Macdonald Bridge,” continued Eppell.
Contrary to what I learned in my morning of surfing the internet, Eppell told me that bridges are redecked frequently, just not in as dramatic a fashion as the redecking of the Macdonald. The Golden Gate Bridge, for example, was redecked in 1986, one lane segment at a time, while the bridge remained open.
Eppell said the Macdonald deck is built “of floor beams and stringers, all of which are I-shaped beams,” and there’s corrosion where there vertical wires meet the beams. This appears to me to be qualitatively different problem than the redeckings I’ve read about.
I asked Eppell why the bridge is closed at night now, when the bike and pedestrian lanes won’t be removed until June and the first deck segment not lowered until later in the summer. He explained that because the redecking will shift the load of the bridge in different directions as each new deck segment is put in the place, the new support trusses have to be added. And before that can be done, crews have to strip the lead paint; they are now measuring and marking what has to be stripped — you can see the orange marks on the bridge now.
Eppell is the project manager for the redecking. It’s the largest construction project on the bridge since it was built — when five people died. I asked him if that weighs heavily on him.
“Well,” he said, “they did things differently back then. They actually said, ‘a project this size, we’ll lose five workers.’ Now, we plan for no deaths, and no injuries. Safety is our first concern.”