For background on the Johnson Street Bridge project, we are posting relevant articles from our old website. This article, from October 24, 2010, was also published in Monday Magazine — which prompted a letter (reprinted below) from MMM's Joost Meyboom, asserting that the design of the new bridge is “tried, tested and proven”.
The attention came because Cowing, a prominent Cleveland engineer, had previously registered his design for a new type of bascule bridge [drawing at left] – in which the hinge point would be a huge wheel, turned by a cradle of gears and bearings – and this was his chance to put it to the test. Cowing opened his rolling bascule bridge with great fanfare in 1907, and went on to a good career in Chicago, where he died in 1926.
Alas, Cowing’s patent wasn’t quite so successful. In 1916, an international congress said his bridge “ha[d] not commended itself for further adoption,” and others like it were never built. Although the Cleveland bridge continued operating, by the 1940s it had become a mechanical nightmare. Due to the stresses on its bearings and gears, the bridge repeatedly broke down, often closing for weeks at a time as Cleveland frantically machined new parts from scratch. In 1957, the city finally decommissioned it, deciding it wasn’t worth the ongoing headaches. (To see some old news clippings about the bridge’s problems, click here.)
Earlier this month, the City of Victoria rolled out its $50,000 taxpayer-funded campaign to convince residents to vote in favour of borrowing $49,200,000 for a new “one of a kind” Johnson Street Bridge, to be “built for the next 100 years”. But as Cowing’s bridge should remind us, a novel design does not always live up to long-term expectations.
But was novelty a good criterion to use for a structure that’s supposed to last 100 years? Recently, I spoke with a veteran movable bridge engineer who had seen plans for Victoria’s bridge, and its rolling-bascule design “raised questions” in his mind. “I don’t see any great advantage to it,” said the engineer, who asked to remain anonymous.
The Canary Wharf bridges are only 23 metres long, whereas the lift span of Victoria’s bridge will be 57 metres long and at least 30 metres wide. Will the larger size magnify any issues with the mechanical design? “Greatly,” the engineer said.
“They’re going to need a lot of counterweight,” he continued. “What I’ve seen of Victoria, you’d have to have it extended quite a distance.” The separate pedestrian and multimodal pathways hanging off the lift span will further increase its complexity. “If you’re going to do this, it’s going to take a lot of engineering work.”
(That work will be even more complicated if rail is included, as the weight of a train demands a far stiffer span. On October 13, the Capital Regional District endorsed the City’s application for federal gas-tax money to help pay for rail on a new bridge, but Victoria’s council won’t decide whether to include rail until December, and the gas-tax application won’t be heard until April – making it hard to know whether we’re voting on a bridge with rail, or not.)
This is encouraging, but it still suggests that we’re considering a mechanism that’s unique for a bridge. The existing Strauss bridge certainly has its own issues – its hinges can’t be replaced without dismantling the structure, which MMM said would be required to give it another 100 years of life – but at least it has functioned for 86 years without significant failures. According to engineers, the typical warranty on new bridge construction lasts one year from opening. [2017 note: the new bridge has a two-year warranty.] So, if a decade from now our “one of a kind” bridge requires ongoing and expensive repairs, well, that’s our problem.
Certainly, engineering has changed dramatically since Cowing’s day, and computer-aided design has enabled the construction of some remarkable machines. But if someone tried to sell me a new car that’s “one of a kind” – and then promised, even though there are no other examples of it, that it would last for “100 years” – I’d be inclined to look for another dealership.
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