Engineers have eliminated one of the much-heralded features of the new Johnson Street Bridge — allowing pedestrians to walk through its “open wheel” mechanism as the lift span goes up — to compensate for structural weaknesses in the bridge’s original design.
This shocking fact, revealed in the April issue of FOCUS magazine, only became apparent to Victoria’s councillors last week. David Broadland, the publisher of FOCUS, noticed in slide 24 of the March 15 engineers’ presentation that the walkway through the open wheels now appears to hang from the underside of the bridge deck, so it will have to rotate with the wheels when the bridge lifts. Broadland emailed councillors to ask if the design had changed, and councillor Geoff Young raised the question at their March 22 meeting.
“There’s been no material change in the design. The walkway through the wheel is there,” City bridge project manager Mike Lai told the council last Thursday. But the counterweight, which originally was suspended from the wheels alone, now has to hang from the bridge deck as well. “In doing so, the walkway that is through the wheels, that is still accessible, would not be in use while the bridge is opening,” Lai said. “That is also a public-safety issue as well. We wouldn’t want people to walk through the walkway while the bridge is moving.”
Councillor Young was surprised. As he noted, the always-open walkway was a selling feature of the new bridge — indeed, one of the City’s “Vote Yes” brochures for the 2010 referendum said it “will be the first bridge in the world where you can walk through the rolling mechanism while the bridge raises.” Bridge architects WilkinsonEyre made a similar promise in promotional material on their website.
Young noted that council had recently discussed the walkway, yet staff hadn’t mentioned the change — another example of the City’s managers withholding information from elected officials. But the bigger problem is that the new bridge’s price tag has already escalated to $92.8 million, and it’s still only at a 50% “design level”. “My fundamental concern,” Young said, “is us being wedded to a design that is capable of that degree of evolution at this point in the process, and the concern that raises with me about the level of uncertainty with regard to the ultimate cost.”
The City’s director of engineering, Dwayne Kalynchuk, replied: “It’s a complicated process in designing this bridge … there’s not another bridge we can go look at and say, ‘Okay, that’s how it’s developed, that’s how it’s going to operate.’
“One of the complications is the size of these wheels, and the fact that they have to provide stiffness to the wheels to carry the whole load,” Kalynchuk continued. “They decided that the way to get that stiffness is to put cross-members at the bottom — not at the top, because there is a visual element we have to maintain — and with those cross members, it interfered with the opportunity of having that revolve around the walkway. So the concept then was to say, ‘Well, let’s fix the walkway to those members.’ That’s why the whole walkway turns with the bridge. That’s why you can’t have people on it. The point I’m trying to make is, with a unique structure — Mike and I met in November with the structural engineer and the whole team — these are the challenges that they face. There are these sort of evolutions.”
Back in 2010, when we described the rolling bascule design as “something of an experiment”, the City’s lead engineering consultant swiftly rebuked us, assuring readers that the mechanism was “robust” and “tried, tested and proven”. Since then, rail has been eliminated, the length of the lift span reduced from 47 metres to 41, and the quantity of steel for the counterweight cut from 1,600 tonnes to 840 — and yet the rings still have to be shored up with cross-beams. So the original design was not quite as “robust” as advertised, and another amenity promised with the bridge project has disappeared.
The price is going up, and Victorians are steadily getting less bridge than they bargained for.
UPDATE: Watch the March 22 council meeting where the design change was first revealed (video courtesy of Modern Democracy):Tweet