Neither motorists – nor salmon – had the chance to notice that the Capilano River Bridge was being moved.
Moving a 1,200 tonne bridge without people noticing is difficult. But that’s exactly what Murray Johnson and his engineering team from COWI Bridge managed to do last summer. While most residents of Vancouver were sleeping soundly on 19 June 2010, the team supervised the move of the Capilano River Bridge – a two-lane steel truss bridge which is crossed every day by about 25,000 vehicles.
“This isn’t the first time a bridge has been moved this way, but Capilano is unusual because it’s smack in the middle of an urban area,” explains Johnson.
In 2009, the B.C. Ministry of Transport and Infrastructure (BCMOT) had studied the Capilano River Bridge and found its steel trusses had deteriorated and were beyond economical repair. In addition, the lanes were too narrow, pedestrians and cyclists were poorly accommodated, and a transit-only lane was badly needed. The ministry contacted COWI Bridge to study replacing the bridge without disrupting traffic during construction.
There was a hitch though: the Capilano River, which gives the bridge its name, is home to several species of salmon for much of the year. Construction crews can only work in the river from July to September – a period known as the “fish window”. To carry out work in the river for the new bridge in the summer of 2010, construction crews would have to complete any advance work during the summer of 2009.
Johnson admits he and his team “did a lot of head-scratching” but were eventually able to design a way to move the bridge using a so-called truss sliding technique. “That way we could keep the old bridge and use it as a temporary detour while the new bridge is being built,” says Johnson.
Nearly a year of planning went into the operation. A temporary pier and abutments were built during the fish window in 2009 to receive the old bridge on its new alignment. The bridge move was required to be completed in June so that work in the river could take place in the 2010 fish window. Every calculation was triple-checked, says Johnson, and back-ups of every piece of crucial construction equipment for the sliding were ordered in case of mechanical failure.
“We knew we had only one shot to get it right,” he explains.
We Have Lift-Off
Johnson recalls an atmosphere similar to a rocket launch when the night of the move arrived.
First, construction crews closed the old Capilano River Bridge’s two westbound lanes and rerouted traffic to one lane of the parallel eastbound bridge. Then came the moment of truth: with the bridge closed, the contractor activated hydraulic jacks which lifted the 1,200 tonne bridge and lowered it onto steel tracks. Small greased Teflon pads attached underneath the bridge helped reduce friction coefficients to about 5 per cent.
“This way, relatively little force was needed to achieve what we call ‘the break-free force’,” explains Johnson. Then other hydraulic jacks begin the task of pulling the bridge upstream. The detour route was not exactly parallel to the original road, however, adding an additional element of complexity. “We actually swung the bridge in a small arc with the western end moving 11 metres and the eastern end 17 metres.”
Despite the air of anticipation, all the planning paid off, and the entire sliding operation was completed in six hours. As the sun came up, the road crew could remove the roadblocks and open the road before the morning rush hour.
“In the end, it was almost anti-climatic, because everything went according to plan,” says Johnson.