January 23, 2013
Steel box girders key to new Keele Street Bridge
Steel box girders were the structural and cosmetic material of choice for the Ministry of Transportation for the construction of a new 112-metre-long, three-span Keele Street Bridge in northwest Toronto.
Soncin Construction is the general contractor overseeing the $17.1-million, two-year project which is scheduled for completion in October 2013. The consultant is URS Canada, and North Bay-based Central Welding is the girder fabricator/erector.
Spanning over and connecting with the almost constantly busy Highway 401, the existing six-lane (three westbound, three eastbound) 1965 structure is already one of the most heavily used bridges in the city.
With infill growth and the construction of the 1.6-million-square-foot Humber River Hospital on a site directly across from the ministry’s own headquarters, it will be even more heavily used.
Not only will a new left turn into the hospital be required, a cost study indicated it would be less expensive to build a new structure than continuously rehabilitating the old one, says ministry senior structural engineer Vlado Dimitrovski.
“We want the bridge opened before completion of the new hospital,” he says, in explaining why the box girder system was selected.
“Box girders are fabricated off site and lifted into place. There are fewer pieces to erect compared to I girders and less complex formwork is required.”
Besides being “more aesthetically pleasing,” they’re also shallower, ensuring ample clearance for traffic passing underneath on Highway 401, he explains.
As the old bridge has to remain partially open at all times, its replacement is being built in stages.
That sequencing also includes the installation of its five 1.5-metre-high, 112-kilogram trapezoidal girders.
Each girder is comprised of five sections which have to be lifted into place and then bolted together, says Dimitrovski.
In a careful managed sequence over three nights in the summer of 2012, the first two girders (on the west side) were inserted.
As the Highway 401 collector lanes had to be closed, it was an operation requiring careful planning and co-operation between the contractor, Central Welding, the Ontario Provincial Police, and other agencies, says Dimitrovski.
“Working over 16 lanes of traffic (on Highway 401) is always a challenge,” says Soncin project manager Clyde Crocker.
Besides the inconvenience to drivers, the lane closures impacted two other nearby ministry construction projects.
To minimize that inconvenience, a considerable amount of pre-erection work, such as placing the bolting mechanism on the girders, was done by Soncin and Central Welding, he says.
The central girder is scheduled for installation in April, with the remaining two later in the year, says Crocker.
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