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Swing bridge improvements an exercise in timing

0 282 Infrastructure

by DON PROCTER

The Nova Scotia government is spending $9 million on improvements to the Canso Causeway swing bridge at Port Hastings, the Trans-Canada Highway link between the province's mainland and Cape Breton Island.
The $9-million improvements to Nova Scotia’s Canso Causeway swing bridge include replacing primary structural steel components and corroding secondary steel members, such as bracing and lattices. The replacement work will be done over the winter when it is closed.
The $9-million improvements to Nova Scotia’s Canso Causeway swing bridge include replacing primary structural steel components and corroding secondary steel members, such as bracing and lattices. The replacement work will be done over the winter when it is closed. - Photo: Nova Scotia Transportation & Infrastructure Renewal

Built in 1955, the 90-metre-long steel through-truss swing bridge has two vehicular lanes and tracks for rail traffic. The bridge, which swings open for shipping vessels passing through the Canso Canal, has allowed more than 125,000 vessels through the canal in the past 60 years.

The project, to be managed by prime contractor Allsteel Coatings Ltd. of Port Hawkesbury, N.S., includes replacement of the primary structural steel components and corroding secondary steel members, such as bracing and lattices. The replacement work will be done over the winter, the season for which it is annually closed.

Other work includes sandblasting and painting, mechanical/electrical upgrades and relocation of the operator's cabin, taken from atop the bridge to a new building adjacent to the crossing.

Will Crocker is the Nova Scotia Department of Transportation and Infrastructure Renewal's (NSTIR) engineer responsible for design procurement.

"There's going to have to be a lot of planning and co-ordination to make sure things run smoothly because we're dealing with boat, highway and rail traffic. We've never done this type of work before on a swing bridge."

Andrew MacPherson, the project engineer with NSTIR, says work will be co-ordinated to ensure that marine traffic will have access to the canal when it is rescheduled to open in spring 2017. An Acrow bridge (a portable, prefabricated steel truss structure) will be installed beside the bridge as a detour route for highway traffic during next winter to allow construction on the superstructure to be completed unhindered.

MacPherson says the detour crossing — installed on temporary foundations — will include a walkway for pedestrians. The approaches for the bridge will be built first and the structure will be assembled on the approaches and "rolled" or launched across the canal atop one foundation to the foundation on the opposite side next fall.

"Ensuring the timely installation and removal of this detour will be a challenge in itself," says MacPherson.

Work involved on the superstructure consists of repairs to truss members, floor beams and loading girders plus replacement of bottom laterals, loading beams and cross bracings, he points out.

"At any given time only a limited number of elements being replaced can be removed to ensure that the structural integrity won't be compromised," MacPherson says.

The operator's cabin on the bridge will be unbolted, cut away and removed and a new three-level concrete building with improved electronic controls and a computer system will be constructed adjacent to the bridge.

The move improves vertical clearance, allowing over-dimensional vehicles access to the crossing, says Crocker.

"It will also offer a safety improvement because the operator no longer has to climb up the bridge and across to the cabin," he states.

Crocker says despite its age, the bridge is in good condition — possibly in part because during the three seasons annually that the bridge is open it has an operator 24/7 to ensure everything is working as it should.

The last major improvement project was in the early 1990s when the concrete deck was replaced and the bridge was repainted.

Work on the bridge is based on a structural investigation completed in 2014, says Crocker.

The bridge work is scheduled to be completed in 2017.

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