After years in the design and planning stage, the re-decking of the 762-metre suspension section of the Macdonald Bridge over the Halifax harbour between Dartmouth and Halifax, N.S. is poised to start in earnest this summer.
The new steel deck will be installed in 46 panels or sections — each one hoisted into place from a barge in the harbour with a lifting gantry and strand jacks. The old panels will be lowered on a hoist to barges and hauled away.
Construction is expected to cost about $150 million, with the total cost, including planning and design of the multi-year project running about $200 million.
As it stands, the bridge is safe, but after 60 years the steel deck is wearing out and repairs aren’t an option, says Senior Engineer Jon Eppell of Halifax Harbour Bridges (HHB), the provincial commission overseeing construction and maintenance of the landmark crossing.
There is corrosion in inaccessible points where the deck meets the floor beams that is "pushing the deck up," resulting in a bumpy ride for motorists.
The erection — coined "the big lift" — will be done by American Bridge Company. The first panel will be erected from the harbour in August with the final section to be installed in 2016.
Eppell says the first section will be among the most challenging to install partly because of the tight location against cable bent legs and an existing segment. The old segment will have to be "angled" out of its position and removed.
"The first four or so segments will be done on weekends until they (American Bridge) can get their timing down to 10.5 hours per segment."
He says it has taken about four years from the time of conception to actual construction of the deck panels. In addition to the deck installation, additional construction is expected to be completed in the fall of 2017.
Cherubini Metal Works Limited of Dartmouth is fabricating the 46 panels or sections, each weighing about 150 tonnes and roughly 20 metres square. Each panel will take about a week to complete, says Steve Ross, general manager, Cherubini.
"This is probably the largest single project we have ever done from a dollar and man-hour perspective," says Ross, adding it is only the second suspension bridge in the world to have its deck replaced while remaining open for traffic. The first one was the Lions Gate Bridge (its sister bridge) in Vancouver.
The replacement deck covers three lanes and a sidewalk/bikeway.
After the steel fabricator was awarded the job last summer, it "went through a lot of capital (more than $6 million) to set up for the project," says Ross. That outlay included welding gantries and two 30 x 40-metre insulated temporary enclosures to house each deck panel or section for sandblasting, followed by a three-coat paint application comprised of a zinc primer, epoxy mid-coat and urethane topcoat.
Cherubini also had to build a million dollar custom rib-bending machine. The steel ribs form part of the deck system which includes trusses underneath the steel plate deck, says Ross.
A durable non-skid epoxy-based surface will then be applied to the panels at Cherubini’s wharf facility to act as a temporary road surface until the new bridge deck is completed and a permanent asphalt surface can be laid, says Ross.
Watermain pipes and some electrical will also be installed at Cherubini’s wharf prior to the deck sections being transported by barge in the harbour to the bridge for erection.
Ross says Cherubini has done other work on the big bridge, including decking on the non-suspended span of the third lane and decking for the approaches in 1999.
The steel company does fabrication and erection typically for about eight to 10 smaller bridges a year in Nova Scotia and other provinces.
"This bridge project is more innovative and complex than others we’ve done, but it is certainly within our ability."
Eppell says the new deck will be 2.1 metres higher than the old one, which is about 50 metres above the harbour.
The raised deck will improve "the margin of safety" for the largest cargo ships, he says. "Some of the vessels come within 1.2 metres of the bridge now."
To raise the deck, each panel or section will be slowly jacked up about six inches. The process will be repeated until the new deck height is reached. The work will take about two months and be performed by American Bridge, says Eppell.
Planning the deck replacement project began in 2010. The work is an engineering design by Buckland & Taylor Ltd. (which also designed the deck replacement of the sister crossing — the Lions Gate Bridge in Vancouver in the late 1990s) and Harbourside Engineering Consultants of Halifax.
The 1.3-kilometre suspension bridge opened in 1955.
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