July 4, 2012
Sky bridge lift successful at Concord Adex condos in Toronto
Plans to hoist a sky bridge spanning two condominium towers in Toronto recently took more than three-and-a-half years of planning.
The 328-tonne bridge now connects two towers, Block 26 and Block 29, part of the Concord Adex development known as Parade. The lift of the structure was engineered by Western Mechanical Electrical Millwright Services Ltd. of Barrie, Ont.
“Construction manager PCL Constructors Canada Ltd. called us in very early in the project as part of an integrated design process,” says Mark Carney, a structural engineer with Western Mechanical. “Anyone potentially involved with the project came to the table early on so they could present the input necessary to complete the project successfully.”
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The sky bridge is three storeys tall and connects the buildings at the 33rd floor and above. Billed as the world’s highest residences on a bridge, the feature will provide residents of the two units with a one-in-a-million view of both the lake and the city to the north. A common area will also run the length of the structure.
The design of the bridge, developed by structural engineers at Halcrow Yolles, a CH2M HILL company, incorporates expansion joints and bearings similar to those used in highway bridge construction, to accommodate any wind movement between the two towers. The bridge was built in sections off site by Walters Group of Hamilton, and then assembled at the project site at ground level.
“We presented PCL with a plan to use strand jacks to lift the bridge into place,” says Carney.
“To do that successfully, Walters arranged to have steel beams fixed to the concrete pedestals in the mechanical penthouses of both buildings and we pre-determined the load needed to place on the strand jacks.”
Two fixed steel beams were installed in the square building, Block 26, while a single pivoting steel beam was installed in the round building, Block 29. The steel support beams are too heavy to remove from the building, so they’ll remain permanently in the building on the mechanical floor.
Western Mechanical representatives had increased their presence at the site since March. Three strand jacks, each capable of lifting more than 200 tonnes, were delivered to the site two weeks ago and fixed to the extended steel beams.
“At that point, the bridge was pretty much assembled,” says Carney. “Flynn Canada Ltd. was putting the finishing touches on the bridge by installing glass and insulation and electrical work was also being completed. We decided early on that the floor of the bridge would be poured only after the structure was lifted into place, to reduce the load. A vertical concrete pump line was installed along Block 26 to pump concrete into the bridge later on.”
The lift began on the night of Monday, June 26th at 11:30 pm. Because the bridge spans two buildings entirely on private property, no roads were closed. Only a pedestrian walk was declared off limits for the duration of the operation.
“You can never have a perfect situation with wind, so we provided extra stability with the use of four cranes on the ground, supplied by ALL Canada Cranes & Aerials, Limited,” says Carney. “The high capacity cables were anchored through a ballast and snatch block installed on the ground, then fed up to the corners of the bridge and tensioned.”
A Western Mechanical operator initiated the computer-controlled strand jacks to lift the sky bridge slowly into place, carefully monitoring the loads on each jack to ensure a level load. The four ground-level cranes also monitored the tension on each cable.
“To nestle the sky bridge in place against the square building, the pivoting beam rotated the other end of the bridge into place against the round building,” says Carney.
“Walters then shimmed the bridge and welded the shims into place.”
The operation was completed in 12 hours. Carney himself was called back to the office just before the piece de resistance.
“I missed the last part,” he says. “But we planned the job carefully — I knew it was going to be a great success.”
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