Even the most experienced steel erector faces a project with a new twist or two now and then. A case in point is a job at Toronto’s Yorkdale Shopping Centre done by Benson Steel. The challenge: how to safely and practically transport nearly 30 tonnes of steel girder over a 300-foot stretch atop the roof of one of Toronto’s busiest shopping malls.
“We’ve never done anything at that reach that deep into a building before,” says Len Giangregorio, senior project manager, Benson Steel.
“Usually there is a way you can get a crane into a building but on this one we had to reach over top of the roof for a distance of 308 feet.”
The 111-foot girder, which is 63 inches deep by 20 inches wide, was required when a multi-million expansion at the mall called for a new escalator to the third floor at one of its food courts. To increase headroom for the escalator the existing roof and trusses had to be cut away and replaced with the new welded wide flange girder.
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To complete the job, a 600-tonne Demag AC 500-1 crane with a 308-foot radius was used. The girder was fabricated in three segments, each erected separately one foggy night in November.
To balance the crane’s boom, an 80-tonne counterweight was required. The crane was supplied by Mammoet.
After considerable planning and coordination the erection process took only about four hours to complete. It was done after 11 p.m., long after shoppers had left the building. For additional safety, a section of the mall under the travel path of the large girder was cordoned off.
“There is really no protection you can put on a roof for a girder that big,” says Giangregorio. “It’s a job that could have been very complicated but it went very smoothly.”
A week prior to the erection, the existing roof deck was removed and the building’s structural steel was prepped to support the new girder. A temporary shoring tower was built to carry the additional load of the new girder during installation.
One end of the existing steel column was reinforced from the basement up with “stiffener plates” to carry additional loads posed by the new girder, the engineer says. A five and a half inch thick steel pad was installed on top of the column.
The opposite supporting end of the existing concrete beam was sandwiched between two 18-inch deep channels for reinforcement. Another five and a half inch plate was installed atop the beam to support the girder. One-inch bolts fastened the connection plates together, explains Giangregorio.
Two of the girder’s three sections were 40-feet long, each weighing 10 tonnes and one was an eight-tonne 31-foot segment.
To keep the building watertight, Carillion Construction, the project’s general contractor, erected a temporary wood structure to cover the opened roof deck during the operation. “They made it in sections so one section could be removed to allow for the placement of each section of the new girder,” says Giangregorio, adding “it looked like a long fishing hut.”
Stampa Construction, a subcontractor to Benson Steel, did the erection.
Giangregorio says the weather was on the company’s side during the operation. Even though rain was forecast on the day of the erection, none fell.
“It was very foggy but nothing we couldn’t deal with.”
Transporting the large steel element to the site and assembling the crane took longer than the erection process. At 275-feet long, the crane’s luffer had to be shipped in segments as well as the 80 tonnes of balance weights on 12 transport trucks to the site. Crane assembly took all night.
The job required approvals from the airport authority because of the crane’s height and proximity to Downsview Airport. A red beacon was installed atop the crane.
The project is part of Yorkdale’s new facelift and expansion of its retail component.
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