February 2, 2011
DOMENIC CHERUBIN / M&G STEEL
Steel sequence a challenge on Bramalea City Centre project
Renovation and expansion projects often come with the challenge of how to complete the work while existing facilities remain fully operational. That was the case at the Bramalea City Centre Mall where a new two-storey expansion and new five-storey parking deck presented plenty of complications for construction manager Vanbots Construction and its subcontractors.
“It wasn’t a straightforward job by any means,” says Brian Thompson, project manager with M&G Steel Ltd., the steel fabricator/erector. While a sequential steel erection process is the standard method of operating at most new construction projects, at the mall that wasn’t possible. M&G Steel met with delays and obstructions throughout the job that prevented a logical sequencing process.
The mall expansion was done in two phases requiring 1,850 tonnes of steel — “a pretty good sized job,” says Thompson.
In the first year of the two years, M&G Steel was on site, there was no mechanical contractor to provide dimensioned information on where to locate mechanical-related steel pieces, says Thompson.
Another hurdle, he says, was contaminated soil discovered during excavation. “We had up to 45 truckloads of steel fabricated that had to wait in our yard nine months because of the remediation.”
The expanded mall required a new structural steel mechanical plant constructed prior to the demolition of the existing plant.
To complete the job, utility piping was diverted from the old plant, supported on a set of temporary shoring towers. “It was a bit tricky at times erecting our steel because we were jammed into a corner and the shoring steel towers interfered with our work,” points out Thompson.
To work above the one-storey underground parking garage, Vanbots had to shore M&G’s crane, the “crane paths” and the unloading zone for arriving steel shipments, he says.
The existing mechanical room had to remain fully operational during all aspects of construction.
The roof of the expanded mall’s new steel structure was specified to be the permanent support for the utility piping.
As for the expanded mall, M&G Steel was limited in the size of beams — 24 and 27-inch — it could use in order to maintain the ceiling height requirements. Many of the columns (up to 60 feet in length) had to be boxed-in, plated from flange to flange to increase structural strength while allowing for maximum mall area space, he says.
Erection was further hampered by the tight site that placed restrictions on crane boom height, says Thompson.
Darrell Sakauye, project engineer for structural engineering consultant Banerjee & Associates Ltd., says because the mall required a flexible design to allow for future tenant space renovations, the steel structure incorporated a lot of moment frames, or steel framing with minimal bracing. That resulted in a design requiring large beams and columns for structural strength.
At the same time, some of the beams had to be shallow — 18 inches instead of 24 inches — to maintain the same clearances as the existing mall has, the engineer.
The shallow beams were fabricated with heavier steel to maintain structural strength requirements.
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