The Michael Lee-Chin Crystal presents a striking image of interlocking prismatic forms. For the building and design team, completing the Crystal was a taxing job.
The erection of the structural steel was one of the first major challenges for Markham, ON.-based construction manager Vanbots Construction Corp. In a conventional structural-steel building, builders erect part of the steel frame and then start pouring concrete slab floors before adding cladding. The Crystal, however, is anything but conventional. “We had to put up all the structural steel and shore it up before we could pour the concrete and put up any cladding,” John Martin, project director with Vanbots, says.
The structure would have been unstable if a conventional construction approach was taken, he points out.
Unlike most modern steel-frame buildings, the concrete floor slabs at ROM are an integral part of the structural integrity. “In a normal building, you pour the concrete deck and the load is transferred into the beams and then into the columns of the structure to give it support,” Martin explains.
At the ROM, each concrete slab acts as a diaphragm which holds the diamond segments that comprise the overall crystal form together. Each level or crystal within the larger crystal contains three to four diaphragms which prevents the building from collapsing.
The “structural” concrete slabs could not transfer loads into the structural steel frame. The concrete had to be supported independently of the steel otherwise the structural steel would be pre-stressed and overloaded.
Consequently, shoring supported all of the concrete slabs in the structure right down to slab at grade. To carry the heavy slab loads of the concrete, the shoring was specially engineered by shoring engineer CSE Structural Forensic & Rehabilitation Services and prime engineering consultant Halsall Associates Ltd. of Toronto. “It was a complicated thing to engineer,” Martin recalls. “There was a lot of shoring and it had to be positioned just right or you could be crushing the deck with the load.”
The shoring stayed in place until all the concrete slabs were poured. “Normally, you would take out shoring halfway through a project, but we couldn’t do that because the building would move, stress the steel up and overload the structural steel members.”
When it came time to remove the shoring, Halsall was consulted to ensure the removal sequence didn’t cause overloading. “The geometry of the building created a lot of structural problems just in the engineering because when the structural engineers analyzed it during the engineering process they analyzed the final structure and what it would look like,” Martin explains. “The actual loads that came on during the building process were far more problematic than the final loads.”
It took the team a year to come up with a workable design for the concrete slab pours, called the “wet concrete study,” including a lot of what-if scenarios and alternative schemes. The team included Halsall, Vanbots, Mississauga, Ont.-based decking supplier Flynn Canada Ltd., structural steel connections design by Hamilton-based Walters Inc., and CSE.
Martin, who says this project was the most challenging of his career, points out that the complex construction process added about six months more to the construction schedule than it would have taken to build a similar-sized building in a conventional design.