May 28, 2010

SUPREME GROUP

Building Edmonton International Airport’s control tower in steel instead of concrete made sense because it was faster.

FEATURE | Steel

Edmonton’s Air Traffic control tower steel shearwall system proves to be a time saver

DON PROCTER

correspondent

EDMONTON

Air traffic control towers are usually constructed of cast-in-place concrete but a major steel company is making structural engineers and architects think again.

Their best argument is a steel plate shear wall system for the air traffic control tower and office building underway at the Edmonton International Airport (EIA).

The steel system won for a number of reasons, among them that it requires fewer trades on site, says Peter Timler, corporate business development officer and vice-president of engineering of Supreme Group.

The 1,625 tonne steel shearwall system is being done by Supreme Steel Ltd.Timler says the confined space at the EIA and the restrictions on construction schedules favoured steel. Cast-in-place concrete “didn’t make sense” for the fast-track design.

The steel system has proven a time saver, largely because it is an “all-dry construction method,” he adds. “We didn’t have to worry about keeping the core covered and heated during winter and we didn’t have to wait for it to cure.”

The airport tower consists of large cantilevered floors with heavy supporting steel substructures hanging off each core due to the unusually long spans. Using a thin steel plate shearwall system ensures the two elevator/egress cores of the tower meet the design’s “progressive collapse and post-disaster” design standards, he adds.

Supreme Steel is bolting the cores and infill plates together, rather than the conventional method of shop-welding assemblies. Bolting allows the erector/fabricator more flexibility to make assemblies as large or small as required to meet safety standards and speed of erection, Timler says.

Normally, three or four-storey segments are constructed at a time. However, because of the “hot work limitations” (no welding during airplane refuelling) and the possibility of wind interfering with erection of the large segments, it was more practical to configure smaller assemblies for control.

Timler adds the limitations on size and height of cranes permitted at the airport were also factors in the decision to go with smaller assemblies.

“This hadn’t been considered in the original design,” he says. “The engineer was following the conventional method of shearwall cores in buildings.”

The tower also requires about 180 steel cladding frames fabricated on site for the zinc cladding finish and window frames. “It’s a complex geometry,” says Timler, noting 11 mock-up frames are being installed first.

While the airport project might be the first time a steel plate shearwall system has been specified for an air traffic control tower, it probably won’t be the last. Timler was part of a Vancouver team of consultants selected in an RFP by the U.S. federal aviation authority to design post-disaster, blast-resistant air traffic control towers.

“Our team was the only one that came up with steel plate shearwalls.” Such designs have been around for a few decades for use in other building types but their design is complex, admits Timler. “We have looked at this system for office buildings of similar size and it could become a player.”

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