Flipside to Recession
April 2008While a probable recession is on the mind of many an American, Canadians are feeling pretty secure (and a bit smug) about their economic lot. There has been no subprime mortgage debacle north of the 49th and, in fact, housing starts and prices continue to soar in many cities. Toronto’s a good example. Moreover, our dollar remains strong on world markets. It was actually worth 13 cents more than the U.S. greenback in December, an all-time high.
Still, only a fool thinks we’re not immune to what happens in the United States—our largest trading partner—if its downward spiral is deep. The manufacturing industry, one of the mainstays of Ontario’s economy, is already feeling the pinch of a higher trading dollar against the greenback. A lengthy U.S. downturn could severely affect it.
Riding high on the crest of the booming oilpatch, Alberta, however, shows few signs of an economic upheaval, so it’s no surprise that its biggest city, Calgary, is one of the hottest tower crane markets in the country. Over the next two years, the most prominent downtown project will be a 58-story, 1.7 million square foot office behemoth.
Called the EnCana Bow Tower, the crescent-shaped building presents unusual design and construction challenges for many trades—including the two cladding contractors. It will feature an exterior diagrid of structural steel webbing and cladding of aluminum and glass. One of the hurdles is how to expose steel on the inside of the building and clad it in an unusual but rational manner. It is a formidable task.
The design team can’t afford any surprises.
"Once the steel is up, the cladding people have to deal with whatever they are left with,” explains David Jefferies, managing project architect of Zeidler Partnership Architects. Zeidler has teamed up with world-renowned architect Foster + Partners of Great Britain.
The tower features a capless aluminum curtainwall framing system, consisting of 5-foot modules in a split frame that snaps together. The framing, which uses an interlocking split box installation with an integrated thermal break and air seal, is set in straight sections to form gentle curves that develop the bow-shape of the building, explains Jefferies. The bow reduces the wind load on the structure and gusts at sidewalk-level. The design is engineered to be 30 percent lighter than conventional office towers.
The "layers of the skin” of the tower are no different than other towers except at the southeast face where large atria collect solar energy. The interior offices feature sun shade control to minimize solar heat gain from the outer atria, which will be at 12, 18 and 24 stories. Here, the diagrid is free-standing and separated from the floor slab over these heights. By comparison, a typical office building’s floor plates extend out to the face of the wall.
One cladding contractor is Sota Glazing Inc. Its project manager, Pino Donato, says devising an anchor system for the structural steel and cladding system to deal with movement on the southwest face was a challenge. Scheduling cladding installation will be tricky, based on when the steel erections contractor can "stiffen up” the tower enough to prevent movement.
Essentially, the structure will be "tied in” at the 24th floor where the floor plate extends to the exterior wall. "At that point they will let all their braces loose” and cladding installation will commence. The curtainwall anchorage is designed to allow for tolerance (movement of about one inch in all directions) in the steel structure, he points out.
It’s only one of many challenges Sota will face over the next couple of years in a busy city where thoughts of recession are the furthest thing from anyone’s mind.
Don Procter is free-lance writer in Ontario, Canada.