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One King West, the 51-storey Toronto hotel and condo tower, is nicknamed The Sliver. The trend to slender showpiece towers is growing in Canada and the U.S. as developers shoot for the clouds to maximize small plots.
One King West, the 51-storey Toronto hotel and condo tower, is nicknamed The Sliver. The trend to slender showpiece towers is growing in Canada and the U.S. as developers shoot for the clouds to maximize small plots.

Engineering

Slimmer, taller buildings brave the winds Add to ...

The weather outside is fierce as the winds whip off Lake Ontario.

One King West, the 51-storey hotel and condo tower, rises through the clutch of downtown Toronto skyscapers, like a thin wedge jutting up from the historic Dominion Bank Building, catching the gusts.

The owners boast that the building, which is nicknamed The Sliver, has the narrowest height-to-width ratio for a residential building in the world. At its widest, the building’s ratio of height to width is a slender 13 to 1. But in its narrowest section, which is only 8.5 metres wide, the ratio is approximately 22 to 1.

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From inside looking down to the street, one has to quiet that inner voice wondering whether, like in any high-rise, this super-slender tower is really so impervious to nature, wind and basic physics.

“What is interesting is that the construction industry has grown up on a 35-storey condo or 35-storey office. Normal stops at 35,” said Tibor Kokai, a structural engineer at Read Jones Christoffersen in Toronto. “Now we are beyond normal. Above 35, everything is different.”

A specialist in tall buildings, Mr. Kokai notes that numerous soaring high-rises and office towers with relatively small footprints are being planned for Toronto and other densely packed downtowns. Whereas 35 storeys may have once seemed tall for such buildings, some will follow trends outside Canada and rise more than 60 and 70 storeys.

Midtown Manhattan has seen an array of new, slender showpiece towers, highlighting a trend that most predict will only become more prevalent as developers shoot for the clouds to maximize small plots.

One57, the Christian De Portzamparc-designed handheld shower nozzle of a high-rise still under construction, will tower above nearby buildings south of Central Park. (This was the building left with a crane dangling precariously after Hurricane Sandy swept by in October of 2012.)

Another among the new midtown New York buildings vying for the attention of the megarich and the record books in terms of highest residential tower on the continent is 423 Park Avenue.

Any child playing with Lego knows that connecting one piece on top of another eventually results in the whole thing toppling over. These buildings, however, are like Lego pieces with all sorts of highly engineered tricks inside – they are constantly correcting and adjusting to lateral winds.

At the top of One King West rests a massive weight. Known as a liquid damper, it is hidden, along with the building’s other concessions to stiffness, such as concealed outrigger columns and massive foundation anchors.

The damper, basically high-tech tanks of water, automatically adjusts as a counterweight to decelerate the building’s lateral sway. As buildings reach to the sky on ever-smaller plots, these towers are like finely tuned instruments – taut and tuned to resist winds.

“Honestly if you’re asking an architect or a developer, he would like to have a normal plot. But those are simply not available. Like in One King West, there are two buildings on either side, and nobody could touch them,” said Agha Hasan, practice leader for tall buildings at WSP Canada and the lead structural engineer for the tower, which opened in August of 2005. Embroiled in an intense legal dispute between former development partners Harry Stinson and David Mirvish after it opened, the building is now owned by the condo residents.

The leaning of a building is measured, rather frighteningly, in terms of lateral acceleration. That is, how fast a building is accelerating in a certain direction. The limit allowed is 17.5 milli-g’s. A milli-g is one-thousandth the force of gravity, and so this is only 0.175 per cent of the pull of gravity. Six to eight milli-g’s can be felt, and at 17.5, “you feel it, but you’re not concerned, you can sleep in this. Anything beyond that is a sick building,” said Mr. Kokai of Read Jones Christoffersen.

“If you don’t have enough stiffness to control this acceleration, then you add damping,” he added. “Up to now, we built dumb buildings like the Egyptians built the pyramids.”

Other highly engineered options, beyond mere stiffness, include a kind of internal damper in a shock absorber placed between a building’s concrete walls. These are placed at strategic points to reduce vibration caused by wind and earthquakes, explained Michael Montgomery, principal at Toronto-based Kinetica, which makes these dampers.

“The old World Trade Center in New York City was the first building to ever use any type of damping technology,” he said, noting that damping has since made a comeback with the rise of high, slender towers.

Developers have a huge incentive to go taller and skinnier, Daniel Safarik of the Chicago-based Council on Tall Buildings and Urban Habitat said by e-mail.

“Here the math is very simple. The wealthy have shown a willingness to pay nine figures to get a great view and a commodious penthouse. The less room there is to build tall enough to get that view, the skinnier the towers become,” Mr. Safarik said.

The question, of course, is whether narrow skyscrapers are reaching their limit.

“We used to see buildings that were called slender if they were six or seven times their width in height. Nowadays though, we see buildings 10 or 12 or even 15 times as high as they are wide,” said Peter Irwin, a principal at RWDI in Guelph, Ont., a leading firm in wind-testing building models.

“If you can imagine a building that’s 15 times as high as it is wide, that’s almost like a pole. It becomes susceptible to wind-induced vibration problems.”

He explained that when wind hits a building, it peels off in a very long vortex all the way up the building, and then it will do the same thing on the other side seconds later. Each time the wind peels off it pushes the building, inducing shaking.

By the 1980s and 1990s, as tall, slender buildings began to increasingly be built, “the structural engineers were really struggling to stop the buildings moving so much that people would object to the motion. That was the main problem. It was people feeling the motion, not that the building was going to fall down,” Mr. Irwin said.

Mr. Hasan of WSP Canada noted that much has to do with the foundation. “The limit is the foundation, what it can sustain. It keeps on becoming more expensive, but there’s a structural solution always,” he said.

And with demand still soaring, so will heights, many speculate.

“I don’t think we’re near the technical limits of our capabilities,” argued Mr. Safarik. “A number of our experts have gone on the record saying a building of a mile’s height is possible. The amount of volume that the building would need to occupy, particularly at the base, is so immense however, that it would be hard to justify economically.”

He added: “The only X-factor is whether real estate will continue to be the chosen safety deposit box for extreme wealth … to keep driving prices and buildings upward.”

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