Watch a giant 728 tonne ball of steel absorb the force of a typhoon

mass damper
Screen capture Taipei 101

I do go on about those ridiculous sliver towers going up in New York City, but have to admit that they are remarkable feats of engineering. Buildings that are tall and slender have to bend with the wind, and they often have what's called a mass damper so that you don't get seasick zillionaires seeing whitecaps in their toilets as they throw up. The structure would still stand without the dampers, but as an engineer noted in the New York Times,

“It’s purely about comfort,” said Silvian Marcus, a director of building structures for WSP, an international engineering consultancy. “It’s related to money and how luxurious the place is.”

They are not a new idea; The Citicorp Center in New York City, built in 1977 and famous for not falling down, had a 400 ton mass damper. The 1,667-foot tall Taipei 101 in Taiwan, the tallest building in the world when it opened in 2004, has a sphere that's 18' in diameter, weighing 728 tons, hanging on straps between the 87th and 92nd floor. I do not know how they got it up there. Last week when Typhoon Soudelor hit, the ball and the building put on a show, a real demonstration of how the technology works.

The inertia of such a big ball means that it doesn't want to move. I know I have that part right. My interpretation was that the ball resists movement and the dampers push against it with giant shock absorbers to reduce the sway of the building. This can be also be done with giant springs; some buildings even have giant tanks and do it with sloshing water. A commenter complained about my explanation with the dreaded 2005 FAIL insult so I found another:

Acting like a giant pendulum, the massive steel ball sways to counteract the building’s movement caused by strong gusts of wind. Eight steel cables form a sling to support the ball, while eight viscous dampers act like shock absorbers when the sphere shifts. The ball can move 5 ft. in any direction and reduce sways by 40 percent.

I am an architect, not a structural engineer, so I probably have it backwards. But everything is relative so the video is showing a bit of the building moving and the ball moving in opposite directions. It's pretty amazing.

111 west 57th© 111 West 57th

But I can't let a great bit of engineering stand in the way of a rant. These tuned mass dampers are very expensive, but they are enablers of some of the most extravagant wastes of resources on the planet, if you divide the amount of steel and glass by the number of inhabitants in these supertall, superslender Pikettyscrapers. It may be Earth Overshoot day for the average planetary citizen today, but the inhabitants of these buildings probably reach Overshoot day on January 3rd.

Oh, but it is terrific and amazing engineering.

Tags: Green Building | New York City

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