How New York City Skyscrapers Withstand Strong Wind

Journalists Edition inosmi.ru They talk about how the skyscrapers of New York can withstand a strong wind, the gusts of which are sometimes very strong.

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Gravitation

The engineers of our time have harnessed gravity: with enough metal and high-strength concrete in the frame, the high-rise will stand. A more recalcitrant enemy is the wind. Gravity pulls down, but wind can come from anywhere. It can push, suck, or do both in turn. Unlike gravity, wind varies depending on the city or season. The wind dynamics are the worst. It changes from everything it touches, and the wind even shapes itself, directing currents to all its neighbors. Gravity is impressive and understandable, but give free rein to the wind - it will gather itself and begin to rebel.

When in 1977 was completed the construction of a city center with a slanting roof, it was not very likely that the building could stand. A skyscraper with a height of 279 meters rests on 4 piles, leaving a decent clearance between the ground and its foundation. Design Engineer William Lemezourie (William LeMessurier) praised for his achievements, but the following year, one student engineer noted that this building (which is now called 601 Lexington) can really crash - with a strong wind. Welders rushed to make emergency fortifications, and during the impending hurricane Ella, the evacuation of this area was discussed. But Ella turned to the sea, and Midtown was safe.

Cut corners

One way to cheat the wind is by cutting corners, which break the suction forces on the sides of the building. Pinnacles and antennas undergo a thorough examination, the level of which is not inferior to the examination of yachts at the America's Cup regatta. In the case of 432 Park Avenue, the design team used 5 layers of skylights, each 2 stories high, where the façade is open, allowing air to pass through and draining its vortices. These horizontal stripes give the high-rise a visual rhythm, but they are there because of the wind.

Dampers

When design tricks run out, engineers can reduce vibrations by installing "inertial dampers" at the top of the building. One version consists of a large mass mounted on a suspension system with pistons that resist the movement of the mass. The damper works like a pendulum, but oscillates with the natural resonant frequency of the building, that is, when the high-rise tilts, this mass pulls it back, instead of synchronizing it, stabilizing it. Hidden at 432 Park Avenue are 2 dampers with a total weight of 1,3 thousand tons. Building Engineer Sylvain Marcus (Silvian marcus), director of building design in the American branch of the company WSP / Parsons Brinckerhoff, visited one of the top floors with a group and asked if anyone felt anything. They told him no. He placed the laser pointer on the floor, pointed it upward, and walked away. The dot moved from side to side as the high-rise tilted.

“They said, ‘This is incredible; We don’t feel anything,” Marcus shared with me. In buildings with high quality dampers, most people will not notice vibrations in normal weather. For ultra-tall residential skyscrapers, inertial dampers are rare blessings of modern luxury civilization that remain invisible.

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