It is invisible to the human eye, but all high-rise buildings sway slightly in the wind. With gusts of wind, the top of a skyscraper can be mixed from its axis by several meters. this is normal. And the higher the skyscraper, the greater the amplitude of its oscillations.
To minimize this swaying, engineers install giant counterweights at the top of buildings called tuned mass dampers (TMD). In most cases, TMD shock absorbers are a giant ball of steel or concrete, weighing up to 300 - 800 tons! The ball is suspended by springs and pistons at the top of the buildings and balances unhindered as the building tilts change. In fact, its task is to maintain the center of mass of the skyscraper.
Example: On a windy day, the top of a skyscraper is only 300 meters high and can swing 10 centimeters in different directions. Sometimes the occupants of such tall buildings even begin to feel sick from these vibrations - they develop seasickness. Therefore, the tuned TMD mass dampers, by minimizing the vibration amplitude, make the movement of the building almost invisible to its residents.
In 2004, the tallest building in the world was the 509-meter-high Taipei 101 Tower in China. A giant ball-shaped counterweight is installed inside this building, the characteristics of which are amazing! Its diameter is 5.5 meters, and its weight is 728 tons. The ball is able to dampen the vibrations of a skyscraper, even if the wind speed is 240 km / h.
In fact, any skyscraper can be viewed as a giant tuning fork. If you hit it hard, for example, by a gust of wind or an earthquake, the building will vibrate at a given frequency. In this case, the TMD counterweight begins to move at the same frequency as the building, but in the opposite direction. This mechanism does not remove vibration at all, but keeps it under control.
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