# Watch the Incredible Force of a Typhoon Move a Skyscraper's 700-Tonne Mass Damper

Mass dampers are designed to counteract the swaying of a skyscraper as it’s buffeted by strong winds or earthquakes. But it’s incredibly rare to see one of these huge devices moving more an a few inches. Unless, of course, there’s a typhoon nearby.

As the deadly Typhoon Soudelor swept across Taiwan and eastern China last week, winds reached upwards of 130 mph, bending post boxes and lifting 747s off the ground in Taiwan. How did Taipei 101, one of the world’s tallest buildings at 1,651 feet, deal with the force of the winds? Like most supertall skyscrapers, 101 has something called a mass damper that’s designed to counteract the lateral (sideways) force of winds. And during the worst of the storm, it broke a record for how much it swayed, as Popular Mechanics explains.

Starting at the 87th floor and ending at the 92nd, a huge steel sphere hangs suspended in an open chamber inside the building’s core. The logic of putting a 720-tonne steel ball in the upper floors of a tall skyscraper isn’t immediately obvious, but most tall buildings depend on these devices. You see, when a lateral force—like wind or earthquakes—shakes the building at its foundation, the upper floors of the building feel the movement the most, swaying as much as several feet in either direction.

Mostly, that just makes people nervous—and nauseous, as The New York Times recently explained—though stronger forces can certainly become dangerous structurally, too. When those forces push a building in one direction or the other, a sensor detects the movement and the mass damper sways in the opposite direction like a pendulum. The huge weight of the sphere counteracts the forces, and keeps the upper floors in a relatively static position (check out this graphic I made explaining the idea a few years back).

Taipei 101 sits on a fault line, so it’s designed to shake a bit. Back in 2008, the massive Sichuan earthquake rocked the building significantly, with people inside the mass damper chamber capturing amazing footage of the sphere swinging to counteract the tremors. It was hard to imagine the building would ever be put through more than that—until last week. Popular Mechanics’s Eric Limer explains that just before 7AM on August 8th, the intense winds of the typhoon moved the damper more than three feet from its resting spot—setting a record for most extreme movement. Here’s the footage of the event:

It might not look as extreme as a 747 being lifted off the ground, but consider that the amount of movement you’re seeing here is directly related to the amount one of the biggest skyscrapers on Earth was swaying, 1,671 feet above the city. Thank god for structural engineers.

[h/t Popular Mechanics; Reddit]