A pendulum in a skyscraper

Why tall buildings need help

A very tall, slender building sways in strong wind, and people on the upper floors can feel it. Swaying that is safe for the structure can still be unpleasant for the people inside.

A tuned mass damper is a large mass, hung or mounted high in the building and tuned to swing at the building’s own rhythm. It is not rigidly fixed to the structure but connected to it through shock absorbers. When the tower sways one way, the mass lags behind and pulls the other way, and the shock absorbers turn the energy of the motion into heat.

A building’s own rhythm

Every building has a natural rhythm at which it prefers to sway, a little like a child on a swing. Researchers from Academia Sinica’s Institute of Earth Sciences, using seismometers installed in the tower’s fifth basement level and on the 74th and 90th floors, found that Taipei 101’s fundamental mode is near 0.15 hertz: one full sway takes roughly six to seven seconds.

That is the rhythm the damper is tuned to. Pushes that arrive at about that rhythm, from wind or from distant earthquakes, are the ones that can build up motion in the tower, so a mass that swings at the same rhythm, but out of step, can take the energy out of it.

A tower designed for wind

Taipei 101 is a 508-metre, 101-storey tower, completed in 2004, with a five-storey basement and a six-storey retail building around its base. The engineering firm Thornton Tomasetti, which provided the structural design concept and preliminary designs to C.Y. Lee Architects, describes a braced-frame core with multiple outriggers, and a tower built from eight repeating modules of eight storeys each, narrower at the bottom and wider at the top.

It also says the building’s exterior form was refined with the architect and a wind engineer to reduce wind forces, because Taipei lies in a typhoon-prone area. For earthquakes, the design uses perimeter moment frames and special connections in the core.

One damper, three numbers

Sources give different figures for the damper’s mass. Guinness World Records lists the largest tuned mass damper as the one in Taipei 101, at 660 tonnes. Thornton Tomasetti speaks of a 730-ton damper hanging from the 92nd floor. Motioneering, the company that designed, built and installed the dampers, lists a 600-tonne pendulum damper plus two 4.5-tonne dampers in the spire.

Part of the difference may be the unit: 730 US short tons is about 662 metric tonnes. The figure of 660 metric tonnes is also used by Taipei’s official travel platform and by the Academia Sinica researchers who studied the tower. Because the sources do not agree exactly, this guide does not pick a single figure.

Sources also differ slightly on where it sits: Guinness places it between the 87th and 92nd floors, hung from mountings on the 92nd, while the Academia Sinica paper places the ball between the 87th and 91st floors.

How it is built

Taipei’s official travel platform describes the damper as a sphere 5.5 metres in diameter, made of 41 layers of steel plate, each 12.5 centimetres thick, hanging from the 92nd floor down to the 87th. According to Guinness World Records, it was designed by Motioneering and built by A+H Custom, both Canadian firms, and it can move up to 1.5 metres.

Its largest recorded swing, 1 metre, came during Typhoon Soudelor in August 2015, when Taipei saw winds of about 160 kilometres per hour.

Wind and earthquakes

Taipei 101 calls it a wind damper, and comfort in strong winds is its main job. Thornton Tomasetti says it reduces building movement caused by strong winds and earthquakes and makes the building more comfortable for the people inside.

Measurements show how this works in practice. The Academia Sinica team reports that the damper swayed during Typhoon Longwang in 2005, the Wenchuan earthquake in China in 2008 and Typhoon Fanapi in 2010, but not during the great Tohoku-Oki earthquake off Japan in 2011, about 2,500 kilometres away. Most of the energy of that shaking under the building lay at slower rhythms than the tower’s own, so the tower was not strongly excited. A computer study published in the Journal of Applied Science and Engineering, checked against wind tunnel tests and field measurements, reached a similar picture: the damper is very effective against wind-induced vibration and less effective against distant earthquakes.

How Taiwan measures those earthquakes and typhoons is explained on Watching the ground move and Reading a typhoon warning.

Seeing it

Visitors to the 89th-floor observation deck can see the damper. Tickets and opening hours are on the Taipei 101 website, and an outdoor platform on the 91st floor opens depending on the weather (status as of 3 November 2026). More places to visit are on Science Travel.