Largest tuned mass damper

The largest tuned mass damper is located between the 87th and 92nd floors of Taipei 101, a 508-m (1,667-ft) skyscaper in Taipei, Taiwan, China. The pendulum has a 660-tonne (728 ton) weight and hangs from mountings built into the 92nd floor of the building. It was designed by Motioneering and constructed by A+H Custom (both CAN). Taipei 101 was completed on 31 December 2004.

All structures sway or shake to some degree as they are subjected to external forces such as wind, seismic tremors or the shaking of passing traffic. A certain range of movement is allowed for in designs, and that is the safest way for a structure to respond to external pressure. However, engineers are always looking for ways to quickly damp (dissipate or absorb) these vibrations. Undamped movement can settle into a pattern that resonates with the structure itself, causing increasingly extreme movements and potentially disastrous damage.

A tuned mass damper is essentially a heavy weight that is not directly attached to the structure it sits inside. The pendulum or sliding weight is coupled to the structure through shock-absorbing elements (or dampers) – such as springs or hydraulic pistons – that constrain its range of motion.

When the building begins to sway off centre, the uncoupled weight will lag behind, pushing against the dampers on the opposite side to the building's direction of movement. The resistance in these dampers is calibrated so that the weight will reach its maximum extension at the same moment that the building reaches the farthest point of its swing. This means that the weight rebounds as the building does, setting up an oscillation (backward and forward movement) that is in precise opposition to the movement of the building. This counterbalance saps the energy of the building's movement and transfers it to the dampers, which dissipate it as heat.

There are two reasons why Taipei 101's damper is so large. The first is the height of the structure – it was the tallest building in the world from 2004 to 2010 – the second is the environment in which it was built. The island of Taiwan gets regular earthquakes and is frequently battered by typhoons (tropical cyclones). The building needed to be able to withstand the rare extreme events and maintain the comfort of its occupants as much as possible (buildings with a pronounced tendency to sway, such as the Willis Tower in Chicago, tend to make people feel seasick).

Taipei 101's mass damper has a maximum extension of 1.5 m (4 ft 11 in), but it has never actually been required to move this far. The farthest it has swung is 1 m (3 ft 3 in), which occurred in August 2015 during Typhoon Soudelor, which battered Taipei with 100-mph (160 km/h) winds.