What is a tuned mass damper?

A tuned mass damper (TMD) is a heavy mass mounted on springs or hung as a pendulum inside a structure, connected to it through dampers and tuned so that it counteracts the structure’s vibration. It is used in tall, slender buildings, towers, chimneys and lightweight bridges that start to sway under wind, footfall or traffic.

How it works

Every structure has a natural frequency: the rate at which it swings back and forth by itself once set in motion. If a load such as wind vortices or the rhythm of walking people matches that frequency, resonance builds up and the movement becomes large.

A TMD works in three steps:

1. Tuning: the mass and spring stiffness are chosen so that the damper has almost the same natural frequency as the structure.
2. Counter-movement: when the building moves left, the mass lags behind through inertia and moves right relative to it, pulling the structure back.
3. Energy absorption: the dampers turn kinetic energy into heat so the vibration dies out faster.

The mass is usually only a small percentage of the building’s mass. A TMD does not make a structure stronger; it reduces movement and so improves comfort.

Examples

• Taipei 101 (Taiwan): a steel sphere of about 660 tonnes hangs as a pendulum near the top. Guinness World Records lists it as the largest tuned mass damper in the world.
• Millennium Bridge (London): the footbridge swayed sideways so much after opening in 2000 that it was closed. After additional dampers, including tuned mass dampers, were fitted, it reopened in 2002.

Application

• Skyscrapers and slender residential towers, against wind-induced sway.
• Footbridges and lightweight staircases.
• Chimneys, masts and wind turbines.
• Floors in buildings with machinery or sports halls.

Practical tips

• Measure first: have a vibration survey carried out before choosing a solution. A TMD only works well at the frequency it is tuned to.
• Specialist design: tuning, damping and suspension need a dynamic analysis by a structural engineer.
• Recheck after alterations: if the mass or stiffness of the structure changes, the damper may go out of tune.

Related terms

• Construction vibration
• Vibration survey
• Earthquake resistant
• Suspension bridge
• Structural engineer

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