Tuned mass damper
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A tuned mass damper is a device mounted in structures to prevent discomfort, damage or outright structural failure by vibration. Typically, the dampers are huge concrete blocks mounted in skyscrapers or other structures, and moved in opposition to the resonant frequency of the structure by means of springs, fluid or pendulums.
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Sources of vibration and resonance
Unwanted vibration may be caused by environmental forces acting on a structure, such as wind or earthquake, or by a seemingly innocent vibration source causing resonance that may be destructive or unpleasant or simply inconvenient.
Earthquakes
The seismic waves caused by an earthquake will cause tall buildings to sway and oscillate in various ways depending on the frequency and direction of ground motion, as well as the height and construction of the building. When the seismic motion causes harmonic oscillation in the frame of the building, where sections of the building are moving in opposing directions, it can result in structural failure.
Wind
The force of wind against tall, lightweight buildings can cause the top of skyscrapers to move. This motion can be in the form or swaying or twisting, and can cause the upper floors of such buildings to move over a meter. Certain angles of wind and aerodynamic properties of a building can accentuate the movement and cause motion sickness in people.
Mechanical or human sources
Masses of people walking up and down stairs at once or stomping in unison can cause serious problems in large structures like stadiums without dampening measures. Vibration caused by heavy industrial machinery, generators and diesel engines can also pose problems to structural integrity, especially if mounted on a steel structure or floor. Large oceangoing vessels may employ tuned mass dampers to isolate the vessel from her engine vibration.
How they work
Tuned mass dampers stabilize against violent motion caused by harmonic vibration. The presence of a tuned damper forces a comparatively lightweight structure to overcome the inertia of a great mass, such as a giant concrete block, placed in such a way that the mass only begins to move in one direction just as the structure begins to move in the other, thus damping the structure's oscillation. The counterweight may be mounted using massive spring coils and hydraulic dampers, and if the axis of the vibration is fundamentally horizontal or torsional, leaf springs and pendulum-mounted weights are employed. Tuned mass dampers are engineered, or "tuned" to specifically counter harmful frequencies of oscillation or vibration.
Examples of buildings that have dampers
- The Citicorp building in New York City, designed by William LeMessurier and completed in 1977, was one of the first skyscrapers to use a tuned mass damper to reduce swaying.
- The John Hancock Tower in Boston had a tuned mass damper added to it after it was built.
- Taipei 101 skyscraper - world's largest tuned mass damper.
- London Millennium Bridge
- The Trump World Tower in New York
- The Wall Centre in Vancouver employs tuned liquid column dampers, which are a unique form of tuned mass dampers
- The Random House Tower in New York
- Bally’s-Bellagio, Bally’s-Caesar’s & Treasure Island-Venetian Pedestrian Bridges in Las Vegas
- Sakhalin-I - Offshore Drilling Rig
- Bloomberg Tower/731 Lexington in New York
- Dublin Spire in Dublin, Ireland. This narrow slender structure was designed with a tuned mass damper to ensure aerodynamic stability during a wind storm.
External link
- Structures Incorporating Tuned Mass Dampers (http://nisee.berkeley.edu/prosys/tuned.html)
- Motioneering - Experts in Building Motion (http://www.motioneering.ca/Public/Portfolio.aspx)