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 oscillations of the structure by means of springs, fluid or pendulums. High-tension lines often have small barbell-shaped Stockbridge dampers hanging from the wires. See also damping.

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 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

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