Tuned mass dampers - Definition

Tuned mass dampers are typically huge concrete blocks mounted in skyscrapers and moved in opposition to the resonant frequency of the structure, by means of springs or gravity.

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.

Physics

Tuned mass dampers can stabilize the heights of tall buildings against violent motion. The presence of a tuned mass forces a comparatively lightweight building structure to overcome the inertia of a giant concrete block placed in such a way that the block only begins to move in one direction just as the building begins to move in the other, thus damping the building's oscillation.

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
• London Millennium Bridge

External link

• Structures Incorporating Tuned Mass Dampers (http://nisee.berkeley.edu/prosys/tuned.html)

Example Usage of dampers