23-01-2013, 04:22 PM
TUNED MASS DAMPER
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ABSTRACT:
The safety of a construction depends on many factors like the load bearing capacity of the soil, the properties of the materials used for the construction, the design of the structure and many other things. The design of the building should consider the factors like the loads coming on the structure and the geological behavior of the constructional site. In the high earth quake prone areas, the design of the structure is made to withstand the Seismic Loadings.
To withstand the high magnitude of seismic loadings in many tall buildings and sky scrapers, Tuned Mass Dampers are used.
TUNED MASS DAMPER:
The seismic waves caused by an earthquake will make buildings sway and oscillate in various ways depending on the frequency and direction of ground motion, and the height and construction of the building. Seismic activity can cause excessive oscillations of the building which may lead to structural failure. To enhance the building's seismic performance, a proper building design is performed engaging various seismic vibration control technologies.
A tuned mass damper, also known as a harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. Their application can prevent discomfort, damage, or outright structural failure. A tuned damper reduces the vibration of a system with a comparatively lightweight component so that the worst-case vibrations are less intense. Roughly speaking practical systems are tuned to either move the main mode away from a troubling excitation frequency, or to add damping to a resonance that is difficult or expensive to damp directly.Mass dampers are frequently implemented with a frictional or hydraulic component that turns mechanical kinetic energy into heat, like an automotive shock absorber. An electrical analogue is a LCR circuit.
Mechanical human sources
Masses of people walking up and down stairs at once, or great numbers of people stomping in unison, can cause serious problems in large structures like stadiums if those structures lack damping 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 Ocean going vessels may employ tuned mass dampers to isolate the vessel from its engine vibration.
Tuned mass dampers are used in other fields like:
• As shock absorbers in motor sport vehicles
• On crank shafts in car production
• To reduce peak loads in space crafts
• To reduce high frequency in power transmission lines
Dampers in buildings and related structures
Typically, the dampers are huge concrete blocks or steel bodies mounted in skyscrapers or other structures, and moved in opposition to the resonance frequency oscillations of the structure by means of springs, fluid or pendulums. The technology of using mass dampers has been adopted in several structures like Taipei101 in Taiwan, Millennium Bridge in London, Grand Canyon skywalk in USA etc.