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A tuned mass damper (TMD) system consists of a vibrating mass that moves out of phase with the motion of the structure that it is attached or suspended to. As it moves out of phase, the inertial force of the TMD system dissipates the energy and reduces the vibrations placed on the structure. This is accomplished by tuning the TMD to the natural frequency of the structural mode targeted for damping.
TMDs have been successfully added to various structures throughout the world. Structures such as bridges, skyscrapers, staircases, stacks, and antennas can all be excited to high levels of vibration from wind, earthquakes, nearby machines, or traffic. All of these structures require TMD systems to eliminate discomfort, damage, or outright structural failure caused by vibration in the structure. Taylor Devices manufactures viscous damping devices for large scale TMD systems as well as full custom TMD systems for pedestrian bridges, walkways, concert venues, as well as other structures.
Modern pedestrian bridges are sometimes long and slender in form, usually leading to a structural design with relatively low frequency primary modes of vibration. Similarly, some convention centers, hotels, concert halls and/or theaters are built with very long spans. Because of this, the bridge or floor can easily be excited by synchronized activities such as jumping, dancing, or even something as simple as walking. Unlike fluid dampers which convert mechanical energy into thermal energy, a tuned mass damper system will create a forcing function to oppose the induced dynamic structural deflection, thus suppressing motion.
Generally, TMDs are considered effective in applications of controlling structural motion where direct damping cannot be applied. TMDs can be effective in the single frequency that they are tuned to, for controlling motions induced by wind, crowds of people, or other low-level vibration, where damping levels of less than 10% can be used. Multiple TMDs can be used if several modes can be excited by the input causing vibration.
Tuned mass dampers are typically installed in high-rise structures to control a structures response to wind inputs which may cause the building to sway. The amplitude and frequency of sway depends on height, slenderness and rigidity of the structure.
In high-rise buildings, such sway may make people uncomfortable at low frequencies. Some buildings are equipped with dampening devices, like 432 Park Avenue in New York City, to mitigate the swaying effect of the structure and make it a much more comfortable experience for occupants.
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