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Jalpaiguri Govt. Engg. College

Tuned Mass Damper

By: Subhajit Kumar Biswas Subhajit Ghosh

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CONTENTS

• Introduction• History

• Why to Use TMD• Design Process of TMD• General Principle of TMD• Effect of TMD on Vibrations• Implementations• Advantages and Disadvantages of TMD• Conclusion• References

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INTRODUCTIONA tuned mass damper (TMD) is a device

consisting of a mass, a spring, and a damper that is attached to a structure in order to reduce the dynamic response of the structure. The frequency of the damper is tuned to a particular structural frequency so that when that frequency is excited, the damper will resonate out of phase with the structural motion. Energy is dissipated by the damper inertia force acting on the structure

• A tuned mass damper, is preferably placed where the structure’s deflections are greatest.

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HISTORY

The TMD concept was first applied by Frahm in 1909 (Frahm, 1909) to reduce the rolling motion of ships as well as ship hull vibrations. A theory for the TMD was presented later in the paper by Ormondroyd and Den Hartog (1928),followed by a detailed discussion of optimal tuning and damping parameters in Den Hartog’s book on mechanical vibrations (1940). The initial theory was applicable for an undamped SDOF system.

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WHY USE TMD ?

• To reduce the action of earthquake in seismic areas.• To provide mitigation against wind forces.

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Design Process of TMD• Measure the frequency and magnitude of the undesirable

motion

• Develop model of existing structure and determine the TMD mass and placement of TMD(s) to achieve vibration mitigation requirement

• Perform prototype testing of the TMD to fine-tune the design

• Measure the motion of the TMD(s) on the structure to confirm performance and that the mitigation objective was achieved

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Types of TMDBased on Control Mechanism :

Active Mass Damper Passive Mass Damper

An active control system is one in which an external power source the control actuators are used that apply forces to the structure in a prescribed manner. These forces can be used to dissipate energy from the structure. In an active feedback control system, the signals sent to the control actuators are a function of the response of the system measured with physical sensors

A passive control system does not require an external power source. Passive control devices impart forces that are developed in response to the motion of the structure. Total energy (structure plus passive device) cannot increase, hence inherently stable.

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General Principle of TMD

•The damper consists of a mass M2, of a spring K2 and of a damping C2

• The value of M2 and K2 are chosen so that the moving part of the damper system can be tuned properly to the structure frequency.

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Effect of TMD on Vibrations

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Effect of TMD on Vibrations

decay curve of structure with no damper

decay curve of structure with a damper

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Implementations

Tuned mass dampers are mainly used in the following applications:

• Tall and slender free-standing structures (Skyscrapers, bridges, chimneys, TV towers)

• Tall and slender free-standing structures (Skyscrapers, bridges, chimneys, TV towers)

• Bidges and pedestrian bridges

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TMD for Skyscraper

Largest Tuned Massed Damper (TMD) in the world-730 tons and 5.5 m diameter

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TMD on different structures

IN BRIDGES IN STADIUM

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Other Skyscrapers with TMD’s• Citicrop Centre, New York • John Hancock Tower, Boston • CN Tower, Toronto • Chiba Port Tower, Japan • The worlds largest building in present the BURZ

KHALIFA is equipped with 11 different TMD’S to to control the vibrations.

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Advantages & DisadvantagesAdvantages Disadvantages

They do not depend on an external power source for their operation.

They can respond to small level of excitation.

Their properties can be adjusted in the field.

They can also be introduced in upgrading structure.

They require low maintenance.

They can be cost effective.

A large mass or a large space is needed for their installation.

The effectiveness of a tuned mass damper is constrained by the maximum weight that can be practically placed on top of the structure

Their effectiveness depends on the accuracy of their tuning, but natural frequencies of a structure cannot be predicted with great accuracy.

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CONCLUSIONS

As we conclude it is very much evident that with certain drawbacks, TMDs are very effective tool to protect the structures from various lateral forces ,like wind forces, earthquake effects, and thereby it can save our property and priceless lives.

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REFERENCESStructural dynamics,Mario Paz www.wikipedia.orgwww.engineeringcivil.orgwww.theconstructor.orgwww.GERB.comwww.csaengineering.comwww.civilumd.eduwww.youtube.com etc.

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YOU

THANK