Tuned mass damper

PPT on TMD.it is a ppt on tuned mass damper.

1. Jalpaiguri Govt. Engg . College Tuned Mass Damper By: Subhajit Kumar Biswas Subhajit Ghosh 1

2. 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 2

3. INTRODUCTION A 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. 3

4. 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. 4

5. WHY USE TMD ? To reduce the action of earthquake in seismic areas. To provide mitigation against wind forces. 5

6. TO REDUCE THE ACTION OF EARTHQUAKE IN SEISMIC AREAS 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. As mentioned above, damping devices had been used in the aeronautics and automobile industries long before they were standard in mitigating seismic damage to buildings. In fact, the first specialized damping devices for earthquakes were not developed until late in 1950 6

7. TO PROVIDE MITIGATION AGAINST WIND FORCES Vortex shedding Fatigue of structure When the structure is exposed to wind vortex which are created at regular intervals; if the frequency of the vortex is in phase with one of the Structures natural frequency, the structure would start to vibrate. When the critical wind speed is in lower range of 10-13 m/sec then repeated vibrations caused may induce fatigue to tall structure. 7

8. 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 8

9. Types of TMD Based 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 sensor s 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. 9

10. 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. 10

11. Effect of TMD on Vibrations 11

12. Effect of TMD on Vibrations decay curve of structure with no damper decay curve of structure with a damper 12

13. 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 13

14. TMD for Skyscraper Largest Tuned Massed Damper (TMD) in the world-730 tons and 5.5 m diameter 14

15. TMD on different structures IN BRIDGES IN STADIUM 15

16. 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. 16

17. Advantages & Disadvantages Advantages 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. 17

18. 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. 18