A tuned-mass damper (TMD) is a specially-designed structural/mechanical element that can be incorporated into a new structure during the construction phase or added to an existing structure to reduce the vibration of the structure. TMDs are most effective where the structure's motion is caused by one or more resonant modes of the structure. The TMD (or multiple TMDs) extracts vibration energy from the structural mode it is "tuned" to. The end result: the structure feels much more stiff than it actually is. Tuned mass dampers often provide a much more economical means for reducing vibration than, say, increasing the stiffness of the structure.
Designing tuned-mass dampers is a multi-step process:
We work with local fabricators and machine shops, such as Johnston Products of Dallas and Halsey Manufacturing, to covert our TMD designs into physical parts.
A similar process is followed when designing TMDs for much larger bridges and buildings. The physics is identical in all cases.
Tuned-mass dampers can be designed to satisfy virtually any criteria. In many cases, the architect will prefer to have the TMDs concealed within the architectural envelope of the structure. The image sequence below illustrates how TMDs can be attached to the primary structure, but hidden within the architectural finish of a flexible walkway. No one will know the TMDs are there. Without the TMDs, this walkway would be highly susceptible to walking-induced vibration that could be disorientating. The TMDs silently "absorb" the vibration making the walkway feel more stiff than it actually is...the TMDs make this walkway functional.
View 1: Walkways are susceptible to walking-induced vibration
View 2: But we want to retain its elegant form
View 3: Solution: Add tuned mass dampers to control the vibration
View 4: The TMDs must be attached to the structural frame
View 5: and are most effective near midspan
View 6: and at the edges of the walkway
View 7: Steel plates provide the required mass and stiffness
View 8: Two TMD designs may be required to control multiple modes
View 9: The initial design is based in structural dynamics analyses
View 10: Fine tune the TMD design using test data…
View 11: obtained during construction when the walkway is nearing completion
View 12: Final adjustments are performed during TMD installation
View 13: The TMDs cannot be seen nor heard
View 14: but the walkway feels much more stiff
Different Types of Shock and Vibration Mitigation Systems
Contact Dr. James Lamb at 214.412.8388 or via email at email@example.com
Tuned mass dampers will reduce the vibration relative to the pre-installation levels. An example of the original vibration level and the vibration level measured following installation of the TMDs is shown in the figure. Two commonly-used reference levels are shown in the plots. The "Perception" level corresponds to the ISO-defined root-mean-square (RMS) vibration level where most people become aware of vibration. The "Office" level is commonly used as the maximum-desired vibration level for office environments and is defined to be 4 times higher than the Perception level. The Perception level is often used as the maximum-permissible vibration level for hospital operating and patient rooms.
In the example shown here, the original vibration levels significantly exceeded the desired maximum vibration level for an office environment. We performed a site vibration survey to measure the vibration and to determine the resonance frequencies of the floor system and designed four tuned mass dampers to address the 5.8-Hz floor vibration mode and to be placed on the floor slab (under a raised floor system). The vibration levels were measured once again following installation of the TMDs. The vibration levels near the TMD design frequency are 70% lower than the original levels - a very successful result.