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:
Perform a site vibration survey to document the existing vibration levels and to determine the primary floor resonance frequencies.
Develop a structural dynamics model of the floor system and fine-tune the model to match the measured response.
Add TMDs to the dynamics model where the model indicates they will provide maximum benefit. Use the model to determine the total TMD mass required.
Verify the existing structure has adequate excess structural capacity to support the added TMD weight.
Develop the TMD design drawings for fabrication and perform vibration tests on the prototype TMD prior to final production and delivery to the site.
Deliver and install the TMDs at the site and measure the post-installed performance.
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
Vibration Absorption - Reduce vibration at a location of interest (Tuned-Mass Damper Design). Tuned mass dampers are used to suppress lateral vibration and/or vertical vibration
Vibration Isolation - Prevent vibration from propagating from the source. Vibration isolation systems may rely on springs for or pendulum-like supports for low-frequency isolation
Shock Isolation - Reduce vibration caused by high-amplitude transient impacts
Contact Dr. James Lamb at 214.412.8388 or via email at jlamb@age-se.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.
Tuned Mass Damper Design for a Science Research Building [PDF]
Operations Center Floor Vibration Analysis and Tuned Mass Damper Design [PDF]
Low-Rise Office Floor Vibration Survey and Tuned Mass Damper Design [PDF]
Tuned Mass Damper Concept for Vortex-Induced Vibration [PDF]
Observation Wheel Dynamics and Tuned Mass Damper Performance Analysis [PDF]