Vibration Control of a Concrete Cantilever Pier Using Tuned Mass Dampers

structure magazine's August 2018 cover

The feature article of the August 2018 issue of the Structure Magazine titled “Reclaiming the Waterfront” is about the City of Vancouver, Washington’s new development along the Columbia River with the Grant Street Pier as its centerpiece. The focal point for this development is a concrete cantilever pier with an iconic and attractive form. The pier’s triangular, post-tensioned concrete deck overhangs the water by 90 feet and provides an expansive view of the river. A cable system and 80-foot-tall mast support the deck.

DEICON designed and fabricated two 11,000 lb tuned damping systems for the pier. There were installed in cavities within the concrete deck, close to the tip of the pier. The units were tuned to the natural frequency of the first mode (flapping mode) of vibration of the pier, measured by DEICON when the construction was nearly complete.

Comparison of the vibration measurements conducted ‘before’ (the installation) and ‘after’ (the installation) of tuned damping systems revealed that the tuned mass dampers abated the vibration of the pier, significantly. More

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Vibration Control of Long Span Balcony Using a Tuned Mass Damper

The balcony inside an up-scale large custom-built, single-family residence, overlooking the large open area of floor below had an unacceptable vibratory attribute. The balcony is supported by a long, wide flange (W21) steel beam that supports approximately 600 square feet of tributary floor area.

tuned mass damper installed inside the beam As anticipated and evident from the measured data, the worst-case vibrations occurred at around 4.2 Hz (the first natural frequency of the long steel beam supporting the balcony edge). Moreover, the modal damping ratio of the structure corresponding the first mode of the structure was predicted to be around 1%.

DEICON designed and fabricated a narrow tuned mass damper systems for the balcony. The TMD was sized to have the nominal active mass of 450 Kg. The depth and height of the TMD were chosen so that it can fit within the W21x182 beam spanning the entire length of the balcony. The remaining parameters of the TMD namely the tuning frequency and damping ratio were selected based on the dynamic attributes of the balcony.

Comparison of the measured balcony vibration without and with the TMD pointed to an excess of 8 fold increase in the damping of the first (target) mode of the structure, from 1.1% (without the TMD) to 9% (with the TMD). Such an increase in damping lowered the walking induced vibration along the open edge of the balcony by the same factor. More

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Monumental Staircase Vibration Abatement Using a Tuned Mass Damper

tuned mass damper installed underneath the landing

Monumental, aesthetically pleasing staircases are getting incorporated more and more in the architectural design of institutional and commercial buildings. Monumental staircases frequently cause vibration serviceability issues. This is due to their complex shapes, and long spans, slenderness, and lack of columns. Such staircases vibrates when people climb up and/or down the stairs. Moreover, the transmission of that vibration to other parts of the building, can cause discomfort to the occupants.

DEICON measured the staircase’s fundamental frequency (6.1 Hz) and damping ratio (2%). Subsequently, DEICON designed and fabricated a 500 lb tuned mass damper targeting the first mode of vibration. The dimensions of the TMD were selected such that it could fit in the cavity underneath the landing, and be out of sight.

Subjective evaluations as well as comparison of the measured staircase vibration without and with the TMD pointed to the effectiveness of the tuned mass damper in dampening its target mode, increasing it from 2% to 10%, abating the vibration of the staircase. More

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Vibration Control of a Pharmaceutical Laboratory Floor System Using Stiffening and Tuned Damping

Based on extensive numerical modeling and measurements the acoustics consultant of the project recommended the stiffening of the frames along with tuned damping of 5 bays of the floor system of a Pharmaceutical laboratory. The floor vibration criterion used was VC-A (50 μm/s RMS in one-third octave bands). The VC criteria take the form of a set of one-third octave band velocity spectra labeled vibration criterion curves VC-A through VC-G, currently published in an IEST (Institute of Environmental Sciences and Technology) Recommended Practice.

tuned mass dampers installed under one of the bays Following the applications of supplemental stiffening steel to the existing beams and girders of the target bays, the natural frequencies of the bays were measured and used in tuning 10 tuned mass dampers targeting the first modes of the 5 bays. The TMDs were installed underneath the 5 bays (2 TMDs/bay) by the steel contractor of the project and commissioned/fine-tuned by DEICON.

Following the commissioning, the acoustic consultant conducted the final measurement of the floor system. The measurement revealed that the vibration amplitudes in the bays where the TMDs were installed were reduced significantly from the untreated floor. The bays with TMDs installed all meet the VC-A criterion (50 μm/s RMS) due to typical walkers in the lab area. More

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Multi-mode vibration Control of a Floor System Using Tuned Mass Dampers

The floor system of a large room at the 3rd floor administration building of a large university with the square footage of around 1760 ft^2s consists of 3 bays exhibited excessive walking-induced floor vibration. This composite floor system is made up of 3 ½” regular weight concrete on 1 1/2” metal deck, supported by 9 wide flange beams.

three modes of the floor system Numerical analysis as well as vibration measurement revealed that the floor system vibrates at 3 different frequencies, corresponding to the natural frequencies of the first 3 modes of the structure, depending on where and at what pace the floor is walked on (perturbed). In modes 1 and 2 the three bays vibrate collectively, but in mode 3, each bay vibrates individually, although at the same frequency.

Reactive damping, provided by appending tuned mass dampers (TMDs) to the floor system, was decided on and implemented for abating the vibration. Six tuned mass dampers (TMDs) targeting 3 modes of vibration were designed, fabricated, and installed underneath the floor system. The couple most effectively with the floor system, the TMDs were installed at the locations where their target modes have the highest vibration level.

Following the installation of the TMDs, floor vibration at the target bays, without and with the tuned mass dampers operational, were measured. Comparison of the two sets of measurements, pointed to the effectiveness of the tuned mass dampers in adding substantial amount of damping to their three target modes, quieting the vibration of the floor system. More

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