Aerodynamics and Vibration Control
In the last half-century we have witnessed an unprecedented boom in the construction of tall buildings and special structures, in aspects related to their architectural complexity, freedom of expression and structural sophistication. This is without doubt due to the remarkable revolution in our improved state-of-the-art design tools. More accurate and realistic numerical methods today allow for a greater certainty than ever before, the means to predict how a given structure would behave in extreme loading conditions. Advanced methods for aerodynamic and dynamic optimization permit us to attain shapes, heights and slenderness that were until recently taboo. We have become less conservative in our design assumptions, and when the traditional possibilities for vibration reduction are exhausted we may turn to Tuned Mass Dampers (TMD s), Tuned Liquid Column Dampers (TLCD s), and other novel mechanical devices to help us defy old limitations. This paper presents several examples of such vibration solutions developed at Motioneering Inc., with insight made possible by the use of wind tunnel testing at RWDI.
North America’s Largest TLCD The first example involves the 308 m tall Comcast Center (also know as One Pennsylvania Plaza), which currently is under construction in Philadelphia, PA. It will have one of the largest TLCDs in the world, and quite possibly be the largest in North America when it is complete. Because of the slender building footprint, damping was only needed in one direction, instead of the more typical configuration of two perpendicular tanks. Initially the predicted accelerations were considerably higher than the recommended comfort limits.
To address this, a very high mass ratio was required for motion control. The TLCD moving mass would consist of over 1,200,000 liters of water. The tank would be almost as wide as long which is an unusual configuration. Due to its expanded width, the tank was divided lengthwise in two to avoid water flow off-axis. The Comcast Center’s TLCD will be located above the mechanical floor at the top of the building, at a height of 280 m. Other TLCDs designed by Motioneering include Random House Building, New York, NY (644 tonnes), and Wall Financial Centre, Vancouver, BC (417 tonnes).
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Tex by Trevor Haskett, Scott Gamble and Stoyan Stoyanoff, Motioneering Inc., RWDI, Canada