Senior Project Engineer
GERB Vibration Control Systems, Inc, Denver
Vibration in urban settings comes in many forms. Perhaps the most commonly discussed at CTBUH is low-frequency vibration (less than about 0.25 Hertz) due to wind-induced vibration in tall buildings. The magnitude of such low frequency vibration is predicted by wind engineers as accelerations in terms of “milli-g” or as the dynamic component of overturning moments, or shear loads. Should these vibrations be predicted to cause occupant discomfort, large tuned masses (tuned mass dampers, tuned liquid mass dampers, and others) may be installed near the top of the building to effectively increase damping and reduce vibration magnitude.
While these low frequency vibrations, and particularly the means for controlling them, may be the “celebrities,” there are numerous other types of vibration, and associated means of mitigation, in the urban setting. Examples of these “supporting actors” include: footfall-induced (or, more generally, human activity-induced) vibration, vehicular and railway-induced vibration, and seismic-induced vibration. Control of these other types of vibration can improve human comfort but may also be crucial for the successful operation of sensitive equipment (e.g. MRI machines, microscopes and lithographs) or for human safety.
Tall, slender structures with tuned masses are discussed in detail, as this typology is most often at the center of building vibration discourse. However other typologies that are less-emphasized also receive focus, and may subsequently encompass more widespread types of vibration within the urban setting. Vibration criteria associated with these forms of vibration are covered, and examples of vibration mitigation schemes are also provided.