Andrew Smith
Technical Director & Associate
RWDI, New York City

Bujar Morava
Senior Consultant & Principal
RWDI, New York City

Motaz Elfahal
Vice President
WSP, New York City

Jacopo Cardi
Senior Project Engineer
WSP, New York City

The structural design of many slender high-rise towers is governed by the dynamic effects of wind. When the frequency of wind vortices is close to the natural modes of vibration of the tower, resonance occurs. Resonance can result in significant oscillations, potentially causing the building to sway uncomfortably. The options available to reduce motions to acceptable levels for occupants’ comfort are adding stiffness, adding mass, changing the shape and/or adding damping. In some cases, reducing the number of floors or changing the shape, especially near the top, may be an effective option. Alternatively, the structural engineer can augment the structural components by thickening floor slabs, adding shear walls, etc. until the desired reduction in motion is achieved. However, such modifications, which add mass and stiffness to the tower, also result in additional construction cost and they may not be sufficient alone to achieve the desired reduction in building motions.

The remaining option is to supplement the inherent damping of the building’s structural system (i.e. the ability for the building to dissipate wind-imparted energy). This cost-effective option, by itself or in conjunction with structural optimization, has become more common in recent years. A Supplementary Damping System (SDS) can be an effective way to enhance the overall motion comfort of the building in terms of performance and overall cost.