DESIGN CRITERIA AND LOADS
Peter A. Irwin and Brian Breukelman
A traditional solution to the problem of excessive motion of tall buildings under wind action is to add more structure so as to stiffen the building and increase the mass. However, another approach is to supplement the damping of the structure. Some of the first buildings where this approach was taken were in North America. An early example is the World Trade Center towers, New York, which were designed in the 1960's with viscoelastic dampers distributed at many locations in the structural system. In the 1970's the Citicorp building in New York, which has a single Tuned Mass Damper, weighing 400 tons, at the top was constructed. The Columbia Seafirst Center in Seattle, with distributed viscoelastic dampers, followed in 1984. There have been a few other applications (e.g. John Hancock tower, Boston, as a retro-fit, 28 State Street, Boston also as a retro-fit) but not many. Bearing in mind the large number of tall buildings constructed since 1960, there have thus been relatively few in North America, compared with Japan say, where the concept of adding damping has been applied for reducing wind response. However, as we view the scene in the year 2000, there does appear to be a renewed surge in activity. At the time of writing there are now at least six tall buildings under construction with dampers incorporated as part of the design to resist wind excitation. These buildings are in Chicago, New York, San Francisco, Boston and Vancouver. The author's firm RWDI became involved with these projects initially through wind tunnel testing models of each building and, in several cases, was assigned the task of designing the damping systems.