Architecture Meets Physics: The Skyscraper and the Pendulum

"728 ton pendulum"
The Long Now Foundation (June 25, 02008)

"In my research of large pendulums for the 10,000 Year Clock I came across the beautifully designed tuned mass damper in the Taipei 101 tower. Basically really tall buildings are themselves massive pendulums, as they are built to sway in the wind and earthquakes. However very tall buildings in earthquake zones need something to dampen this motion...."

Illustrated, with a video.

Pretty good discussion of an important tall-building issue.