Eddy current damper
The 128-story Shanghai Tower is the second-tallest skyscraper on earth. The designers wanted a tuned mass damper (TMD) that would not only provide an extra guarantee of occupant comfort on the upper floors, but also serve as a tourist attraction. In addition to hydraulics, the TMD installed here uses an unusual mechanism: eddy current. The bottom of the steel pendulum is fitted with 1800 brick-sized neodymium iron boron magnets. A large sheet of copper sits on the floor over which the pendulum is suspended, and electromagnetic effects create a drag force as the pendulum moves laterally over the copper. The amount of frictionless drag this set-up creates can be adjusted by varying the distance between the magnets and the copper sheet. This innovative TMD delivers a 45% reduction in building acceleration under windy conditions.