Response of Passively-Controlled Tall Buildings in Tokyo during 2011 Great East Japan Earthquake

Many tall buildings in Tokyo metropolitan area were strongly shaken during the East Japan Earthquake, March 11, 2011. Most of them are less than 40 years old, and have not experienced such strong shaking. This paper discusses some of the tall buildings that have passive control dampers and are instrumented with sensors. The buildings have steel dampers, oil dampers, viscous dampers, or combination of some of these, and showed distinct responses depending on dampers. The building with steel dampers showed high floor accelerations, since dampers remained elastic due to the level of shaking below their yield limit. In contrast, the velocity-dependent dampers such as oil and viscous dampers dissipated seismic energy, and raised the damping ratio. Hundreds of dampers are used for each tall building, but the damping ratio was 3.5 to 5% typically. The moderate damping, however, was effective in reducing responses, compared with the undamped tall building.