A vibration control device to dramatically reduce shaking caused by long-period earthquake ground motion - a phenomenon in which major earthquakes shake skyscrapers slowly but severely - was shown to the media on Monday after being installed in a 55-story building in central Tokyo.
The new system was installed on the rooftop of the Shinjuku Mitsui Building in Shinjuku Ward, Tokyo, by Mitsui Fudosan Co. and Kashima Corp, the joint developers of the device said to mitigate shaking by about 60 per cent.
The device comprises six pendulum weights of 300 tons each suspended on cables, which sway in the opposite direction from the sway of the building, thus reducing shaking.
The companies said it is the nation's first rooftop vibration control device against earthquakes. Construction costs were about ¥5 billion (S$54.3 m), they said. The building was completed in 1974.
It is said to have swayed up to about two meters for about two minutes during the Great East Japan Earthquake in March 2011.
The device can reduce the sway to 80 centimeters and cut the time of shaking to one-sixth what was already experienced should a seismic event comparable to the 2011 earthquake occur, according to the companies.
When long-period earthquake ground motion occurs, people in tall, swaying buildings are at special risk as the office furniture can injure them as it moves around. Skyscrapers built in 2000 or later have vibration control systems inside while few buildings built earlier have such systems, according to Mitsui Fudosan.