Development of technology for effective seismic vibration control by amplifying the physical mass of a small weight

出典：IRIDeSクォータリーVol.5 2013

New Technology from IRIDeS

New seismic isolation control technology

Development of technology for effective seismic vibration control by amplifying the physical mass of a small weight

The idea of a “mass damper” to suppress the vibration of a shaking object by adding a weight has been known from former times. A damper or shock-absorber is a device that absorbs and weakens vibration and impact. It has also been known from former times that it is possible to amplify the apparent weight (mass) of a weight used as a “mass damper” by the principle of leverage, and various types of mechanism have been proposed. Among them, the most suitable for implementing a “mass damper” for a building is currently considered to be a ball screw mechanism. When a nut is rotated on a screw, the nut advances on the screw shaft, and similarly, when a ball screw is pushed on a ball screw, the ball nut rotates at high speed as the screw shaft advances. At this time, a small resistance force in the rotational direction of the weight is amplified into a large resistance force in the axial direction of the screw shaft. That is, the ball screw mechanism acts as leverage.

Technology for Optimum Mitigation Laboratory, Hazard and Risk Evaluation Research Division, The International Research Institute of Disaster Science, is proceeding with development of a “mass damper” that can amplify by a factor of several hundred the apparent weight (mass) of a cylindrical flywheel using a ball screw as a leverage. Through joint development with manufacturing partners that can produce a highly accurate ball screw mechanism, a damper has been successfully developed with an apparent mass of 1250t, while having a compactness of approximately 2m in overall length and approximately 60cm in diameter.

By installing this newly developed device in a seismically isolated building, it is possible to increase the apparent weight of the building by a factor of between 1.5 and 2, and to realize a seismically isolated building that does not shake easily. However, since the building weight does not actuality increase by a factor of 1.5 to 2, loading on the foundation does not increase nor does the seismic force. When the building is subjected to strong ground motions, the apparent weight increases considerably and resistance (inertia) to the shaking becomes large, so that the shaking is suppressed.

Professor Kohju Ikago (Technology for Optimum Mitigation Laboratory, Hazard and Risk Evaluation Research Division)