Development of three-dimensional seismic isolation system using negative stiffness link mechanism and air levitation mechanism in series (Overview of prototype experimental device and report on full-scale 3-D seismic excitation experiment by E-Defense shaking table)

Abstract

Vibration tests of the prototype of the newly developed three-dimensional seismic isolation mechanism were carried out using several real-scale three-dimensional seismic waves with the world's largest E-defense shaking table. The developed 3-D seismic isolation mechanism has an air levitation mechanism that isolates horizontal vibration and a spring link mechanism that isolates vertical vibration, in series. The air levitation mechanism floats only 50 μm from the floor and is in contact with the floor with a slight air viscous force of a friction coefficient of 1/1000. Since there is no spring force in the horizontal direction in this mechanism, there is no periodic motion and there is no amplification of vibration. Also, since the floating height is very small, the vertical rigidity is very high even in the air, and the rocking motion is not performed. The spring link mechanism combines a negative stiffness link and a positive stiffness link to minimize the spring stiffness. While maintaining the horizontal attitude by the link, a vertical natural frequency of 0.25 Hz was realized. The prototype showed unprecedented high performance of about 20 dB of anti-vibration capability at 1 Hz both in the horizontal and vertical directions, and the effectiveness was verified in this experiment. The seismic waves used for the experiment are the Takatori seismic wave of the Great Hanshin-Awaji Earthquake of 1995 and the Sendai seismic wave of the Great East Japan Earthquake of 2011.

Keywords

• earthquake
• three dimensional seismic isolation
• air levitation
• negative stiffness