For manufacturing equipment of VLSI chips, etc., it is desirable to have isolation floors which are effective not only for strong earthquakes, but also for weak earthquakes and even ambient micro-vibration. A three-dimensional isolation floor was developed to satisfy such requirements. For horizontal isolation, each column of the floor was supported by a newly developed multi-stage rubber bearing which provided the floor with a horizontal stiffness corresponding to a natural frequency of 0.4∼0.5 Hz, and could undergo a horizontal displacement of 20 cm. For vertical isolation, the floor was equipped with inner frames suspended from beams of the floor by coil springs, on wich the equipment was mounted. The inner frames, loaded with the equipment, had a vertical natural frequency of 0.9 Hz. Seismic excitation tests and micro-vibration tests were carried out for a large-scale model of the floor having dimensions of 4×4×1.8
Hm and a weight of 9 550 kg. The tests showed that the floor performed very satisfactorily for various vibrations whose amplitudes ranged from 10
-3 to 10
0 m/s
2 in acceleration, and from 10
-7 to l0
-1 m in displacement.
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