A three-dimensional isolation floor for earthquake and ambient micro-vibration using multi-stage rubber bearings (1st report, tests for the performance of the floor by a large-scale experimental model)

For equipment used in manufacturing VLSI chips, for instance, it is desirable to have isolation floors that are effective not only for strong earthquakes but also for weak earthquakes and even for ambient vibrations. 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 to 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 which the equipment was mounted. The inner frames, loaded with equipment, had a vertical natural frequency of 0.9 Hz. Seismic excitation tests and ambient vibration tests were carried out for a large-scale floor model.