In Japan, the study on the development of a 3-dimensional base isolation system to be applied to a nuclear power plant, which requires supreme safety against severe earthquakes, has been carried out since 2000. An idea with the concept of a cable reinforced air spring was proposed as the 3-dimensional base isolation device. The dimension of the air spring applying to the actual power plant is 9 meters in the outer-diameter and 3.5 meters in height. The allowable half strokes are respectively 1.5 meters for the horizontal direction and 0.5 meters for the vertical directions. The supporting weight for a single device is 52MN, where the inner air pressure is about 1.2MPa. This device enables to realize three-dimensional base isolation with a single device, whose characteristics is a natural period of over 4 seconds in the horizontal direction and over 3 seconds in the vertical direction. Furthermore, this device does not require precision mechanical parts just common building materials, which are steel, cable wire, polyester fabric and a rubber sheet. Therefore, the construction cost for this device could be reduced effectively. In order to confirm the performance of the proposed device, experimental tests using the three dimensional shaking table were carried out on the proposed cable reinforced 3-dimensional base isolation air spring, whose outer diameter is 2 meters, being 1/4.5 scale of the actual size. The weight of approximately 392kN including a 4-story steel frame was loaded on the test specimen in order to create inner air pressure of 0.157MPa. As a result, the device was confirmed to function smoothly in three dimensions with natural periods of 1.8 seconds in the horizontal direction and 1.4 seconds in the vertical direction, and is considered that the proposed system can be applied to actual power plants.

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