Study on the Control of Displacement for Base Isolation Systems Utilizing High-Viscous Liquid (Effects of Eccentricity)

Abstract

In Japan, ensuring the structural integrity of cask systems during seismic events is becoming increasingly important. Cask systems, which are free-standing cylindrical structures that contain spent fuel assemblies, are considered as sliding isolation systems. Thus far, analytical studies conducted by the authors have already indicated that cask systems subjected to strong seismic motions, undergo large sliding motions, and in the worst case, may collide with one another. Therefore, reducing the sliding motions of casks to avoid mutual collisions and consequent contamination of radioactive substances is critical. To suppress sliding motions for very heavy free-standing structures such as cask systems, the authors proposed a sliding motion suppression system that uses high-viscous liquid and coaxial circular cylinders. This system is installed at the bottom end of the structure and the annular space is filled with a high-viscous liquid. A previous study showed that high-viscous liquid in annular spaces provides added damping effects of considerable magnitude, and thus allows the sliding motion to be suppressed. In this study, the added damping effects of the annular space liquid are clarified using a fundamental testing device for various liquid viscosities, ratios of diameters for the inner and outer cylinders, and eccentricities of the inner cylinder. Moreover, shaking table tests are conducted to confirm that the added damping effects suppress excessive displacement.