In nuclear power stations, the storage of a lot of spent fuels is becoming a serious problem because of the shortage of the residual space of the spent fuel pool. It is planned to construct an another plant where the spent fuels are temporarily stored. In that plant, the spent fuels will be installed in a container called canister. The canister, in turn, will be stored in an outer cylindrical container called cask, which will be a free-standing structure. Thus, the cask-canister system is seen as a two-degree-of-freedom coupled system. Therefore, it is very important to evaluate the sliding motion of the cask-canister system subjected to seismic excitations. In an analytical model, the canister and the cask are treated as rigid bodies that are connected by a spring and a dashpot, and liquid is encapsulated in an annular region between the cask and the canister. The equations of motion are derived for the sliding motion when the floor is subjected to a horizontal base excitation. The sliding displacement of the cask and the relative displacement of the canister against the cask are evaluated by numerical simulations. The effects of the liquid in the annular region is effective in reducing the sliding motion of the cask.

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There has been steady progress in research and development of earthquake early warning systems and its application to structural control. In this paper our proposed methodology about forecasting frequency contents of strong motion is first introduced, then its application to feed forward structural control with the usage of semi active control devices is simulated, and lastly it is showed that non-resonance structural control can be achieved before the strong motion of an upcoming earthquake reaches to a building of interest.

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A simplified method for evaluating liquefaction potential under ocean trench type long period earthquakes. Since there is no experience on damage or liquefaction under this type of earthquake, effective stress analyses are made on more than 200 sites that are used in the past investigation on liquefaction damage. Accuracy or effectiveness of existing simplified methods is investigated, and is found that they are applicable to near field earthquake, but they result in dangerous evaluation under ocean trench type earthquakes such as artificial earthquake for coming Tonankai earthquake and recorded accelerogram during the Tokachi-oki earthquake of 2003. The reason is found to be effective number of loading cycles; it is about 10 times larger than that considered in the existing simplified procedure. Then a correction factor for liquefaction strength is proposed in order to evaluate liquefaction potential under this type of earthquakes. The factor is a half of the factor in the existing method; liquefaction strength is to be half of the conventional value when comparing maximum shear stress to evaluate FL value. This method works so that dangerous ratio (ratio of number of layers where onset of liquefaction is identified under effective stress analysis but is not identified under existing simplified procedure to the total number of layers) becomes small to be the same order under near field earthquake.

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