During the 2003 Tokachi-oki, Japan earthquake, many oil tanks located in Tomakomai were damaged by sloshing due to the long-period strong ground motion. It is especially noted that the single-deck floating-roofs of seven tanks collapsed as they sank with the buckling failure of the pontoons, which resulted in fire accidents of two tanks. To clarify the cause of such damages, it is necessary to investigate in detail the sloshing behaviors in consideration of the existence of a floating-roof. However, so far most of the researches on sloshing have treated only the case of a free surface or the case of a rigid floating-roof, and have not considered the case of an elastic floating-roof, which is used in an actual tank. In this paper, the authors discuss the problem on the basis of fluid-elastic vibration analysis, that is, they investigate the sloshing behaviors of actual floating-roof models with single-deck type and double-deck type and indicate several important viewpoints on the seismic design which has hardly been taken into account hitherto.

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