Since thermal baffles of a fast breeder reactor are clamped-free thin cylindrical shells immersed in fluid, buckling caused by fluid pressure is the most likely type of failure to occur during an earthquake. In order to establish a seismic design method for the thermal baffles, buckling pressures of cylindrical shells, with a radius-to-thickness ratio of 250, were investigated both by shaking-table experiments and by static buckling analyses. It was shown that the dynamic buckling pressures can be predicted by static buckling analyses. It was also found that sub-harmonic vibration occurs under a certain sinusoidal wave excitation and causes a sudden increase in response displacement and that this condition of the subharmonic vibration can be predicted by the elastic stability theory. In addition, a seismic deisgn method for thermal baffles was proposed based on these buckling experiments, static buckling analyses, and dynamic stability analyses.
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