Study on Dynamic Buckling Behavior of a Cylindrical Liquid Storage Tanks under Seismic Excitation (2nd Report, Phenomena on Nonlinear Ovaling Vibration at the Upper Wall)

When a thin walled cylindrical liquid storage tank is exposed to a very large seismic base excitation, buckling phenomena such as elephant foot bulge at the bottom portion and nonlinear ovaling vibration at the upper portion may be caused. In the 1st report, elephant foot bulge phenomena and the liquid pressure effect were investigated. In this report, nonlinear ovaling vibration phenomena were investigated based on the dynamic buckling tests and the external pressure buckling analysis by FEM, using scale models of thin cylindrical liquid storage tanks for the nuclear power plants. The mechanism and the effects of vertical excitation and liquid sloshing were studied and discussed. As a result, it was found that the negative pressure will dominate the occurrence of the nonlinear ovaling vibration and the effects of sloshing and vertical excitation are relatively small. Moreover it was thought that the nonlinear ovaling vibration observed here is buckling phenomeon due to the external liquid pressure.