Abstract
The current seismic design codes of aboveground oil storage tanks (ASTs) are conducted based on the beam-type vibration with circumferential wave number m=1. The oval-type vibration with m≧2 in which shell plate vibrates in a petal shape due to local mass and stiffness, initial imperfection or nonlinear vibration occurs in ASTs. The initial stress due to hydrostatic pressure was reported to increase the natural frequency in high m range by several studies. The circumferential tensile stress on shell plates caused by hydrostatic pressure increases the stiffness and as a result the natural frequency is also increased. Wind girders are installed to the shell plates in ASTs for the prevention of buckling by wind pressure. The wind girder which is a ring stiffener increases the stiffness of the shell plate. In this paper, the natural frequency of the oval-type vibration in a large sized AST is analyzed and the effect of the wind girder on natural frequency is studied. The method is the free vibration analysis by axisymmetric finite element method considering coupled vibration of internal liquid and tank.
