Stability of elevated liquid-filled conical tanks under seismic loading, Part II—applications

Abstract

In this paper, the numerical model developed in the previous paper is used to study the seismic performance of elevated liquid-filled steel conical tanks. A number of conical tanks which are classified as tall or broad tanks according to the ratio of the tank radius to its height are considered. The consistent shell element is used to model the tank surfaces, while the coupled boundary-shell element formulation is employed to obtain the fluid added-mass which simulates the dynamic pressure resulting from a seismic motion. Linear springs are used to model the supporting towers. The natural frequencies of the liquid-filled tanks due to both horizontal and vertical excitations are evaluated. This is followed by a non-linear dynamic analysis, using an appropriately scaled real input ground motion, and which includes the effect of both geometric and material non-linearities. Thin-walled structures of this kind may exhibit inelastic behaviour and a tendency to develop localized buckles, thus diminishing stiffness. The consequence could lead to overall instability of the structure. In general, time-history analyses indicate that liquid-filled conical tanks, often possessing apparently adequate safety factors under hydrostatic loading, are shown to be very sensitive to seismic loading when ground motion frequencies contain those of the fundamental frequencies of the vessels themselves. © 1997 John Wiley & Sons, Ltd.