Calculation of Bottom Node Stresses in Oil Tank When Uplift Occurs due to Excessive Internal Pressure

When breather vent attached on the tank roof does not work properly or vent capacities based on normal breathing is inadequate to cope with the increased rate of vaporization of the contained liquid, the internal pressure in the tank increase. As a result of the increase of internal pressure, part of the tank bottom may be raised from the foundation base, that is, uplift at the bottom occurs. The stresses increase and rupture may occure at the bottom-to-shell-joint or bottom node. The method of calculating bottom bending moment presented by J. B. Denham is not suitable for the situation. The paper presents the method for calculating bottom node stresses under the condition that uplift occurs due to excessive internal pressure in the tank. The influences of density, level of the contained liquid, and internal pressure on uplift and bottom node stresses are analyzed.