Preuplift Method to “Anchor” Liquid Storage Tanks

Abstract

Steel tanks for liquid storage often consist of a cylindrical shell attached to a steel bottom plate which rests on the ground. In many cases neither the bottom plate nor the cylindrical shell are fixed to the ground. When such an unanchored tank is subjected to seismic ground shaking, the lateral inertia of the contained liquid contributes to the overturning moment, but its weight cannot contribute to the stabilizing moment until some uplift of the bottom plate occurs. The hold‐down force, due to the weight of liquid resting on the uplifted portion of the bottom plate, provides the necessary resistance against overturning. However, this benefit of uplift comes at the cost of very high vertical compressive stresses in the tank wall at the base in the region diametrically opposite to where the maximum uplift occurs. The benefits of uplift can be reaped without some of its detrimental effects if the tank wall is preuplifted all around the circumference by means of a ring filler. An annular portion of the base plate is also preuplifted, but is not supported by the ring filler. The weight of liquid resting on that preuplifted portion of the base plate then becomes effective in resisting the overturning moment. For a 127 mm diameter Mylar tank, it is shown by experiment and analysis that preuplift increases the lateral load capacity by a factor of up to 2.