Abstract
Vertical cylindrical tanks for bulk storage of oil and liquefied gas are sometimes constructed on soils that are susceptible to settlement. The types of foundation settlement and their structural effects on the tank are reviewed. An arbitrary operational limit of 1 in 200 is sometimes quoted for the foundation tilt of atmospheric storage tanks. This limit is based on aesthetic considerations and on the effects on pipework connections and other attachments. Many tanks reach this limit before the end of their design life, and tank owners face difficulties in assessing the effects of foundation tilt since the current design and inspection codes give no guidance.
The purpose of this paper is to present a simple method for calculating the overturning moment, shear force and associated stresses caused by tilt of a tank, and to present a rational design basis. The procedures can be used in the design of new tanks to withstand a specified magnitude of foundation tilt and also to predict the maximum allowable tilt for existing tanks. Similarities with the overturning effects caused by wind and seismic loading are identified. The possibilities of axial buckling and shear buckling are investigated, and allowable stresses are discussed. For anchored tanks, the effects of tilt on the shell hold-down anchors are shown to be significant, and for unanchored tanks the possibility of shell uplift is discussed. A diagrammatic representation of the results is presented which allows stresses caused by tilt to be compared with stresses caused by other tank loads and the prediction of stresses caused by future tilt.
Experimental tests on a model open-top tank are reported, and indicate that tilt did not cause significant distortion of the tank.
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