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Ideal Location of Intermediate Ring Stiffeners on Discretely Supported Cylindrical Shells

2014-04-01
Topkaya, Cem
Rotter, J. Michael
Silos in the form of a cylindrical metal shell are commonly elevated to provide access to the space beneath, permitting the contained materials to be directly discharged. A few discrete column supports at evenly spaced intervals are commonly used. However, the structural design of discretely supported cylindrical shells presents a variety of challenges. The presence of discrete supports results in circumferential nonuniformity in the axial compressive stress as well as a progressive vertical decay above the support. Several approaches can be adopted in design depending on the severity of the nonuniformity of the stresses. Relevant research to date has focused mostly on the behavior of cylinders supported on brackets, local forces at the base, or stiff ring beams. The use of intermediate ring stiffeners to provide circumferential uniformity in the axial membrane stresses has long been recognized, but few studies have given a clear view of the practical requirements for such rings. In this paper, a combination of base and intermediate ring stiffeners is explored to develop a practical and cost-effective solution that leads to more uniformity in the axial membrane stresses above the intermediate ring stiffener. For the purposes of obtaining a simple analytical solution, the cylindrical shell is subjected to the fundamental harmonic of the column support and analyzed using membrane theory. It is shown that an ideal location exists for an intermediate ring stiffener such that the axial membrane stress above this ring is circumferentially completely uniform. The ideal location of this ring is determined analytically and is expressed in terms of the basic geometric variables. This ideal ring location is then independently verified using many linear finite-element analyses. A further study explores the effect of placing the intermediate ring stiffener below the ideal location. The results are presented in a manner that makes them suitable for direct adoption into traditional design specifications. (C) 2013 American Society of Civil Engineers.