Strength and stability of locally supported cylinders
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Date
2007Author
Doerich, Cornelia
Metadata
Abstract
Large quantities of particulate solids and fluids are stored in cylindrical metal shell
silos and tanks with a vertical axis. Such metal silos and tanks are often required to
be elevated above ground level to permit trains, trucks or conveying systems to be
placed beneath a hopper from which the solid or fluid is withdrawn. Elevated silos
must be supported, and access requirements often mean that the supports must be
local (either on columns or supported from an elevated floor system).
The connection of a local support to an elevated cylindrical metal silo shell is a longstanding
difficult problem in shell analysis, and most designs are based on simple
ideas using past experiences of successes and failures. Smaller silo structures are
often supported on local brackets attached to the side of the shell, but very few
investigations of the behaviour or strength of such an arrangement have ever been
made.
This thesis presents a comprehensive investigation into the behaviour of a cylindrical
steel shell that is discretely supported on several brackets, each rigidly connected to a
stiff column or floor. The study has been conducted within the framework of the
European Standard for Shell Structures (EN1993-1-6, 2006), which requires that the
two reference strengths of the small displacement theory plastic collapse resistance
and the linear bifurcation critical elastic resistance should both be evaluated to
establish the context in which more sophisticated analyses are judged, and to provide
a rapid means of producing reliable but simple design information.
Therefore this thesis begins with a thorough investigation of the predictions of these
two reference strengths for these structures, discovering the challenges inherent in
this methodology and finally developing equations that can be used in hand
calculations intended for the simple evaluation of the reference strengths for a wide
variety of geometries. The influence of geometric nonlinearity is next explored, both
with and without geometric imperfections. The results pose some interesting
questions concerning the relative importance of geometric nonlinearity and
geometric imperfections in shell buckling problems where the stress field is far from
uniform. In the final part of the investigation, analyses are conducted that include
both material and geometric nonlinearity with and without geometric imperfections.
The results of these analyses are presented and analysed in the context of interaction
capacity curves.
Following this extensive parametric investigation using linear and nonlinear analyses
of all kinds, design recommendations are formulated so that bracket supports of this
type can be used on thin cylindrical shells of any thickness and with any bracket
dimensions necessary to transmit the loads. Finally, proposals are made for key
future research investigations.