|Title:||Buckling of cylindrical shells under non-uniform stress states|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Shells (Engineering) -- Testing
Cylinders -- Testing
Strains and stresses -- Measurement
|Department:||Department of Civil and Structural Engineering|
|Pages:||xiii, 340 leaves : ill. ; 30 cm|
|Abstract:||Cylindrical shells under non-uniform stress states are widely found in shell structures such as steel silos and tanks. A review of the existing literature shows that there is only limited research on the buckling behavior and strength of cylindrical shells subject to non-uniform stress states. Simple stability design methods are also not available for most problems of this type. This thesis thus presents a series of numerical investigations into the buckling behavior of cylindrical shells under various non-uniform states of stresses, culminating at a comprehensive study of the behavior of circular cylindrical silos subject to eccentric discharge pressures, which is one of the most important non-uniform loading conditions for civil engineering shell structures. The work presented here was carried out to advance the existing knowledge on three fronts for cylindrical shells under non-uniform stress states: (a) appropriate numerical modeling techniques for shells with assumed geometric imperfections; (b) sensitivity to geometric imperfections of various forms and amplitudes; and (c) the structural consequences of patch loads in silos which are commonly specified to represent the effect of discharge eccentricity in silo loading codes. All numerical work was conducted using ABAQUS which is a powerful and well-known general-purpose finite element program popular with shell buckling researchers. Following an introduction to the subject and a historical review of relevant literature. Chapter 3 presents a numerical investigation into issues associated with the use of various symmetry conditions. The performance of half-structure models, half-wave and whole-wave sector models in representing the behavior of shells of revolution subject to a radial ring load with eigenmode-affine imperfections is examined. The effect of solution steps on the predicted response is also discussed. During this investigation, a strange type of spurious modes was observed. A study of these spurious modes is presented is Chapter 4. The causes for these spurious modes are identified; remedies to suppress them are suggested. Based on the work presented in Chapters 3 and 4, a reliable numerical model was employed to study the buckling and postbuckling behavior of shells under partial axial compression. The attention is focussed on the sensitivity of such shells to four different types of geometric imperfections: linear bifurcation mode, nonlinear bifurcation mode, three postbuckling deformation patterns and weld depressions. One important application of shells in civil engineering is as silos for the storage of bulk solids. A major issue in the design of steel silos requiring urgent research is the structural consequence of eccentric discharge pressures. The effect of discharge eccentricity is represented in loading codes through the specification of patch loads. In Chapters 6-8, results from rigorous numerical analyses of steel silos subject to eccentric discharge wall loads predicted by four different but well-known loading codes are presented and carefully interpreted. It is shown that although the patch loads as specified in current codes differ greatly from each other, they have little effect on the buckling strength predicted by a nonlinear analysis that takes into account the effects of geometric nonlinearity, imperfections and material yielding. Results from other types of analyses are also presented and interpreted using recommendations given in Eurocode 3 for the conversion of numerical results into buckling resistance for design use.|
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