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|Title:||Stability and strength of steel silo transition junctions|
Hong Kong Polytechnic University -- Dissertations
|Publisher:||The Hong Kong Polytechnic University|
|Abstract:||Large elevated steel silos for the storage of bulk solids generally consist of a cylindrical vessel above a conical discharge hopper supported on a cylindrical skirt. The cone-cylinder-skirt transition junction is subject to a large circumferential compressive force and a ring is often provided to strengthen the junction. The strength of the junction may be limited by either axisymmetric plastic collapse or non-symmetric buckling. A review of the existing literature reveals that all previous studies on steel silo transition junctions have been theoretical and have not addressed a number of important aspects including the effects of geometric imperfections, residual stresses and the stiffness of the stored bulk solid. This thesis thus presents a combined experimental and theoretical study aimed at experimental verifications of existing theoretical models and results, and clarifications of the effects of various factors ignored in previous investigations. A sophisticated experimental facility is first presented. This was developed as a multi-purpose test rig for shell buckling experiments with special attention to the testing of steel silo transition junctions. This facility included a loading frame, a rotating measurement frame supporting a laser displacement meter for accurate geometric imperfection and deformation surveys, and necessary equipment for the fabrication of quality test models from thin steel sheets. The experimental program of the present study consisted of three series of tests: the CC series on cone-cylinder junctions under internal pressure, the CCS series on cone-cylinder-skirt junctions under bulk solid loading and the CCSR series on cone-cylinder-skirt-ring junctions under bulk solid loading. The theoretical work of the present study consisted of numerical analyses conducted using the NEPAS program for nonlinear elastic-plastic bifurcation analysis of shells of revolution and the general purpose commercial package ABAQUS. The numerical analyses enabled the development of suitable modelling procedures for the test junctions and provided further insight into structural behaviour, thereby maximising the benefit of the experimental program.|
Four tests were carried out in the CC series, with one of them being a ring-stiffened cone-cylinder junction. These tests are believed to be the first carefully conducted buckling experiments on such junctions. Development of strains and deformations in the model junctions are carefully examined, with both imperfection and deformations interpreted by Fourier decomposition. These tests not only provide useful data for calibrating numerical models of steel shell junctions without the uncertainty associated with bulk solid loading, but also address a buckling problem of importance to the design of pressure vessel and piping components. Nonlinear bifurcation buckling analyses based on the perfect geometry and nonlinear analyses using both measured and eigenmode-affine imperfections were carried out for all four model junctions. A rational finite element model established through these numerical simulations was then deployed in a parametric study on cone-cylinder junctions covering a wide range of geometry. A design proposal in the Eurocode format is proposed for practical use. As all previous buckling studies on silo transition junctions have been concerned only with the buckling of rings, the tests of the CCS series represent the first investigation into buckling in transition junctions which do not feature a ring. Four models were fabricated in this series, but one of them could not be loaded to failure within the capacity of the loading frame due to unexpected over-strength. The CCSR series consisted of five tests and is the first experimental study on cone-cylinder-skirt-ring junctions in steel silos. Geometric imperfections and deformations are presented and interpreted by Fourier decomposition to study the development of buckling deformations. Development of strains and failure modes are carefully examined. For junctions with a ring, methods for the determination of experimental buckling loads based on displacement measurements on the ring are presented. Nonlinear bifurcation buckling analyses were carried out for model silo transition junctions using the nominal perfect geometry. Both the buckling loads and the buckling modes are compared to experimental results. Nonlinear analyses were also performed using both measured and eigenmode-affine imperfections. The effects of a number of factors on the load carrying behaviour of transition junctions are investigated, including the distribution of pressure in the model junction, the effect of welding on yield stress, and the welding deposit at the transition. The effect of ring/junction buckling on the load carrying capacity of transition junctions and the imperfection sensitivity of these junctions are also examined.
|Description:||xiv, 421 leaves : ill. ; 30 cm.|
PolyU Library Call No.: [THS] LG51 .H577P CSE 2001 Zhao
|Rights:||All rights reserved.|
|Appears in Collections:||Thesis|
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