|Title:||Buckling of T-section transition ringbeams in elevated steel silos and tanks|
Building, Iron and steel
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Civil and Structural Engineering|
|Pages:||xiv,  leaves : ill. ; 31 cm|
|Abstract:||Elevated steel silos for the storage of bulk solids or elevated steel tanks for liquid storage commonly consist of a cylindrical vessel above a conical hopper (or end closure) supported on a skirt or a number of columns. The point of intersection between the cylindrical vessel and the conical hopper is often referred to as the transition. The transition junction formed by the intersecting shell segments is subject to a large circumferential compressive force which arises from the radial component of the meridional tension in the hopper. A ring is generally provided at the junction to resist this compressive force. As this ring is a main structural member rather than a relatively light stiffener used on a flexible shell wall, it is referred to as a ringbeam in this thesis. This transition ringbeam may be a simple annular plate, but in many cases a stiffened annular plate in the form of a T or angle section is preferred due to their higher out-of-plane bending stiffress. Under the large circumferential compressive force, the ringbeam may fail by buckling. In-plane buckling involving flexure only is generally prevented by the adjacent shells, so out-of-plane buckling failure is usually the critical buckling mode. The out-of-plane buckling mode consists of an overall rotation of the ringbeam cross-section around the point of attachment (the inner edge of the ringbeam) with associated distortion of the cross-section. A review of the existing literature reveals that the elastic and plastic out-of-plane buckling strengths of annular plate transition ringbeams have been studied extensively, and design rules have been proposed. Much less has been done on T-section transition ringbeams. Previous studies on T-section ringbeams have been concentrated on the flexural-torsional buckling strength, treating the ringbeam cross-section as rigid during buckling. This however overestimates the buckling strength, particularly for ringbeams with a heavy rotational restraint from the shell walls. Furthermore, the effect of material yielding on the buckling strength has received limited attention. This thesis thus presents the results of a major study to correct current deficiency in our knowledge on the buckling behaviour and strength of T-section transition ringbeams. The comprehensive theoretical/numerical investigation presented here has been carried out with the aid of an advanced finite element program NEPAS, which can perform linear or non-linear bifurcation buckling analysis of elastic or elastic-plastic branched axisymmetric shells. The work consists of four parts. The first part is concerned with the development of an elastic buckling strength approximation for inner edge clamped T-section ringbeams. This is achieved through a careful examination of extensive numerical results and by making use of the existing solution of Bulson for edge stiffened plates under axial compression. Part two of the work deals with the elastic buckling strength of inner edge simply supported ringbeams. An existing closed form solution for this case is substantially simplified without sacrificing its accuracy. The third part is aimed at developing an elastic buckling strength approximation for T-section ringbeams with an elastic rotational restraint from the adjacent shell walls. This buckling strength is formulated through an interpolation of the buckling strengths of the two limiting cases investigated in the first two pads, following the approach adopted for annular plate ringbeams by Jumikis and Rotter. Their interpolation function for annular plate ringbeams is found to be satisfactory also for T-section ringbeams. Finally, the effect of plasticity on buckling strength is investigated, leading to the development of a design proposal for the buckling strength of steel T-section ringbeams in elevated silos and tanks. Application of the design method is illustrated through an example.|
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