The Use of Shakedown Concepts in the Development of Design Rules for Shell Structures Subjected to Severe Cyclic Thermal Loading
From the shakedown and ratchet ting limit analysis of a wide range of thermal loading problems for axisymmetric thin shells it is evident that only a limited number of possible mechanisms of incremental collapse occur. As a result it is possible to develop simplified analysis procedures that can be used directly in the design process. This paper describes two such procedures. The first of these has evolved from the examination of the full range of interaction diagrams that are available, classifying them into groups and fitting simple equations to the shakedown boundaries. It has emerged that a simple conservative estimate of the elastic and plastic shakedown boundaries can be obtained by drawing a straight line on an interaction diagram whose intercept with the thermal loading axis is determined from the peak stress and the maximum membrane thermo-elastic stress. The second approach involves analysing each of the limited number of possible collapse mechanisms using the upper bound kinematic shakedown theorem. For each mechanism it is possible to obtain a simple expression for the shakedown boundary in terms of the major features of the thermo-elastic stress history which can be used as a basis of design code limits for thermally loaded thin shell structures. The extension of these techniques to creep effects is also discussed.
KeywordsInteraction Diagram Cyclic Thermal Loading Plastic Shakedown Incremental Collapse Isochronous Creep Curve
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