ABSTRACT:

This paper is concerned with the optimum design of stringer-stiffened cylinder found in tension leg platforms based on the component reliability. In the context of structural design, a major goal is to achieve a balanced design between safety and cost, that is, the design should probably based on the structural reliability. The total cost is minimized, which is composed of the structural cost and failure cost, with constraint on the allowable reliability index and some design requirements drawn from various design codes. The numerical results with varying the number of design variables considered in the optimisation procedure are derived and optimum designs are compared with the minimum weight designs from the view point of safety. The present results provide a more efficient design than the rule-based design in use at present and it is drawn that the minimum weight design may lie on the unsafe side. The paper ends with a discussion of the present results and an extension of the concept toward a more economically efficient design of such kind of structures.

INTRODUCTION

In view of the inherent random nature of the loading and the strength as well as the imperfect structural analysis and load estimation, the structural optimization needs to be based on the structural reliability. the last two decades we have seen much work on the reliability- based optimum design linked with the classical deterministic optimisation formulations. It has been proposed for some times that a more rational criterion for structural design is that safety be represented by the reliability or alternatively at the failure probability of a structural, and hence the reliability constraint should likely be included in the re-design and the optimisation process to get a more efficient design (Kishi et al,1985, Frangopol,1985, Corotis and Soltani,1985).

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