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Abstract
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In general, duplicative redundancy of load carrying connections/fastenings occurs naturally in design. This is due to the fact that connector units frequently have upper size limitations set by manufacturing processes or quality assurance. Large, highly loaded, demountable vessel flanges could not sensibly or practically be held together with a very small number of bolts as is the practice for small bore auxiliary pipework.
Operational inaccessibility tends to foster the introduction of perhaps more structural redundancy than would have evolved naturally in deterministic design processes. Such contrived redundancy aims at achieving a higher structural reliability, not only during initial operation but subsequent to anticipated degradation of the feature during life which in extreme cases might remain undetected or prove even undetectable.
This paper examines what is no doubt one of the most common forms of load bearing connection, namely an annular array of a single type of connector unit. A structural reliability assessment procedure is outlined for such a system in both initial and possible subsequent degraded states. The application of the method to separate examples of low and high redundancy is set out in detail.
Results of the study suggest the need to optimise the structural reliability during such designs to reduce where practicable over-redundancy in large constructions but on the other hand to ensure that, for cases where low redundancy is a natural choice, the achievable reliability standard is in line with functional requirements. |