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RR494 - The significance of stress redistribution effects on structural reliability of deepwater jackets

A previous study highlighted the possibility that ignoring the effects of stress redistribution due to member failure in jackets could result in an optimistic method for predicting platform reliability. This was shown to have the greatest effect in lower redundancy structures, but the effect was not proven. A second study [2] quantified in more detail the effects of stress redistribution in causing dual member failures on the predicted platform reliabilities. Both studies concentrated on shallow water platforms.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.

The present work was performed to extend the work on stress redistribution to consider jackets in greater water depths. Therefore, three different deep water jacket models were developed. The jackets were based on the same baseline structure and designed for the same Northern North Sea location but with different bracing configurations, namely X-braced, K-braced and diamond braced.

The effect of including stress redistribution and dual member pushover results was shown to reduce the predicted platform reliability for all bracing configurations. This reduction was by more than two orders of magnitude.

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Updated 2010-03-19