Current offshore inspection practice relies on the detection of gross damage, such as flooded member detection. Such an inspection philosophy relies upon the structure’s ability to withstand gross damage for an inspection interval based on the large reserve factors on the jacket design strength in both the undamaged and damaged conditions. This requires a demonstration of the structure’s strength in all of the possible damaged conditions with the most critical member removed. However, the load originally carried by the critical member is redistributed to other neighbouring members which must consequently have an impact on the design fatigue lives of other members and increase the probability of more members failing. Ignoring the effects of stress redistribution due to member failure could therefore result in under-prediction of the probability of a second member failing and hence an optimistic prediction of platform reliability. This paper aims to quantify the effects of stress redistribution on the prediction of platform reliability. Stress and ultimate strength analyses were performed on three platforms in 45m water depth with bracing configurations of varying structural redundancies, namely, single diagonal, inverted K and X-braced, to calculate the stress enhancement in all members due to the individual failure of all other members. These stress enhancements were input into probabilistic fracture mechanics models to calculate the increase in failure probability of these second members due to the failure of a first member. More than 1000 pushover analyses were performed to calculate the ultimate strength of the structures in all single-member failed conditions and many hundreds of dual member failed permutations for each jacket. A cross-correlation of the most significant stress redistribution results and pushover results was used to perform platform reliability assessments. The effect of including stress redistribution and dual member pushover results was shown to reduce the predicted platform reliability for all bracing configurations, mainly due to a number of dual-member failed conditions that weakened the jackets significantly. It is recommended that, in addition to performing single member failed pushover analyses, there is a need to assess dual-member failed conditions that drastically reduce platform strength.

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