Jacket Reliability Design Considering Interacting Limit States

The reliability of jacket structures is addressed by considering inter-relationships between ultimate strength, fatigue and progressive collapse limit states, for both intact and damaged structural configurations and a range of defect and collapse events, including accidents and gross errors. Simple robustness criteria for use in design are suggested based on the ratio of damaged-to-intact probabilities of failure, a progressive collapse indicator and damaged strength ratio (DSR) values. Their practicality is illustrated by detailed reliability assessments of two quite different jacket structures — a major 6-leg platform and a shallow water tripod. The strong interdependence between robustness and quality requirements is demonstrated, as is the potential importance of fatigue-driven progressive collapse for certain structures.