Reliability‐Based Progressive Fatigue Collapse

General relationships between individual joint reliability and overall system reliability in a redundant structure with no repair program are presented. Using a fatigue reliability model, a Monte Carlo analysis provided a distribution of time to failure for various degrees of redundancy. Random variables in the model account for uncertainty in the process of determining fatigue strengths of the joints. The distribution parameters for these random variables are representative of welded tubular joints in offshore platforms. Figures are shown which relate the target safety index of a joint to the reliability against various definitions of “functional failure” of the structure. Also included is an example of how the probability of a second failure occurring within a specified time interval after an initial failure can be predicted. This can provide insight in determining the necessary frequency of inspections.