Recent developments in reliability analysis to aid structural design and reassessment during use as well as inspection planning are reviewed. Data and methods applied to calculate the probability of ultimate and fatigue failure of structural components and systems, considering the effect of inspection, are critically examined. Target reliability levels are briefly discussed.
The harsh environmental conditions and other hazards associated with offshore structures as well as the significant consequences of failure make safety an important consideration for such structures. Offshore platforms are designed for a service life of 20 years or more, with criteria for serviceability and safety against structural failure and overall instability or possible sinking (see e.g. ISO 1994-). Adequate structural safety is achieved by applying ultimate (ULS) and fatigue (FLS) limit state criteria for components. Fatigue is an important consideration for structures in areas with more or less continuous storm loading (such as the North Sea) and especially for dynamically sensitive structures. Progressive collapse limit state (PLS) criteria are applied to avoid catastrophic accidents, i.e., due to a small damage. In addition to design measures inspection and monitoring, and repair, if necessary, are important measures for maintaining safety, especially with respect to fatigue, wear and other deterioration phenomena. But their effect on the reliability depends upon the quality of inspection, e.g., in terms of detectability vs. size of the damage. Hence, an inspection and repair measure can contribute to the safety only when there is a certain damage tolerance. This implies that there is an interrelation between design criteria (fatigue life, damage tolerance) and the inspection and repair criteria. Up to now, however, this interrelation has not been explicitly considered, due to lack of methods tO deal with this problem in a rational way.
