Discussion on the probabilistic assessment of fatigue with respect to reference periods

The paper covers the topic of time dependent reliability for fatigue assessment of engineering structures. As fatigue can be seen as a cumulative degradation process, time dependency has to be handled differently from failures caused by extreme impacts. Target reliability levels given in codes usually refer to the failure probability of a structure within a given time period, the so called reference period. In practical examples of fatigue assessment the consideration of the time period is often neglected, which leads to results not comparable with the target reliability levels given in codes. Also in 2015 an updated version of ISO 2394 (ISO 2015) code was published adding guidance for consideration of time-dependent fatigue assessment which will also be briefly discussed here. The consideration of time-dependency in this paper may not represent a novelty in the field of reliability analysis and employs fundamental methods. Still, as the topic is frequently ignored in probabilistic fatigue analysis examples, a short discussion might be of interest. The presented paper will (a) discuss the consideration of reference periods with failures caused by accumulating deterioration, (b) show comparative calculations based on a simple case study and (c) discuss the results.