TABLE OF CONTENTS The determination of the loading and related stress histories that a structural detail will be subjected to during service life plays an important if not the most important role in achieving a reliable fatigue life estimate. It must be borne in mind that the number of cycles to failure is a function of the stress range level raised to a power of at least 3 for welded steel joints. This means that if the stresses are underestimated by, say, 20%, the fatigue life will be close to 100% overestimated.
There are three major topics regarding service life stress history:
the loading scenarios have to be assumed at the design stage for say 20 years into the future;
the loading is often random by nature, e.g. wave loading for structures at sea;
the response calculation and stress analysis leading from the applied forces to the stress response in the vicinity of a weld is often based on approximations.
Regarding the first point, it is obvious that movable structures may possibly change operating area and operational conditions during the course of their service life. An example is large tankers for oil transport at sea. There is a large difference between the wave-induced loading in the Pacific Ocean and the North Atlantic during wintertime. The second point is usually treated by stochastic methods which we will include in this chapter. The last point is a part of load modeling and stress analysis. It is...
