Fatigue design of complex welded structures

This paper is concerned with the design of complex welded structures subjected to fatigue loadings. In the last years it has been developed a new approach for predicting the high cycle fatigue behaviour of welded joints, based on the Notch-Stress Intensity Factors of the uncracked geometries, which have been successfully applied to welded joints of different geometries using an analytical frame in combination with stress data obtained from Finite Element Analyses. The approach is based on the observation that the very small weld toe radius obtained by using traditional welding technologies is consistent with the assumption of a sharp V-notch geometry, characterised by an exponential stress field, which the fatigue strength depends on. Recently published Eurocodes suggest the use of a hot spot approach, both for steel and aluminium structures. Nevertheless the evaluation of fatigue strength of engineering complex structures remains a difficult and, in some way, controversial subject. We hope that this synthetic presentation of the N-SIF and hot spot approaches as compared to the European Standards could help to clarify the subject and to design better and more reliable structures.