The relatively complex geometry of welded joints makes an assessment of fatigue strength rather difficult in many cases, especially if the common nominal stress approach is applied. An alternative to this method is the hot spot stress approach which considers structural stress concentration factors at a welded discontinuity, in which a unified S-N curve is used to estimate fatigue strength, rather than using numerous curves corresponding to welded joint categories of welded structures. In this paper, using numerical and experimental results for a variety of welded joint models, a unified S-N curve was derived, which is independent of structural stress concentration factors. Based on a fatigue test of a real welded joint in a train bogie frame, it could be confirmed that the unified S-N curve can be directly applied to the estimation of fatigue strength and fatigue design for general welded steel constructions.
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