4R METHOD FOR CONSIDERATION OF THE FATIGUE PERFORMANCE OF WELDED JOINTS – BACKGROUND AND APPLICATIONS
Timo Björk *, Antti Ahola and Tuomas Skriko
Laboratory of Steel Structures, Lappeenranta University of Technology, Lappeenranta, Finland
Fatigue strength capacity is an important design criterion when structures are subjected to fluctuating loading. However, current official design methods do not consider all the essential factors that can have a significant influence on the fatigue performance of a welded steel construction. Such factors are: the ultimate strength of material, residual stresses, stress ratio of external load and local geometry at the critical point of structure. The new 4R method, which is based on the modified effective notch stress (ENS) concept, provides a novel way to consider these factors efficiently. The 4R method enables designers to use default values of parameters based on previous experience, or the parameters can be measured using simple and widely known methods. This paper presents the latest developments in the 4R method and provides important insights into the engineering applications of the method. The 4R method is a promising approach to determining the potential performance of high and ultra-high strength steels (UHSSs), as well as the role of mean stress and the effect of post treatments, such as mechanical peening, on the fatigue capacity of welded joints.
Fatigue design; Welded joints; Ultra-high strength steel; 4R method