Fatigue assessment of welded joints in large steel structures: a modified nominal stress definition

According to the notch stress intensity factor (N-SIF) approach to the fatigue assessment of welded joints, the weld toe and the weld root are modeled as sharp V-notches. The N-SIFs quantify the intensity of the elastic stress field near the points of singularity and capture not only the weld shape effect, but also the size and the loading condition (membrane and bending) effects. The computational effort required to evaluate the N-SIFs, due to the necessity of very refined meshes, is a strong limitation in megastructures application. This limit can be overcome estimating notch stress intensities through the strain energy density (SED). Here, a SED based modified nominal stress is presented and how to compute it by means of a finite element analysis is shown. The effect of loading condition (membrane and bending) is addressed by introducing a proper coefficient obtained linking local concepts to the classical nominal stress components. Then, the implications in fatigue design of large steel structures are discussed.