Comparative Study of Fatigue Life Assessment Made by Different Approaches

The fatigue life of steel elements is usually predicted by classical nominal stress method. Such approach is very convenient, when design model of structure is based on bar elements. But the level of analysis in steel structures is still increasing. There are used more and more sophisticated FE packages, which offer shell and 3D elements instead of classical bars modeling. They allow to include real shape of elements and existence of welds, bolts and other joining components. Results obtained from such analysis contain many stress raising effects and can be easily utilized in modern approaches of fatigue life based on local stress values, e.g. structural (hot spot) stress method. Development of modern computational FE packages make prediction of fatigue life using local approaches possible and easier. Major obstacle in wider application of numerical methods for the fatigue assessment of steel structures is apprehension of designers about accuracy of local approaches. The focus of presented research has been on comparison of fatigue life predictions based on nominal stress method and on structural stress method, made for a couple of constructional details. Paper presents influence of geometrical parameters on stress concentration factors and also highlights a wider flexibility of structural stress method.