Fatigue design of weldments using the finite element method – Background and validation of Eurocode EN 1993–1-14

The application of the finite element method (FEM) in the design and assessment of steel structures has become increasingly widespread among structural engineers. For fatigue design of steel structures, it becomes natural – when complex finite element models are created to assist the design – to also perform fatigue verification on the basis of the results obtained from the FE models. Two methods are particularly interesting in this regard; the Hot Spot Stress(HSS) and the Effective Notch Stress (ENS) methods. Until recently, the Eurocodes for steel structures offered limited guidance on implementing these two methods in fatigue design, although detail categories for the HSS methods have been available since the early iterations of EN 1993–1–9. In connection with the development of the 2nd generation of the Eurocodes, EN 1993–1–9 has been updated to include detailed rules on representation of fatigue resistance in the HSS and ENS systems, while the new EN 1993–1–14 developed to provide guidance on the construction of FE models and evaluation of load effects obtained from FE-analysis. This paper reviews the background of these two FE-based fatigue verification methods as stipulated in the updated Eurocodes, contrasting them with the conventional Nominal Stress method. Their respective advantages, drawbacks, limitations, and potential pitfalls are comprehensively discussed. Furthermore, a detailed worked example is provided to serve as a benchmark. The paper concludes that while the different fatigue design methods generally yield comparable results that align well with experimental data, critical exceptions exist where discrepancies between the methods are significant and deviate from test results.