Abstract

Fatigue design of large welded structures presents significant challenges due to complex geometries and variable loading conditions, especially in industries such as offshore engineering. While nominal stress-based methods remain widely used, they often fall short when applied to intricate welded details. This study investigates the use of MAGNA FEMFAT, a commercial fatigue analysis tool, to evaluate the fatigue strength of large welded K-nodes typically found in small offshore platforms. Three finite element models—using both 3D shell and solid elements—were developed in Ansys Mechanical and analysed with FEMFAT using its Shell WELD, Solid WELD, and R1MS fatigue assessment approaches. The fatigue life predictions were compared against experimental data from the literature. Results highlight the effectiveness of FEMFAT in automating fatigue post-processing and delivering fatigue life estimates that correlate well with observed experimental performance, demonstrating the tool's value for efficient and reliable fatigue evaluation in complex welded structures.