This thesis presents a comprehensive study on the fatigue behavior of thin-sheet steel structures joined by seam welds, combining experimental testing and finite element (FE) simulations based on the meshing and fatigue evaluation methodology proposed by Fayard et al. The primary objective was to establish a reliable and practical workflow for the fatigue assessment of welded joints using conventional FE software—Abaqus and OptiStruct—without requiring specialized fatigue analysis packages. Experimental tests were performed on lap-jointed specimens made of 2 mm thick, 50 ksi steel plates welded using the GMAW-P process. The resulting force–cycle (F–N) data were converted into stress–cycle (S–N) curves using both maximum principal stress and an equivalent stress parameter derived from the Dang Van multiaxial criterion.