The weight reduction requirements of industrial vehicles force engineers to choose materials, geometries and manufacturing methods that lead to the most favorable strength/mass ratio. Consequently, fatigue resistance takes an important place in the dimensioning of structures in order to ensure a recommended service life. The quality of the predictions given by the usual fatigue criteria strongly depends on the precision with which the in-service stresses are calculated. For welded joints subjected to cyclic loads, the in-service stresses depend on the residual welding stresses and their evolution during the loading cycles. If the loading cycles lead to plasticization of the structure, the latter can then reach an elastic or elastoplastic stabilized state which can be linked to the behavior of the material itself or to certain combinations of primary and secondary loadings. This work relates to the study of a mechanical element in S355 steel belonging to the French brand Haulotte. The research carried out on this type of element is focused on articulation pivots, subjected to strong stresses. According the experimental observations, there is no doubt that fatigue-type problems on the weld seams are present. Thus the development of a multi-phasic numerical model made it possible to calculate a stabilized cyclic state as well as to estimate the life time in oligocyclic fatigue conditions. These results could be verified by comparing them to experimental tests carried out on real parts.