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This study discusses activities developed in order to create a new designmethodology for automotive welded structures under complex loadings. Thismethodology associates a fatigue criterion, to predict fatigue limits, and a damagemodel to treat finite fatigue lifetimes. In a first step, the pertinence of the proposedfatigue criterion is evaluated under an automobile multiaxial load spectrum. This phaseis performed using 1045 steel cylindrical specimens to identify material behavior.Linear damage accumulation seems not sufficient to simulate correctly fatigue lifetime.A new incremental damage model is thus introduced that fits better experimental data.The second step studies weld behavior. A welded specimen is designed to representmaterials and manufacturing process of automobile chassis parts. A finite elementmodel, based on a macroscopic study and instrumented tests, was created. This part ofstudy will permit to transpose the methodology developed in the first step to weldedstructures.