In this paper, we deal with finite element modeling techniques for the dynamic behavior of sheet metal structures jointed by spot welds. A major requirement of spot weld finite element models is to accurately predict the dynamic characteristics of welded structures with a small number of degrees of freedom. In addition, spot weld models are easy to generate for non-congruent meshes of the jointed metal sheets. For this purpose, a model using multi-point constraint (MPC) is widely used in the automotive industry. For the model using MPC, we investigate the effect of mesh size in the area of the spot weld (patch area) on the modal properties such as natural frequency and mode shape. As an example structure, the structure that consists of two steel plates jointed by three spot welds is used. The results indicate that the proper shell element size in the patch area is dependent on the solid element size determined from the diameter of a weld nugget. The recommended range of the ratio of sizes of the shell to the solid elements is between 1.0 and 1.5.
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