The simulation of joints in structures of sandwich panels is very important in order to obtain values of the analytical natural frequencies and mode shapes that are in accordance with the experimental values. By means of a FEM program and an experimental set for modal analysis, different assemblies of sandwich plates in aluminium, fit together with corner joints, are tested. The FEM simulation of the corner joints is made in different ways and the comparison between analytical and experimental results shows that different methodologies of simulation can be applied. Interesting results on the influence of the element set forming the joint are obtained. Moreover the non-linear behaviour of the structures due to the thickness of the adhesive in the joint is analysed.