Hello Maxime,

Sorry for the delay in replying.

Yes, you don't get von Mises Stress plot for beam elements.

On Solution you can Probe > Beam > Axial Force and Shear Force.

On Solution, right click to Insert > Beam Tool.  Then in the Beam Tool, right click to Insert > Maximum Combined Stress.  This is the Axial Stress combined with the Bending Stress.  You can also just plot Direct Stress = Axial Stress.