I wonder how the degrees of freedom are organised on the eliminated stiffness matrix exported from a 3D structure composed of shell elements. The structure has no constraints, as I want the free-free frequencies and mode shapes, then I was expecting eliminated mass and stiffness matrices of size equal to the (#degrees of freedom) = (#nodes) * (#dependent variables). However the eliminated matrices have a size equal to (#nodes) * 5.
I know shell elements nodes have only 5 degrees of freedom, but since they are not on the same plane, I was expecting 6 degrees of freedom per node, not 5. If someone can explain-me how this matrix is organised, I would be very grateful :)
Best regards,