# Why should a beam structure be meshed with structural elements?

We are talking about this kind of structure:

You have a solid CAD file of this structure. What do you do: use beam elements, extract mid-surfaces to mesh it with shell elements, or directly mesh the solid 3D CAD file with tetras (the “quick and dirty” approach)? Does the tetra mesh will be able to catch bending of the beams? There is only one way to answer this: try it with different mesh sizes. The study I did for this particular model (linear elastic analysis) told me that using 2 quadratic elements in the thickness results in an error of 5% on the displacement and 4% on the stress (compared to the same structure meshed with shells).

The problem with this approach? The mesh of this structure has a total of **3 millions nodes** using the tetra mesh. So, the choice between shell or solid Idealization for this kind of structure is a balance between calculation time and effort needed to transform the solid CAD into a surface model. Good practice with this kind of structure is usually to use structural elements like beams or shells.

If the shell approach is chosen, Inventor NASTRAN has a very good tool to extract the mid-surfaces: