Answer:
There are two options for doing this:
1. Modeling as a folded plate structure (see Image 01)
2. Modeling as an orthotropic surface (see Image 02 and Image 03)
The first option is only useful if the stresses in the trapezoidal sheeting are of interest. The individual corrugation is to be modeled using surfaces. The modeling and calculation effort is very high. You can facilitate the modeling slightly: The cross-section library of RFEM contains all common trapezoidal sections. Create a member with a trapezoidal cross-section. Then, generate surfaces from the member using the corresponding shortcut menu option. You can then modify or copy the created surfaces with trapezoidal sheeting.
If the stiffness of the trapezoidal sheeting is only relevant to the analysis, it is reasonable to use modeling as an orthotropic surface. When defining the surface, select the "Orthotropic" stiffness type. Use the [Edit Parameters] button next to the list box to define the orthotropic properties. The stiffnesses can be described by the equivalent thicknesses or directly by the coefficients of the stiffness matrix (see the manual). You can specify any angle for the orthotropy direction, which is related to the local surface axis system. This angle can also be checked graphically (Display Navigator: "Model → Surfaces → Orthotropic Directions").
