Taking the model composed of channel steel and ribs as an example, the model is simplified to a shell model for calculation. The specific steps are as follows:
1.Build a model
Select DM to build a model of the composition of channel steel and ribs, or import it with other 3D software. In DM, the channel plane and the rib plane are drawn separately in the two sketch planes for the extrusion operation. Then, choose to line the ribs. Eventually, the following model is generated.
2.Model processing
Use the surface-mid extraction to shell the model, and after shelling, all shell models are combined into one. Use the Surface Extension to fill the gap between the channel and the ribs.
3.Meshing
With all the default settings, you can see in the figure below that the channel and ribs shown in the model are continuous.
4.Boundary conditions
Add fixed support to the bottom surface of the channel steel, and load pressure on the top of the channel steel with a size of 5MPa.
5.Solve Add equivalent stress, total deformation, and analyze the calculation results.
Deformation phase diagram. 
Stress phase diagram. The advantages of using shell elements: fast solution, no thickness requirements, less calculation of structural data, easy to obtain reaction forces and reaction moments. Special attention should be paid to the surface extension of the shell element to fill the gap between the surfaces.