Trying Datasmith to import files from AutoCad and Prosteel

Hi everybody. I was trying sometimes to export steel structures from Autocad. It did no worked and now with Datasmith I decided to try it again.
I am using Autocad with one Plugin (Prostructures) I can import the file but it is empty on Unreal. Which is the best option to do that? 3DS would be a pain in the ■■■ if I have to detail everything there but with 3DS I can import the files.

best regards

Really I have no idea but I think surfaces. How can I know that?
Now I am exporting as FBX, importing with 3DS to export again the FBX…
But something is not working (I am really noob with Unreal Engine)
But Unreal is burning my 16gb RAM with a small structure.