Importing Solid Elements

[MaraQ]

I'm trying to import a structure as solids into SAP2000 v16, and I'm having some issues. My supervisors want me to import an Inventor or SolidWorks solid object into SAP. My current process is to import the solid into AutoCAD and save it as a DXF for import. The problem I encounter is getting the solid into 3D polygon meshes in AutoCAD that will show up as solid elements when imported to SAP (see example "Pyramid Base.dxf" on this site for a file that works for me). Has anyone had luck in importing solids into SAP2000, either from AutoCAD .dxf files or other? I've approached it from the AutoCAD standpoint, but support and forums are also stumped.