Creating Frame Section From .dxf import

[KBHStructural]

I'm trying to create a frame section by importing a .dxf file of a concrete box girder for a bridge. When I import the file it only gives me the option to have the lines be turned into plates, thus the resulting section is just the outline of my box, built up with plates.

I'm looking to have the imported file create a solid section with an opening. My .dxf is included.

Any help is appreciated.