For verification, I only use commercial software, which I know very well. My model is a horizontal beam in bending; the tendons are in tension without bending, and the column is only in compression.
I used a hollow (box) profile for the horizontal member; it’s just rendered as solid after CalculiX run. The post is solid, like in the OP’s model. And the cables are square for the same reason.
Give it a try when you have some time. The FEM workbench in FreeCAD is far behind PrePoMax in most aspects, but it has 1D elements (trusses as well in the newest version, but they can’t be mixed with beams yet) and is very actively developed. It supports Elmer with electromagnetics and other multiphysics, too.
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I don’t see any empty profiles; there’s only a round pipe. There’s no rectangular one. Unless you modified the file using keywords. The result looks like it’s lifted. This can only happen if the lines were pre-tensioned.
Did you use an equivalent cross section?
What version of FreeCAD did you use to open it ? Box profile was added in 1.1.0 dev version (available as weekly builds for now) and I used it to prepare that file. It must convert the profile to a different one in older versions.
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Version 1.0. That’s why the 80x40 profile had a tiny dimension 
Yeah, FreeCAD 1.1 supports all beam profiles available in CalculiX apart from arbitrary (general) beam sections whose constants are entered directly.
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