3D Modeling Issue with Hat Channel members (Purlins) failing due to being an open section.

Question

As noted in the subject title, I'm having issues with getting the hat channel members (purlins) to pass in my 3D model. The members pass if I do a bending check by hand using the same gravity load and section modulus shown in the model (Sy=Iy/c). As you can see I assigned one of the purlins to be a 1"x1-14ga tube steel member to check and see if it would pass. I picked this section due to it having similar section properties as the hat channel except it is a closed shape. Any advice on how to analyze the hat channels in STAAD so that they are only seeing axial bending from the gravity/uplift loading would be greatly appreciated. Also, please address any other errors you may notice in my model. 
 P.S. I did reference Section F.1 of the Steel Manual to check and see the failure mode that the hat channel was under, but I didn't get much context from the section. Also, the actual building will be 100' long and have 26 frames, I attached only a 3 frame section for simplicity. Thank you! 
 100x (1.5' & 3' Chord Spacing) Frame.STD

Modestas · Answer

UPT sections which have a General type are designed as an approximated I section in STAAD.Pro. STAAD does not design it as a Hat section or some other section (with the only exception for EN 1993-1-1:2005 code). Some more information can be found here: communities.bentley.com/.../612745

Modestas · Answer

I think the most accurate method would be to analyze the hat section as you do before, but design it manually by using the reported forces of the member. The closest approximation probably would be to create an equivalent UPT channel section and design it in STAAD.Pro. Of course, this would still be an approximation and I am not sure how similar the results to actual hat section design would be.