Horizontal Window Mullion Analysis

[pajrengr]

I am performing a structural analysis of a horizontal window mullion comprised of two built up die assemblies spanning approximately 54 inches between supports. Each individual assembly is a combination of two aluminum extrusions connected by a thermal break. My main stumbling point right now is trying to determine how the wind load will be distributed from the glazing throughout the shape as a whole. I know bending between supports needs to be resisted as well as a torsional load due to the eccentricity of where the load is applied.

I have done mullion calculations in the past for closed aluminum members and simply combined the torsion and bending interactions together to check the member. With the multiple built up shapes I am having a difficult time determining how the mullion will resist torsion without being a closed member.

Attached is a sketch of the horizontal mullion section. Does anyone have any insight on how to complete the analysis?

 

[Archie264]

It looks to me like there are one or two additional assemblies, separated by thermal breaks. In any case, could you analyze each of the built up die assemblies separately, as if they are resisting the torsional by themselves? That may be a conservative assumption but if it works then you're done. If it doesn't work then maybe the assemblies need to be connected in a manner that shares the load? Also, it looks like the points of connection probably need to be checked as well, to avoid localized failure.

It sounds like you've checked these things before so I'd imagine you know much more about it than what I'm able to suggest but those are my thoughts.