CFS Box header design resources

[StrEng007]

It's amazing how little information there is on this subject. The best resources I've been able to come up with are CFSEI technical note on header design. It simply tells the user to consider a box header to be double the capacity of a single stud member for flexure, shear, and web crippling. It doesn't address anything to do with how to weld or assemble the box header.

Maybe it's not even required? If the capacity is double the single member, there is no reliance on shear flow to create a composite section for bending about the strong axis, right?



Even more annoying is SSMA's table for box headers. It provides allowable uniformly distributed loads but offers no comment on how to assemble the section. Additionally, it states in its footnotes that all beams are considered to be adequately braced? From my point of view, most boxed headers that have cripple studs on top are fully unbraced, so I don't know how much help this document actually helps.




I would appreciate any resources outside of the two referenced and the AISI document.

 

[RWW0002]

If the members are the same size, and oriented as you have shown, there is no shear flow between them for vertical load only and really no composite action. The connections would be nominal outside of thinking through lateral bracing of the individual sections. You are not showing it, but typically there is also at least one track member top and bottom. The track members can provide some resistance to out of plane loading so the vertically oriented members can be designed to resist vertical loads only.

 

[Celt83]

For the fastener design refer to AISI S100-16-2020 Chapter I and the associated Commentary Chapter

https://www.buildusingsteel.org/wp-content/uploads/2023/06/AISI-S100-16-2020-wS3-22.pdf

 

[Celt83]

Specifically for Headers Reference AISI S240 which incorporated the older ASIS S212. If I recall correctly the design provisions in S240 are based on testing and require the specific assemblies from chapter C of that standard, e.g. the box header requires the track lips wrapping onto the C/S webs, so for a cripple wall above you'd need an additional track to receive the cripples.