"Standard" Cold Formed Steel Box Beam? 2

You need to be careful by using the members from the tables which do not tell you anything about the loads and connection details. The structural engineers need to understand the basics, and load path through the member, select the size and detail accordingly.

First; can you imagine there are two members attached each other, and no weld/bolt/bonding connection.

Second: these type of beams are from the material with high strength properties. So welding always is a problem, or difficult.

Third: You need to be careful for the load transfer on the faces of the member since the walls are not thick enough. The same apply at the ends of the beam. You need to think about how you will transfer the loads from the beam to the supporting members. Connection elements
such as punching with screw might be needed, and you will be concentration on the details of the connection.

The limitation in the deflection is mostly a code requirement for industrial/building application. The box member is better selection for the torsional applications in addition to other actions, but you still need to validate that your application is safe, at least meets the code requirements.

Corrosion protection is another issue with uncapped member that you need to take care.

The boxed headers are built from studs. They are typically assembled with a track on the top or bottom. For some ideas on the construction, see SSMAs details at Cold formed steel s commonly connected with screws or welds. Often times, welded and screwed alternatives are provided because some contractors prefer welds and some prefer screws.

Back to back headers can be a better option in some cases as there is more resistance to web crippling and easier to insulate. That being said, I usually specify boxed headers. If the load is not too high, I sometimes just specify a single heavy track.

OP said:

if a boxed header is chosen from the table, does it come "off the truck" pre-manufactured with NO seam welds/cap & screws required to be specified by the EOR

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The built up members come from the originating supplier (Dietrich etc) unassembled. Depending on the market and the specialty contractor:

1) Assembly may occur on site or in a fabrication shop.

2) Assembly details may be provided by the EOR.

3) Assembly details may be delegated to a specialty engineer working in behalf of the light gauge contractor.

That's my understanding at least.

XR250 said:

That being said, I usually specify boxed headers. If the load is not too high,

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Given the advantages that you mentioned did back to back, why do you usually go with box headers? Torsion/LTB? Connections?

XR250 said:

, I sometimes just specify a single heavy track.

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Interesting. Oriented as track or strong axis?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

KootK said:

Given the advantages that you mentioned did back to back, why do you usually go with box headers? Torsion/LTB? Connections?

It really depends on what the metal stud sub wants me to specify. For long spans, the boxed is nice as it has better weak axis strength (if needed)

Quote (XR250)
, I sometimes just specify a single heavy track.

Interesting. Oriented as track or strong axis?

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Usually weak axis but this is more for non-load bearing jobs where i am only supporting wall DL. The other thing I do sometimes if the arch. conditions allow, is to use a single, light track for the head of the opening and then screw a "strongback" stud to the rear of the wall above the dropped ceiling that spans from jamb to jamb. The track then only has to carry out of plane loads. Boxed headers are labor intensive so anything to simplify the job is appreciated by my clients. I think Dietrich still makes a super deep leg track that can be used for a header that sits on top of the wall, legs down.

Torsion in a box beam means a critical seam weld. Welds are to AWS or AISI? Welder qualifications for light gage? etc.
This is generally left up to the EOR to sort out. It can be delegated but it doesn't go away.
So far I've stayed away from all structural welding of light gage.

Thanks all! My hunch was as you describe KootK. XR250, while mine is not a wall header scenario, I do have a potential torsion issue on one of my load cases. I will be using a box beam with tracks on top and bottom and appropriate fasteners specified joining the capping tracks to main strong-axis sections.

Buggar - I've got light torsional loads and aim to resolve the torsional moment into eq and opp weak axis loads at top and bottom of the box beam (resisted by the strong axis of the track shapes). Would you steer clear of that approach for light loads?