Torsional capacity of built up light gage members 3

[YukonOne]

I'm trying to calculate the torsional capacity of a 7' long box beam light gage header that has a torque introduced by an eccentric brick veneer. Does it make sense to consider the (2) vertical stud sections and (2) horizontal track sections to be acting as a group as a "closed section" ? (Assuming, of course, that all the componets are connected appropriately)

 

[UcfSE]

Yes. I've done that in the past. You may need stiffeners, vertical or horizontal, where the brick ledge angle connects to the web of the header, if it does.

 

[DaveAtkins]

I have designed the two vertical members (the studs) for the vertical load, and the two horizontal members (the tracks) for the torsion (resolve the torque into a couple, with the equal and opposite forces applied to the tracks). And I recommend a shelf angle that has a vertical leg equal in height to the depth of the box header. If you don't, and you weld the top of the angle leg to the web of the stud, it will probably fail the web in weak axis bending.

DaveAtkins

 

[Deutero]

UcfSE - Can you give me an example of a horzontal stiffener where the brick angle connects to the web? I suppose you could have a horizontal stud member contained within the box at the elevation of the connection. What other idea might you have? As far as a vertical stiffener, I'm imagining that you are referring to member perpendicular to the the angle and also contained within the box. I've never seen this done, nor have I considered this. Seems complicated - Please clarify. I am quite interested in this as many of the buildings I work on are more frequently composed of CFS.

I typically connect the brick/veneer angle to the web with tek screws. I also have had the luxury of having my veneer angle bearing a minimum of 4" on masonry on each side of opening, therefore I've considered my connection to the web only to aid in the resistance of excess deflection and simply to tie the two together. The fact that the angle bears on masonry each side, should eliminate the torsion, should it not?

DaveAtkins - Often the header depth will exceed the angle depth. What would you do in this case? Do you suggest that connecting to the web is not good - unless perhaps stiffened?

Another consideration - (on a slight tangent) For curtain wall situations, I have often used 10-12" track for the vertical side members and multiple 6" horizontal stud members to resist wind.

 

[UcfSE]

Deutero, the tension force of the brick angle pulling on the web of the header may cause too much deformation locally on the web or overstress the web out-of-plane. It won't happen in every case because it depends on the load, of course, and the size of the header to determine just where that brick angle connects. It was indeed complicated but in my case I had a very high load, long span and thus a tall header, and the header alone had to support the gravity as well as wind load. The angle did not bear on anything (horizontal expansion joints as you go up the building side). Vertical stiffeners may be small sections of stud or track or something else as long as it meets with the code requirements for vertical stiffeners. A continuous angle may serve for a horizontal stiffener when properly designed.

The angle bearing on each side wouldn't necessarily eliminate torsion because the support angle will still deflect even if it is sized to resist the entire load. A single angle will twist as well as undergo translation. Where it is fastened to the header, it will pull on the header. Depending on the actual detail you have, the header may have to resist some torsion due to the forced deformation the angle imposes on it.

I've used multiple nested studs and track for overly large headers. Others cases have worked out better with bracing to support headers for wind.

 

[DaveAtkins]

When openings get to the size being described by UcfSE and Deutero, I recommend a hot rolled tube header. I have used these most often with hot rolled tube jambs, but I have on occasion used cold formed steel shoulder studs and king studs with them.

DaveAtkins