Lateral Bending of Colf formed metal studs Boxed headers

[sponton]

Hi everybody,

I was wondering if anybody can point me in the right direction. I am designing some boxed headers and need them taking some lateral loads due to some rather large openings. The typical software we use is the Clark Dietrich's AISIWIN but it doesn't allow the user to do lateral loads. Another problem is that they don't give enough geometric properties for me to input to and run it with Enercalc [as a custom boxed section], STAAD doesn't do cold formed steel boxed sections and their section wizard doesn't let me do a custom section. So i'm out of options, I've tried looking for tables but I haven't been lucky at all. Anybody can point me to a better software or information so I can wrap this up?

 

[tolchijb]

Box headers are typically toe-to-toe unpunched Cee sections with a track top and bottom. I will design the Cee sections to resist the gravity load and the track sections to resist the lateral load.

 

[sandman21]

AISI S212-07 (2012): North American Standard for Cold-Formed Steel Framing – Header Design. Free @ CFSEI

 

[sponton]

@tolchijb

I mean that makes sense but what guarantees composite action between the tracks and how exactly are they typically attached with the C-sections that allows the load to spread between the tracks. I am a bit preoccupied with the torsion, the headers are going to be supporting a canopy connected via the studs on top of the header with a rod.

Most of the information gives talks only about vertical loads but not in conjunction with lateral. I wouldn't be worried if this wasn't a 25 ft long window. I might as well just go for a Hollow section and save me some grief.

 

[sponton]

@sandman21

I checked out your link, I'm affraid that there isn't really a procedure, or actual formulas for failure in biaxial bending. Unless I do what tolchijb suggested and have them take ea. part of the boxed header a loading condition, but that doesn't guarantee that the section will work as intended unless I do the proper connections.

 

[DaveAtkins]

what guarantees composite action between the tracks

There is no composite action--the two side members ("studs") resist vertical loads, and the top and bottom members ("tracks") resist lateral loads.

If you really want a composite box member, weld the tracks to the studs.

DaveAtkins

 

[KootK]

I mean that makes sense but what guarantees composite action between the tracks and how exactly are they typically attached with the C-sections that allows the load to spread between the tracks. I am a bit preoccupied with the torsion, the headers are going to be supporting a canopy connected via the studs on top of the header with a rod.

Yeah, with the load delivered like this, I'd think that you'd want to deal with all of the lateral load in the top track(s) alone. Combined Mx + My + T in a cold formed header sounds like an intractable nightmare. Especially since your support connections probably won't be great for torsional restraint. That issue is probably common to the HSS as well, though, unless you go steel posts as well.

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.

 

[tolchijb]

I agree with KootK that torsion in CFM header will be a nightmare. At 25' long I would absolutely go to a hot rolled tube spanning between hot rolled columns that I can use to resist the torsion. If there was not a canopy you would have a chance, but with the canopy you are going to work very hard to try to save a couple bucks.

 

[XR250]

Gawd, see if you can convince the EOR (if you are the delegated designer) for some tube steel as previously mentioned. It should have been there originally.
I have done this before by adding a bunch of flatwise tracks and flatwise 12ga studs in addition to the vertical studs.
It is usually possible if there is no brick involved and the deflection limits are L/240.

 

[Stenbrook]

Simpson has a cold formed design program called CFS. It isn't free, but it is pretty useful. It won't solve your problem with torsion on your header either. My rule of thumb is that when you have a header larger than 15 ft a light gauge box header starts to get pretty heavy and it is usually better to just go with a steel tube. In your case, a 25ft opening is quite large (combined with torsion) and I would definitely use a steel tube.

 

[sponton]

@KootK,@Tolchijb

Yeah, I ended up giving up. I went with the HSS, like you guys said, whatever cost in material would have been offset with all the time they would spend putting the header together.

@Stenbrook

I'm going to check the software out, since the Clark western software genuinely confuses me more than it helps me.


Thanks everybody for your advise, btw.