Wide Flange Loaded Across the Flanges

[ringerA]

Could someone please run through the general calcs for the loading case of a wide flange on its side with the load being applied across its flanges? The beams are being used as saw horses and I need to determine a rough rated capacity.

 

[14159]

Please clarify. Your description is not clear enough to allow intelligent comments.

Are you concerned with weak-axis bending of the WF beam or concentrated load capacity (like buckling or crippling)?

My best guess from your description is that you have a concentrated load that's being applied transverse to a flange that's putting the flange in compression. In this case, you'd be concerned with yielding, local buckling, and lateral buckling of the flange. Is this your situation?

DBD

 

[vooter]

You're using structural steel beams for saw horses? You must be as strong as Anthony Clark to move 'em around!

 

[ringerA]

Yes DBDavis,
I am concerned with the concentrated load capacity. Please elaborate on the most crucial calcs concerned with this application.

 

[14159]

I can think of a few applicable limit states. First, I should issue a disclaimer. I am not 100% sure what you're doing, but this is my best interpretation. I also assume that you're using typical W-shapes, not a built-up slender member with really wide, skinny flanges. I also assume that you're not putting humongous loads on there.

1. Flange yielding limit state, similar to the web yielding limit state given in Chapter F of the 3rd Edition LRFD Spec. You just don't have a k part of this equation to help increase your bearing length. tw would be replaced by tf in your case. N would be whatever length of bearing you have for your condition.

2. Flange crippling, similar to web crippling in Chapter K: I have no clue how to check this and think that check #3 should cover this.

3. Lateral buckling. You also have to invent this calculation. I think your KL/r ratio is small, but might not be, depending on the slenderness of your flanges. Use K=2 and L=bf/2, r=0.29tf. Use Table 3-36 or 3-50 as applicable to come up with your stress. The A is the part you must invent. In reality this is a plate buckling problem, but we don't wanna get into that. You could define a little length of your flange as the column width, call it w. Then A=tf*s and phiPn=0.85*Fcr*A. Hopefully this is about 18x bigger than your load....

4. While not definitive, I'd make sure that my bf/2tf ratio was stocky. I know of no other way than to make sure it's less than lamba_p given in the Chapter B table.

I hope this helps.
DBD

 

[UcfSE]

Will this involve a moving concentrated load? If necessary can you reinforce the flanges with stiffeners?

You need to check local instability of your section with the AISC limits and adjust the section properties as necessary. With weak-axis bending of a wide flange lateral-torsional buckling is not a concern. Mn=FySx or Mp=FyZx

From here you may or may not need to reinforce your flanges in the vicinity of the concentrated load, depending on the size of the flanges and the load of course. The closest design criteria I can find for a compressive force on your flange causing instability is K1.5 in the AISC 3rd LRFD. If you check using this equation and have a very large factor of safety, say 10 for instance, you're probably all right but who really knows. It may prove easiest to just reinforce the flanges and be done with it, which is probably a good idea if you are looking at very heavy loads.