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RE: strong axis bending of a bar

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Title: RE: strong axis bending of a bar

>I have written in my AISC 9th edition that the allowable
>bending stress of a plate bent about its strong axis is
>Fb = 10,000/ (Ld/(t cubed)) <.66Fy.  Anybody know
>where I got this?  Is it correct?  Is it in the AISC spec?

I'm not sure where you got this, but be careful with this and all the other "magic" formulas that have been suggested.

For any general bending member, the controlling strength limit state may be yielding, lateral-torsional buckling (LTB) and local buckling (shear too, but I'm concentrating on flexure here). For a very specific member and span characteristic, like a W-shape that is also braced (no LTB) and compact (no local buckling), we can have a simple and single formula for the flexural strength: 0.9FyZx in LRFD or 0.66FySx in ASD. But a plate in strong-axis bending isn't quite so simple.

From LRFD Specification Appendix F, either flexural yielding or LTB will control. Additionally, the LTB can occur in the inelastic range or in the elastic range, depending upon the span slenderness parameter Lb/ry. Note that the effects of local buckling need not be considered for this case because they are essentially indistinguishable from those for LTB.

The corresponding equations for these checks are a bit too much to type into a text-based email. But if you're interested and reply to me privately with your fax number, I'd be happy to fax you the solution for the full range of behavior on Monday.

Charlie