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Re: strong axis bending of a bar

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In the LRFD spec, I believe lateral-torsional buckling controls the
design, so lateral support will be a major factor.  Check Appendix F,
there's a table that outlines this for different shapes, including
strong-axis plate bending.  Personally, I feel more comfortable using
LRFD for such cases where the 9th edition is a little fuzzy as to what
to use, since AISC isn't developing any newer design criteria for ASD
(at least, that's how I understand it).  I really hope my comments don't
generate a whole LRFD vs. ASD thread...again.  Good Luck.

Mark Nowmos

John Riley wrote:

> I don't know where you got that formula, but I'll take a shot at
> trying to figure out the appropriate stress within AISC.  The
> allowable bending stress for a plate bent about its strong axis has to
> be found in: Chapter F - Beams and Other Flexural Members. F1 -
> I-shaped members and channels.F2 - weak axis bending.F4 - shear
> stress.F5 - stiffeners.F6 - built-up members.F7 - web-tapered
> members. Clearly none of these sections apply, so it must be: F3-
> Allowable Stress:  Bending of Box Members, Rectangular Tubes and
> Circular Tubes. Possibly AISC considers a plate bent about its strong
> axis as a special case of box or rectangular tube.  Within F3 the
> allowable flexural stress will be either 0.6Fy or 0.66Fy, depending on
> lateral support.__________________
> John P. Riley, PE, SE
> Riley Engineering
> 20 Oakwood Drive, Blue Grass, Iowa 52726
> Tel & Fax:  319-381-3949
> jpriley485(--nospam--at)peoplepc.com
>
>      I think this is an easy one but I haven't found it yet.  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 know that
>      .75Fy is good for the weak axis bending.  Thanks for your
>      help.
>
>      Kenneth S. Peoples, P. E.
>      Lehigh Valley Technical Associates
>      1584 Weaversville Road
>      Northampton, PA 18067-9039
>      ph: 610-262-6345
>      fax: 610-262-8188
>      e-mail: kpeoples(--nospam--at)lvta.net
>