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Re: STILL MORE on Angle Bending

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--- Bill Polhemus <bpolhem(--nospam--at)swbell.net> wrote:
> 
> Now, I have another question.
> 
> Equation (5-5) on page 6-285 of the 2nd Ed. LRFD manual calls for bending
> coefficient Cb; however nowhere in section 5.3. where this equation appears
> is
> Cb defined. In the entire chapter it is only defined in one place, in fact:
> Section 5.2.2. which is under the heading "Bending about Geometric Axes".
> There
> Cb is given as a definition under Equation (5-4).
> 
> From context I can't tell right off if the Cb definition in Section 5.2.2. is
> ALSO the definition to be used in equation (5-5). Can anyone confirm or deny
> this for me? Charlie, maybe?
> 

Eq. F1-3 on p. 6-53 provides the same equation for the "bending coefficient". 
My understanding is that this equation is dependent on the the "shape" of the
moment diagram, not on the cross-section of steel to which it is applied.  In
defense of this position, the 1996 Cold-Formed Steel Design Manual states the
same equation on the top of page V-48 for use in the calculation of "lateral
buckling strength" of "singly-, doubly-, and point-symmetric sections".

Obviously, there are caveats for the use of this equation (cantilevers, sudden
changes in moment diagram, evaluation accross moment and curvature inflection
points, etc.).

If I am mistaken about this, someone please correct me (though I almost always
use Cb = 1.0).

Keith Fix, PE
Cromwell Architects Engineers

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