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# RE: Cb for Channels Bent About Major Axis (AISC 360-10 Section F2)

• To: seaint-seaosc(--nospam--at)mail-list.com
• Subject: RE: Cb for Channels Bent About Major Axis (AISC 360-10 Section F2)
• From: "Polhemus, William" <wpolhemus(--nospam--at)craworld.com>
• Date: Fri, 19 Jul 2013 17:34:10 +0000
• Accept-language: en-US
• List-subscribe: <mailto:SEAINT-SEAOSC-on@mail-list.com>

```Lloyd:

Perhaps it does.

However:

The 9th Ed. Was published in 1989. That's 24 years ago.

I don't even know where my copy of that is - in some box somewhere in my
garage, I guess.

There has been a large body of research since then, filling in blanks and
helping us to design steel more efficiently and effectively.

While the equation you reference may still be valid, I suspect it has been
superseded by newer research that has since been incorporated in the AISC
Specification.

That's what I was looking for.

-----Original Message-----
From: seaint-seaosc(--nospam--at)mail-list.com [mailto:seaint-seaosc(--nospam--at)mail-list.com] On
Behalf Of Lloyd Pack Sent: Friday, July 19, 2013 12:27 PM
To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Cb for Channels Bent About Major Axis (AISC
360-10 Section F2)

Hello Bill,

I will attempt to help.

In the AISC 9th Ed of the Manual of Steel Construction (ASD) There is a
says to use the following eq. for allowable stress:

Fb = (12 x 10^3 x Cb)/(Ld/Af)  <= 0.6Fy

Where Cb is equal to 1.75 + 1.05(M1/M2) +0.3(M1/M2)^2 below this equation
is a paragraph that mentions reverse curvature bending and what affect that
will have on the sign of the M1/M2 ratio.

In Design of Steel Structures by Gaylord, Gaylord and Stallmeyer they've
got a more developed equation for when the moment diagram within the
unbraced length isn't a straight line.  It looks like this:

Cb = (12.5Mmax) / (2.5Mmax + 3Ma + 4Mb + 3Mc)

Truncated 1058 characters in the previous message to save energy.

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