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Re: AISC Steel Spec Combine forces question

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but then how is it calculated, is it just the tfb*bf^3/12 * 2?
or is it the tfb*bf * (d/2)^2 ?

or either, depending on direction of load and constraint?

On 12/30/05, Carter, Charlie <carter(--nospam--at)> wrote:

>Jason Christensen wrote:
>I have been reading section H
>of the new steel spec.  This
>section is for designing members
>for combined forces and torsion.
>My question is on section H1 ... it
>reads as follows:
>"... where Iyc is the moment of
>inertia about the y-axis referred
>to the compression flange, in.4 (mm4)."
>My question is with the definition
>of Iyc, specifically the use of the
>word 'referred'.

Iyc is just the weak-axis moment of inertia of the compression flange.

The equation in which it is used in Section H1 is essentially requiring that there be a compression flange. That is, if the ratio of Iyc to Iy is less than 0.1 the compression flange is too small for the behavior to be properly predicted with the provisions in Section  H1. Likewise, if  the ratio of Iyc to Iy is greater than 0.9, the tension flange is too small for Section H1 provisions. In either of these cases, the provisions in Section H2 are more appropriate.

Thanks for pointing out that the "referred to" phrasing is a bit ambiguous.