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# Re: AISC Steel Spec Combine forces question

• To: seaint(--nospam--at)seaint.org
• Subject: Re: AISC Steel Spec Combine forces question
• From: refugio rochin <fugeeo(--nospam--at)gmail.com>
• Date: Fri, 30 Dec 2005 11:20:57 -0400

Appears to be a warping torsion consideration, but i am not clear on it.  it's been awhile, and i don't see any exact references to these quotes in my literature.

On 12/30/05, Garner, Robert <rgarner(--nospam--at)moffattnichol.com> wrote:

I had that same question - what does "referred to ............" mean.  Sorry for the non-answer but you're not alone with this question.

Bob Garner

From: Jason Christensen [mailto:jason.christensen(--nospam--at)es2eng.com]
Sent: Thursday, December 29, 2005 3:02 PM
To: seaint(--nospam--at)seaint.org
Subject: AISC Steel Spec Combine forces question

To all,

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:

H1.          DOUBLY AND SINGLY SYMMETRIC MEMBERS SUBJECT TO FLEXURE AND AXIAL FORCE

1.         Doubly and Singly Symmetric Members in Flexure and Compression

The interaction of flexure and compression in doubly symmetric members and singly symmetric members for which 0.1 ≤ (Iyc/Iy ) ≤ 0.9, that are constrained to bend about a geometric axis (x and/or y) shall be limited by Equations H1-1a and H1-1b, 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'.  My first thought was Iy + Ad^2, this cannot be correct in that Iy is taken about the y-axis and transferring it to the compression flange does not make sense if my compression flange is involved in x-axis bending, i.e. transferring a y moment of inertia with an x direction.  My second thought is that Iyc is just the moment of inertia of the compression flange about the y-axis, but I am unsure of this also.  Any thoughts would be appreciated.

Jason

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