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RE: AISC Steel Spec Combine forces question

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I believe that it is the out-of-plane moment of inertia of the compression
flange (i.e. Jason's "second thought").  This is kind of confirmed by a
definition of Iyc in the 2005 Specification commentary in Appendix 6 (page
227 of the PDF file of the commentary that I have but the page number
"printed" on the page in the PDF file is 425).

FWIW, this "term" has been around for awhile.  It is at least present in
the 1999 LRFD spec (and thus the 3rd edition of the LRFD manual).  And the
same definition is used in the 1999 LRFD spec (i.e. the "referred"
definition).  In the 1993 LRFD spec also has the term and it is defined in
the same manner.  It is define, however, in the following manner in the
back of the 2nd Edition manual (in the General Nomenclature at the back of
the manual):

"Iyc = Moment of interia of the compression flange about y axis or if
reverse curvature bending, moment inertia of smaller flangem in^4."

HTH,

Scott
Adrian, MI

On Fri, 30 Dec 2005, Garner, Robert 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.
>
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>
>
> Jason
>
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>
>
>
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