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# RE: Single angle bending member

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Single angle bending member
• From: "Gunnar H. Isleifsson" <ghi(--nospam--at)pc.dk>
• Date: Wed, 22 Nov 2006 21:11:58 +0100

```Scott,

Sorry, my mistake. I assumed, erroneously as it seems, that your design
manual listed the major principal moment of inertia. Not having that
information, does, admittedly, complicate matters a bit.  8-)

Regards,
Gunnar

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: 22 November 2006 18:35
To: seaint(--nospam--at)seaint.org
Subject: RE: Single angle bending member

Gunnar,

There is a slight problem, regardless of whether the equations are valid or
not.  Assuming that one only knows Ix and Iy and A, then you essentially
will have one equation to solve two unknowns (Iz and Iw).  :-)

The second equation does help Joe as the AISC manual does provide rz.  So,
using that second equation, he can now determine Iz.

Regards,

Scott

On Wed, 22 Nov 2006, Gunnar H. Isleifsson wrote:

> Hi Joe,
>
> I haven't seen the AISC Manual, but the equations below are valid,
> regardless of the shape in question.
>
> If memory serves me correctly, the general formulation is, that the
> sum of moments of inertia, about the major and minor principal axis,
> equals the sum of moments of inertia about any cartesian coordinate
> system, with the same origo, rotated with respect to the principal
coordinate system.
>
> There is an article by Y. Ding and M.K.S. Madugula in the Engineering
> Journal (1st Quarter, 2004) that lists Iz and Iw, for angle sections
> listed in the AISC LRFD Manual (2001).
>
>
> Gunnar
>
>   _____
>
> From: jrgrill(--nospam--at)cableone.net [mailto:jrgrill(--nospam--at)cableone.net]
> Sent: 21 November 2006 23:59
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Single angle bending member
>
>
>
> Thanks Gunnar,
>
> I was actually being a little lazy hoping someone had a list of Iw and Iz.
> The formulas on page 17-42 of the manual would be for an angle
> constructed of plates (no fillets or radius at the toes), so I was
> hoping there was a tabel somewhere that could be had, so itterative
> calculations for a beam would be a bit simplified.
>
> Joe
>
>
>
> On Tue Nov 21 17:41 , 'Gunnar H. Isleifsson' sent:
>
>
>
> You can find Iz and rz from the following equations:
>
> Ix + Iy = Iw + Iz
>
> rz = sqrt(Iz/A)
>
> where
> Ix and Iy are moments of inertia about major and minor geometrical
> axis Iw and Iz are moments of inertia about major and minor principal
> axis
>
> HTH
> Gunnar Hafsteinn Isleifsson
> Denmark
>
>   _____
>
> From: jrgrill(--nospam--at)cableone.net [mailto:jrgrill(--nospam--at)cableone.net]
> Sent: 21 November 2006 23:21
> To: seaint(--nospam--at)seaint.org
> Subject: Single angle bending member
>
>
>
> I am looking at the design of an unequal leg angle in bending using
> the new 13th edition of the AISC manual.  In section F.10 I need
> values for Iz and rz for the unequal leg angle to find Me.  Are these
> values listed somewhere I am not familier with.  I think I can
> calculate it from the diagram on page
> 17-42 but I would rather not make any mistakes.  If I have to is that
> the correct formula (O.k. maybe a dumb question for someone that has
> supposed to be educated).  If someone has a list of the values for
> angles I would love to get a copy, or can anyone tell me where to find the
values.
>
> Thanks,
>
> Joe Grill, PE
>
>
>
>   _____
>
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