Re: Torsion in wide flange shapes

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Torsion in wide flange shapes
• From: Rick.Drake(--nospam--at)Fluor.com
• Date: Tue, 8 Jan 2002 12:40:12 -0800
• Cc: seaint(--nospam--at)seaint.org
```Charlie Carter et al did a great job with the AISC Design Guide 9.  Of
particular value are the graphical representations of the differential
equations involved in the solution.

For background theory, Salmon & Johnson have an excellent discussion on
torsional stresses in open shapes, including many helpful pictures and
examples showing all the normal and shear forces in the flanges and webs.

Rick Drake, SE
Fluor Daniel, Aliso Viejo, CA

******************************

Scott Maxwell
<smaxwell@engin.      To:     seaint(--nospam--at)seaint.org
umich.edu>
01/08/02 12:27        cc:
PM
Please respond        Subject:     Re: Torsion in wide flange shapes.
to seaint
.

Mark:

This can get a little complicated.  If you are dealing with a closed shape
(i.e. a tube) then torion can be a relatively simple thing to deal with.
In that case you will only have to deal with torion stress that are in the
form of shear stresses.

Open shapes, however, are a whole different ball game.  Torsion stresses
in open shapes (i.e. a wide flange section) will produce both shear
stresses and normal (axial/bending) stresses.  When dealing with open
shapes, the torion can be "broken down" into St. Venant torsion (pure
shear stresses) and Warping torsion (both shear stresses and axial/bending
stresses).  The St. Venant torion is basically similar to the torsion in a
closed shape.  The warping torions is something that only occurs in open
shapes.  It is actually somewhat in intuitive if you really think about
it.  Imagine in your mind an I-beam twisting...you should be able to see
the flanges warping as it is twisted...and it should be somewhat apparent
that there will be some normal stresses introduced due to the deformation
"shape" of the I-beam.

The end result is that the whole torsion issue is rather complicated for
open shapes (I only got my introduction to it in a PhD level
course...which was VERY helpful).  Thus, I would suggest that you wait for
the AISC Design Guide to arrive if you can.  It will do a good job of
helping you deal with the complicated issue.  I believe that Design Guide
is based off of a publication that Bethlehem Steel (?) produced on
designing for torsion, but I think AISC has added much more explanations
that the Bethlehem Steel publication (which just confused me...especially
since I had not taken my course that contained torsion yet).

HTH,

Scott
Ypsilanti, MI

On Tue, 8 Jan 2002, Harper, Mark wrote:

> I have a condition where there is some torsional force introduced in the
> column due to the geometry of the precast connection.  My question is
> this, What unity check do I have to make if any?  Generally I would make
> a combined bending  and torsional stress  check but I am not sure about
> axial load and torsion.  Would it be fa/Fa + Tv/Fv <=1  Or maybe fa/Fa +
> ( Torsional bending stress/Fb)<=1 ???
> I have ordered the AISC Steel design guide 9 on torsion, but would
> appreciate any input.
> Thanks,
> Mark
>
> Mark Harper PE, SE
> HDR INC.
> 201 South Lake Ave. #705
> mharper(--nospam--at)hdrinc.com
> Phone: (626) 584-1706
> Fax: (626) 584-1750
>
>
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