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Re: seaint Digest for 27 Jul 2004

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Mark,

I think the plan checker is asking you to verify that
the stair framing (stair hangers supporting
intermediate landings and connected to the girder)
won?t put an excessive amount of twist on the girder.
Sometimes stair hangers are 12? to 18? off the
centerline of the beams to which they attach. If the
hanger load is big enough (and the girder is small
enough) this could put some local twisting on the
bottom flange of the beam. 

>From reading your post I think you?re interpreting the
plan checker?s comment as asking you to confirm that
steel beams connecting only on one side of a girder
won?t put excessive torsion on the girder. I think the
plan checker was referring to localized twisting (and
perhaps global torsion) due to eccentric stair hanger
connections to the girder.

HTH,

Cliff Schwinger

--- Mark Gilligan <MarkKGilligan(--nospam--at)compuserve.com>
wrote:

> I have a steel structure with a simply supported
> wide flange girder
> adjacent to a stair opening.  The loads from the
> beams come primarily from
> one side and are transfered using a standard AISC
> shear tab connection. 
> There is metal deck with concrete fill on top of
> this girder.  
> 
> The plan checker is asking me to address the torsion
> on this beam.  My
> practice has been to not explicitly address torsion
> in these cases since
> whatever torsion there may be will be self limiting.
>  While the beam may
> initially apply a torsion to the girder, if the
> girder attempts to continue
> to rotate, the beam to girder connection and the
> beam stiffness will act to
> resist any torsion.  ACI specifically addresses this
> situation in ACI 318
> but I do not believe that AISC does.
> 
> I am trying to figure out a polite answer other than
> "NO", that will not
> take too much time.  Probably the best answer would
> be to reference a
> position by AISC.   Input would be appreciated.
> 
> 
> Mark Gilligan
> 
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