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Re: seaint Digest for 27 Jul 2004

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I'm sorry Harold, but I just love this.  The plan checker will not accept
industry practice and long term rules so you have to take time to derive a
thesis statement to show a factor of safety of 32.  This was obviously an
outstanding use of your time and energy to prove the obvious, and was
clearly a critical issue worth delaying the approval of a project. (Heavy
sarcasm for those who did not see it).

Sometimes I wonder if the plan checker thinks "I have always wondered how
the hell this works, Harold seems like a bright guy, let's make him prove it
to me."

I am reminded of a previous comment a few years back.  "I know engineers are
not checking their work, because the calculation pages have a checked by box
and no-one has initialed all the boxes".  The fact that there may be
hundreds of pages of calculations to check, not to mention computer models
and a complete set of drawings to coordinate, but I didn't spend an entire
day initialing the entire set of calculations so it is clear that the work
was not checked.  One has to wonder.



Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message ----- 
From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, July 29, 2004 8:57 AM
Subject: RE: seaint Digest for 27 Jul 2004


> Mark,
> You are correct that ACI does indeed address torsion in R/C spandrel
beams.
> This is because you can often times not avoid torsion and torsion cracking
> in the spandrel beam.  It is a function of the aspect ratio of the
spandrel
> beam, and the fact that it is cast monolithically.
>
> Plan checkers often push us to evaluate load paths and mechanisms that we
> often times ignore, or take for granted.  I had a plan checker have me
> assess the stability of a beam.  He did not accept Yura's 2% approximation
> rule.  So I dusted off my Timoshenko, and showed that the beam was stable
by
> a factor of 32.
>
> Steel design practice has traditionally not checked torsion in spandrel
> beams because (as you pointed out), torsion in a spandrel beam is "self
> limiting".  To address the problem posed by the plan checker, I would
> suggest the following:
> 1.  Wide flange shapes are poor in resisting torsion.  Even if the wide
> flange shape would resist torsion your end connections are probably not
> designed to transfer torsion into the column.
> 2.  I would suggest that you evaluate the shear tab connection.  I would
> suspect that you could assume zero moment at the shear tab connection to
the
> web, you could then calculate the maximum moment at the center of bolts
> connecting the shear tab to the beam.  You should have ample moment
capacity
> at that point and throughout the shear tab.
>
> Ultimately you will show that you have no torsion demand in the spandrel
> girder.
>
> I hope that helps.
>
> Regards,
> Harold Sprague
>
> >From: Mark Gilligan <MarkKGilligan(--nospam--at)compuserve.com>
> >Reply-To: <seaint(--nospam--at)seaint.org>
> >To: "INTERNET:seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org>
> >Subject: seaint Digest for 27 Jul 2004
> >Date: Wed, 28 Jul 2004 03:56:51 -0400
> >
> >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 transferred 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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