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Re: Tension rod bracing

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I think the R factors for such bracing types went down to 3.25 from 5 and I am interested in knowing the rationale behind this move. I have tried finding literature related to work
regarding the behavior of Tension only rod bracings, but they are often dated and from out of the US (Japan and Australia) hence hard to get a hold off.
 
Ganesh

 
On 6/16/06, Syed A Masroor <masroor(--nospam--at)eaworld.com> wrote:
Can Charlie or some one tell us WHY tension only systems are being so
restricted by the new codes? Is it something theoretical or performance
related ? After all, we have lived with them for so long.

S A Masroor

----- Original Message -----
From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com >
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, June 15, 2006 11:26 PM
Subject: RE: Tension rod bracing


> What you stated is true.   I was presuming that Drew was wanting to remove
> an SCBF and replacing it with a tension only OCBF.  But tension only
OCBF's
> are are very restricted more by the IBC and ASCE 7 as opposed to AISC.
The
> original concept (crafted in the secret code development room on a far
away
> planet) was to just allow tension only OCBF's for PEMB's only for
buildings.
>
> Obviously, there are more variables that need attention.  But the
> fundamental question of using a tension only OCBF is that they are allowed
> under some limited circumstances.  Some of the best performing structures
> around are the tension only braced systems used for elevated water towers.
> Now these are important structures, and they have a good track record.
> Granted they do some special features, but the basic concept is still a
> tension only OCBF.  By the way, we allow tension only OCBF's if they are
> categorzed as nonbuilding structures.
>
> Regards,
> Harold Sprague
>
>
> >From: "Haan, Scott M POA" <Scott.M.Haan(--nospam--at)poa02.usace.army.mil>
> >Reply-To: < seaint(--nospam--at)seaint.org>
> >To: <seaint(--nospam--at)seaint.org>
> >Subject: RE: Tension rod bracing
> >Date: Thu, 15 Jun 2006 07:12:48 -0800
> >
> >You cannot have a specially concentric braced frame with tension only
> >bracing
> >without any compression bracing per AISC341-02 13.2c.  The exception to
the
> >30% to 70% tension brace rule says you need to have some compression
braces
> >designed for special load combinations in any line of bracing if you
> >violate
> >the 70% amount of tension braces.
> >
> >If you are going to have tension for a grid line they need to be designed
> >for
> >special load combinations with an ordinary braced frame R.
> >
> >-----Original Message-----
> >From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com]
> >Sent: Wednesday, June 14, 2006 4:21 PM
> >To: seaint(--nospam--at)seaint.org
> >Subject: RE: Tension rod bracing
> >
> >As with everything else.... it depends.  Are you using ASCE 7 or IBC, and
> >which edition?
> >
> >The 2002 AISC Seismic Provisions do not preclude tension rod bracing.
What
> >will limit the applicability is the ASCE 7 or IBC.  The biggest variables
> >are:
> >A.  Seismic Design Category.  Since you are using a SCBF, I would presume
> >that you are in SDC D, E or F.
> >B.  Height
> >
> >Look at ASCE 7-05 Table 12.2-1.
> >
> >Regards,
> >Harold Sprague
> >
> >
> >
> >
> >
> > >From: Drew Morris <dmorris(--nospam--at)bbfm.com>
> > >Reply-To: <seaint(--nospam--at)seaint.org>
> > >To: SEAINT < seaint(--nospam--at)seaint.org>
> > >Subject: Tension rod bracing
> > >Date: Tue, 13 Jun 2006 09:18:26 -0800
> > >
> > >Under the 2002 AISC Seismic Provisions is tension rod bracing
prohibited?
> > >We have a case where the building will be designed as a special
> > >concentric braced frame, but the architect is objecting to those braces
> > >that will be in front of large windows.  Can tension rod bracing be
> > >used for these locations?  The building is a 2 story structure and the
> > >braces will be on both levels.
> > >
> >
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