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RE: Tension rod bracing

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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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