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RE: Tension Only Braces Seismic Zone 3

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         The tension only bracing is part of the ordinary brace frame (OBF) with an R of 5.6 and omega of 2.2.
         The provision of chapter 22 shall be applied as required for the steel provisions (LRFD & ASD) 
 
         Francois Rambau
         Star Buildings Systems.
-----Original Message-----
From: Peder Golberg [mailto:peder(--nospam--at)jgpierson.com]
Sent: Wednesday, October 03, 2001 1:59 PM
To: seaint(--nospam--at)seaint.org
Subject: Tension Only Braces Seismic Zone 3

Are tension only braces allowed in Seismic Zone 3 anymore?   I have a large one-story building (covers a swimming pool) in design and the architect wants to have 100% windows on one side.  So far I'm losing the battle to get some wall piers.  The building is too large to assume that rotation of the wood diaphragm distributes forces to end walls (cmu walls).  The architect currently will only except diagonal rods in front of the windows (and states that other engineers, our competitors, wouldn't require anything along this wall - per similar previous projects before 97 code), and is against tube steel bracing (braced frame).   I can't find anything that either allows or prohibits this lateral system per the 97 UBC if we use R=2.8 and Omega = 2.2.   I know that the braced frame sections in the code prohibit tension-only braces but can't find any information on design of rod tension-only bracing.     I also see many issues with connections and transferring the loads from a glu-lam drag strut/collector into the steel rods with the omega factor making the loads very high.  I don't like this current system and am looking for justification to discuss alternate lateral options with the architect.  This architect is a big client of ours.
 
Thanks in advance for any tension-only input and comments.
 
Peder Golberg, P.E., S.E.
Portland, Oregon