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RE: Large Bay 'X' Bracing

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Assuming the 21 kips is the brace tension load (and not the horizontal component) you should be able to handle that load with a 50 ksi 1-1/8" diameter or larger rod.  A rod that size should connect into the framing members with a clevis (note not every clevis is designed the same so check its capacity as well).
 
The L/r limit is very similar in both the 9th Edition and the 13th Edition (2005 spec).  For both specs the L/r limit is a "preferred" not "required" limit... the wording in the 9th edition is "For members whose design is based on tensile force, the slenderness ratio L/r *preferably* should not exceed 300.  The above limitation does not apply to rods in tension."  Emphasis on preferably added by myself... also per this note rods in tension are even excluded from the preference.  The 2005 spec has a very similarly worded user note in D1.
 
Hope this helps,
Greg

 

From: Rich Lewis [mailto:seaint04(--nospam--at)lewisengineering.com]
Sent: Tuesday, May 29, 2007 6:01 PM
To: seaint(--nospam--at)seaint.org
Subject: Large Bay 'X' Bracing

I have a warehouse condition of a ‘X’ braced bay that is 31 feet high and 42 feet wide.  The diagonal length is over 51 feet.   I’m wondering if I should try to use the bracing as one large bay, or add a wind column in the middle and have two smaller bays.  The bracing is tension only for wind loads.  The load in the diagonal is about 21 kips.  What makes me most uneasy is the slenderness ratio of the brace.  If I try to limit the L/r ratio of the out of plane axis to 300 then I get extremely large angles.  If I ad a column I add almost 50% more bracing length, plus column and footing.

 

Thanks for your insight.

 

Rich