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RE: 70%-30% Bracing Load Distribution

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Rainer,
 
No. The bracing is for cyclic loading (seismic) and the bracing will buckle under compressive loading before the tensile loading is fully mobilized. That means the tension brace needs to be designed for the full load. See AISC Seismic Provisions.
 
Bill
-----Original Message-----
From: raincat1(--nospam--at)aol.com [mailto:raincat1(--nospam--at)aol.com]
Sent: Tuesday, April 26, 2005 9:05 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: 70%-30% Bracing Load Distribution

Bill/ James,
 
Could I arbitrarily assign 70% to the tension brace and 30% to the comp brace? This way my members would be smaller. Or assignment should be based on the stiffness of the braces? 
 
Rainier
-----Original Message-----
From: Scott, William N. <William.Scott(--nospam--at)veco.com>
To: 'seaint(--nospam--at)seaint.org' <seaint(--nospam--at)seaint.org>
Sent: Tue, 26 Apr 2005 08:18:27 -0800
Subject: RE: 70%-30% Bracing Load Distribution

Rainier,
 
You should design the bracing for 100 % tensile capacity assuming buckling of the compression brace.
 
Bill
-----Original Message-----
From: raincat1(--nospam--at)aol.com [mailto:raincat1(--nospam--at)aol.com]
Sent: Tuesday, April 26, 2005 7:09 AM
To: seaint(--nospam--at)seaint.org
Subject: 70%-30% Bracing Load Distribution

In AISC Seismic-02, 13.2c, up to 70% of the lateral seismic force could be resisted by tension braces.
Does this mean that if I have an X-Bracing I could assign one brace to resist 70% (tension) and the other brace to resist 30% (compression)? I will not get the 70-30 distribution by using Staad which will
have 50-50 distribution assuming the brace members are the same.
 
 
Rainier C. Catubig, S.E.
San Diego, California