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Re: 70%-30% Bracing Load Distribution

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Be careful of arbitrary assignments of loads.  Remember that the structure doesn't know what you assumed. It will behave according to the laws of Nature based on stiffness and load capacity.  Your assumptions should account for the important factors.
Bill Cain, SE
Berkeley CA 
-----Original Message-----
From: raincat1(--nospam--at)
To: seaint(--nospam--at)
Sent: Tue, 26 Apr 2005 13:05:15 -0400
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? 
-----Original Message-----
From: Scott, William N. <William.Scott(--nospam--at)>
To: 'seaint(--nospam--at)' <seaint(--nospam--at)>
Sent: Tue, 26 Apr 2005 08:18:27 -0800
Subject: RE: 70%-30% Bracing Load Distribution

You should design the bracing for 100 % tensile capacity assuming buckling of the compression brace.
-----Original Message-----
From: raincat1(--nospam--at) [mailto:raincat1(--nospam--at)]
Sent: Tuesday, April 26, 2005 7:09 AM
To: seaint(--nospam--at)
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