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[SEAOC] Re: Special Concentrically Braced Frames

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Carl:

The idea is that under real earthquake loading, the brace is expected
to buckle.  With that as a given, the "exception" is supposed to 
provide a connection that will allow the brace to buckle out of the 
plane of the gusset plate, forming hinges within the gusset, but not 
destroying the weldments at the connection.  The setback of 2t is 
supposed to provide a clear hinging region within the gusset plate.  

> From:          CarlS95(--nospam--at)aol.com
> Date:          Sun, 17 Mar 1996 22:57:54 -0500
> To:            seaoc(--nospam--at)seaoc.org
> Subject:       Special Concentrically Braced Frames

> Is the ListServer not reaching me or is it just that everybody has been real
> quiet the last few days?
> 
> Here's a trivia question:  In UBC Section 2211.9.3.3, gusset plates at the
> ends of special braced frames are required to be stronger in flexure than the
> brace.  An exception is "where the out-of-plane buckling strength of the
> brace is less than the in-plane buckling strength and the brace terminates on
> a single gusset plate connection with a setback of two times the gusset
> thickness from a line about which the gusset plate may bend unrestrained by
> the column or beams joints" and so on.  What does this exception mean and
> why?  Specifically, what is the purpose of the setback of two times the
> gusset thickness and is this a minimum or maximum setback?  And am I supposed
> to understand this? (My apologies to whoever, or whomever,  wrote this
> section of the code--I did go to school and studied real hard, but I still
> don't understand. English grammar wasn't my best subject.)
> 
> Thanks.  Carl Sramek
> 

Stephen K. Harris
EQE International
44 Montgomery St, Suite 3200
San Francisco, CA 94131
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