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RE: Seismic bracing system- Knee-braced Frames

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         Perhaps a little refinement of the description "knee-bracing" will help you get better answers 
         A knee bracing  seems to means different systems to different persons.
         
         One description would be a system where a rafter is perpendicular to two adjacent columns
         and diagonal members  connect the rafter to the weak axis of the columns. This creates a
         frame (But not a braced frame as defined by the code) and also creates serious
         frowning in high seismic areas (the concern there is the same concern that prohibits
         K bracing, see sections 2213.9.4.2). Not advisable in seismic areas.
 
         This system can be improved by adding (2) column working  in the strong axis.
 
         I hope this helps, it is late here we can continue tomorrow
 
         Francois Rambau
         Star Building Systems
         OKC
 
 
-----Original Message-----
From: EphHirsch(--nospam--at)aol.com [mailto:EphHirsch(--nospam--at)aol.com]
Sent: Wednesday, December 04, 2002 8:16 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Seismic bracing system- Knee-braced Frames

Well, this is a question I've been long delaying to pose to Charlie Carter, so thank you for raising it.  Just where do Knee-braced Frames get defined?  As far as I've been able to determine, there is no specific prohibtion to them, yet there is no category to which they seem to be assigned, nor (code) literature dealing with them.  R=??  Are the ductility requirements and detailing per eccentric braced frames?  If Special Trussed Moment Resisting Frames are allowed (to impose a concentrated force where the bottom chord meets the column) would the same be true for a KBF?   etc., etc. Opinions and guidance welcomed.  Thank you.

Ephraim G. Hirsch, S1200 (CA)