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Re: AISC Seismic PRovisions for SCBFs

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John Conner has raised a good question, and Ben Yousefi and Michael Cochran 
have provided him with valuable advice.  However, I believe a few points 
about SCBF design need clarification:

I    The "R" factor for SCBFs corresponds to a brace yielding mechanism, 
not to collector failure.  Analysis may indicate that not every connection 
must resist brace yielding when the yield mechanism forms.

II   The brace-to-brace connection must also be designed for these forces.

III  To limit the connection demand there are a few things that can be done 
with the overall frame design to permit using a smaller brace:
  A  Lower-strength steel should be considered for slender braces.
  B  Pipe sections which have less severe width-to-thickness limits, can be 
  C  Flat-wall width not overall width, should be used when following the 
AISC Specifications.
  D  Full flexural and axial continuity through the brace-to-brace 
connection can be provided; this will reduce the effective length to below 
the half length.  Be aware that for out-of-plane buckling this may induce 
significant torsion in the tension brace.
  E  If possible, the ends of the brace should be fixed.  If this can't be 
done, measure the brace length from the line of restraint at the hinge 
zone, not from the column centerline.

John, if any of this is unclear or if you would like references for the 
above, please feel free to contact me directly.  Good luck,


Rafael Sabelli