From: Rafael Sabelli <sabelli(--nospam--at)dasse.com>
Date: Mon, 12 Apr 1999 10:07:45 -0700
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
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,