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RE: steel brace

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Charlie & Scott, I wish I could change the bracing system but the architect
has left me with limited options.
Scott is correct in explaining the system that I am proposing here. (a 1
brace chevron)
Why is this a bad system?
It seems to me like the brace system could be considered as both a
concentric brace and a moment frame since the brace is putting the beam into
bending?
Maybe it would behave similarly to a knee brace type of system?
What to you guys think?

Greg Meyer


-----Original Message-----
From: Carter, Charlie [mailto:carter(--nospam--at)aisc.org]
Sent: Wednesday, July 24, 2002 8:02 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: steel brace


>Yes, for the descriptions provided it
>appears to be what you descrbe (i.e.
>half of a "chevron" type brace).

That kind of detail could get ugly quick in my opinion.

For SCBF, we have requirements that make V and inverted V braces robust to
minimize the potential for losing a diagonal (which makes a nice concentric
system eccentric). Then we have requirements for V and inverted V systems to
ensure that, if a diagonal is lost, the beam can carry gravity load and the
system does not destabilize. Seems like this configuration intentionally
starts at the point we have a bunch of provisions in there to avoid.

Perhaps it could be treated as an EBF, but there are aspect ratios for links
that must be satisfied. Also, a link adjacent to the column makes for a
system that places a higher inelastic rotation demand on the beam to column
moment connection than for the same interstory drift on a moment frame.
Again there are specific provisions to keep out of trouble. So you wind up
putting the link between the braces or really beefing up the moment
connection.

Can you configure the system another way? That may be the best solution (and
the simplest).

Charlie








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