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RE: braced frame - double angles in ETABS

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What version of Etabs?

If you are using the new version 7.+, you probably should use 97 AISC
Seismic Code as your design code rather than the UBC.

Is it X-braced? If so, your unbraced length may utilize the intersection
rather than diagonal distance along the entire brace.

Your stitch plates may be the problem - is Etabs treating each angle as an
individual rather than a double angle? The stitch plates allow you to design
assuming a single member rather than two pieces.

Hope that helps.

-----Original Message-----
From: Gina Gobo [mailto:GoboGT(--nospam--at)]
Sent: Wednesday, January 23, 2002 5:16 PM
To: seaint(--nospam--at)
Subject: braced frame - double angles in ETABS

I have a concentrically braced frame modeled in ETABS. Most of the brace
members are double angles. I have posed this question to ETABS and am
waiting for a response. I thought I would email the server to see if anyone
has any input on this.

My brace members (double angles) are coming back as "too slender" when I
complete a lateral analysis using 97UBC-ASD. When I do a hand calc of the 97
UBC slenderness requirements for Zone 3 and 4, the members are ok. I have
set the unbraced length ratio in ETABs, but cannot seem to get the analysis
to get past the slenderness issue. Can anyone provide some insight on this?


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