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# Question about brace design forces for c

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• To: seaint(--nospam--at)seaint.org
• Subject: Question about brace design forces for c
• From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
• Date: Wed, 24 Sep 2003 11:57:43 -0400

```Cliff,

This is from a rigid body buckling analysis of a straight member pinned at
the bottom and with a horizontal linear spring holding the top plumb.

See Timo's Elastic Stability book for his solution.

I saw Bruce G. Johnston do the analysis once about 30 years ago, and although
I have notes, I don't know if I could follow it thru, let alone find the
notes.

HTH

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Clifford Schwinger wrote:

. > Could someone please explain to me where the
. > rule-of-thumb that column braces be designed for 2% of
. > the column vertical load comes from? (I think in Great
. > Britain there is a code requirement to use a value of
. > 2.5%)

. > If 1:500 out-of-plumbness is allowed, then a brace
. > that's restraining the top of one column and the
. > bottom of another column (which are each kinked 1:500
. > out of plumb in a "V" shape) will have a theoretical
. > brace force of 0.4%.  Assuming that you impose a brace
. > stiffness requirement that restricts brace deformation
. > (and additional associated horizontal column movement
. > at the brace connection) to another 1:1000, you would
. > still only have a theoretical brace force of 0.6%. Is
. > the 2% rule of thumb used to provide a safey factor
. > (of about 3) on the very critical brace member, or to
. > account for other unanticipated lateral deformations
. > at or near the brace connection?  Maybe I just
. > answered my own question, but I'd like to get some
. > opinions on this issue.

. > Also, does anyone know why there are no codified brace
. > force design requirements in U.S. codes and standards?
. > The European codes all seem to provide specific design
. > criteria for braces.

. > Thanks!

. > Cliff Schiwnger

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