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Re: X-braces

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Eric: I just got back from an AISC seminar on stability.   Yura was one of
the speakers and specifically addressed your question.  It is a brace (each
way) - a splice plate at the intersection does not change this.
----- Original Message -----
From: "Eric Ober" <eober(--nospam--at)holbertapple.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Wednesday, November 19, 2003 9:39 AM
Subject: RE: X-braces


If you have X-braced HSS sections, then both members are not continuous
across the intersection.  You may have a knife plate connection at midspan
of one of the diagonals.  To rely on the tension diagonal bracing the
compression diagonal (this is required when the 'cut' HSS is in compression)
there is a point bracing force applied (2% rule, Yura/LRFD 3rd Ed. methods,
or whatever method you feel appropriate) which must be considered.  This
puts the tension diagonal into bending along with the tension already in it.
That may be fine if the brace is sized sufficiently, particularly with HSS
sections.

Eric

-----Original Message-----
From: Aswin Rangaswamy [mailto:aswinpe(--nospam--at)hotmail.com]
Sent: Wednesday, November 19, 2003 11:18 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: X-braces

This topic has been the topic of several search.  Try doing a search on
AISC.org and you will see several papers on it (accesible only for members).

1.  Design of Diagonal Cross bracings by A.Picard and D. Beaulieu:  By
theory and experiment concluded that "the effective length of the
compression diagonal is 0.5 times the diagonal lenght when the diagonals are
continuous and attached at the intersection point"

2. FEMA 356 sec. 5.6.2.3.2 says that the effective length of each brace
shall be taken as 0.5times the total lenght of the brace including gueest
plates for both axes of buckling".

Hope this helps.

-  Aswin
_________________________________
Aswin Rangaswamy, P.E.
Jacobs Facilities Inc. (www.jacobs.com )
Cypress, California

----- Original Message -----
From: "Jason Kilgore" <jkilgore(--nospam--at)leok.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, November 18, 2003 1:06 PM
Subject: X-braces


> This something that I thought I knew, but a computer program is calling me
a
> liar.
>
> I have a single story building with steel concentrically braced frames.
> It's in a low seismic area and I'm using R=3.0, so AISC seismic rules do
not
> apply.  Standard slotted HSS X-brace, centered on work points at top and
> bottom .
>
> Here's my question:  Does the tension member serve to laterally brace the
> compression member?  It obviously does in the plane of the braced bay.  My
> argument is that since the opposite member is in tension, it doesn't allow
> the compression member into out-of-plane first order buckling along its
full
> length.  Instead, the compression brace is forced into second-order
buckling
> with the center of the "X" as the node.
>
> Any comments?
>
> ----
> Jason W. Kilgore
> Project Engineer
> Leigh & O'Kane, L.L.C.
> Kansas City, Missouri
>

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