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RE: Increaing double-angle brace compressive strength

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I cannot see how bolting in case B is the same as Case
A. In case B bolting of the channel will require the
use of clip angles.

I have one other idea. Insert the web of a WT section
between the "back to back" segment of the angles such
that the flange of the WT makes the whole section in
the form of an I-section. You can choose a WT (and, if
necessary, bolt a flat plate on the outstanding legs
of the double angles) to get the required ry.

Rajendran


--- Dave Evans <DEvans(--nospam--at)tnh-inc.com> wrote:
> > How do you bolt in case B?
> Same way as in A...between the existing angles.
> 
> > 
> > Are the long legs back to back?
> Yes.
> 
>  
> > Can you weld instead of bolt?
> Strong preference to bolt.  These are on an antenna
> structure a 
> couple hundred feet in the air.
>  
> 
> > You are trying to reduce kl/r right? r=sqrt(I/A)
> Need to carefully
> > choose the orientation of the new steel to
> maximize the I/A ratio.
> > 
> > Can you decrease K by doing something with the end
> connections to
> > create a fixity?
> No.
> 
>  
> > Are you treating these as individual angles? Or
> are they acting
> > together Via a stitch plate? Might be
> easier/cheaper to simply replace
> > the braces or install them as X-braces so they
> only need to act as
> > tension only braces.
> They're stitched together.  Replacing is not an
> option. Tension-only 
> is not an option.
> 
> 
> > Is it out of plane buckling or in plane buckling?
> (this gets back to
> > whether the long legs are back to back.)
> OOP with LLBB.
> 
> > Just some thoughts,
> > -gerard
> > Santa Clara, CA
> > 
> > -----Original Message-----
> > From: Dave Evans [mailto:DEvans(--nospam--at)tnh-inc.com] 
> > Sent: Thursday, August 01, 2002 7:57 PM
> > To: seaint(--nospam--at)seaint.org
> > Subject: Increaing double-angle brace compressive
> strength
> > 
> > We need to increase the compressive strength of
> some double 
> > angle braces. Y-Y axis buckling is the problem.
> Our first thought was
> > to bolt a channel to each one so that the channel
> web is in contact
> > with the angle outstanding legs and the angle
> outstanding legs nestle
> > between the channel flanges thus (hope this art
> comes thru):
> > ------------------ |  ----   ----   |
> >        | |
> >        | |
> > 
> > Call this Case A.  It is easy to analyze using the
> "lean-on" bracing
> > concept.
> > 
> > Where this arrangement is physically impossible
> because of 
> > attachments to the brace, it would be possible to
> invert the channel
> > and bolt it to the back-to-back legs thus:
> > 
> >    ----   ----   
> >        | |
> > |      | |        |
> > ------------------
> > 
> > Call this Case B.
> > 
> > I like Case A much better than B, mostly because
> in Case A, the 
> > shear centers of the channel and double angles are
> relatively close to
> > each other.   In Case B, they are quite distant. 
> The problem is
> > figuring out whether or not there is a significant
> difference in the
> > effect of the reinforcement.  
> > 
> > I've considered the
> column-constrained-to-buckle-about-a-fixed-axis
> > concept for Case B, but that's not completely
> accurate.  Might be good
> > enough, though.  Any comments or other ideas on
> how to approach Case B
> > would be appreciated.
> > 
> > Dave Evans, P.E.
> > TNH, Inc.
> > 
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