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RE: Increaing double-angle brace compressive strength

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> 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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