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RE: cable x-bracing

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Mark,

The venerable old tension only X braced frame is like the old soldier.  It
hasn't been killed outright, but for good or bad it has slowly faded away in
the UBC.  The X braced frame is still defined in the glossary, but I believe
that is its only mention.  The only way that you can use tension only X
braced frames within the good graces of the various codes, is through the
back doors created by exceptions for the prefab metal building industry.
Even within the exceptions, the X brace is not specifically mentioned except
in the glossary, and the tension only X braced frame is not mentioned at
all. 

The bottom line is that if you use tension only X braced frames, you are on
your own.  And with cables, you need to be looking at the ASCE 17-95.  Aside
from the obvious nonlinear dynamic analysis (I am being a bit facetious),
you should preload the cables.  

Preloading the cables is the only way you can be assured of a reasonable,
predictable lateral drift.  The preload in the cables is not easy.  Because
of the shrinking and swelling of the wood, you should preload the cables to
a point that the compression forces in the wood can resist, and that the
shrinkage can maintain.  Then there is the issue of creep in the wood, .....
etc.

This little project would make a great doctoral thesis.

Regards,
Harold Sprague


> -----Original Message-----
> From:	Mark D. Baker [SMTP:shake4bake(--nospam--at)earthlink.net]
> Sent:	Tuesday, July 25, 2000 6:13 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	cable x-bracing
> 
> I would like to use aircraft cable for vertical cross bracing  to take
> seismic loads at the outermost edge of a residential deck.
>  
> The deck is supported at this edge by a 6x12 beam carried by 6x6 posts.
> The x-bracing would of course occur between the 6x6 posts.
>  
> Any comments on how the 97 code will impact this design? 
>  
> Mark


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