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Re: cable x-bracing?

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Karen,

        I have had some involvement with the use of guyed structures, primarily tall guyed stacks.  Following are some points that you may find interesting or may want to research in more detail.

        The properties of "cable" vary considerably depending on manufacturer, configuration (number of wires, etc.) whether it's wire core or fibre core, and with the degree of stretching applied.  It's imperative that you get the supplier's (or manufacturer's) catalogue for complete information relating to the type of "cable" you want to use.  Flexible "wire rope" will be much different from galvanized "bridge strand".

        The modulus of elasticity ,E, may vary from less than 10,000,000 p.s.i. to more than 20,000,000 p.s.i.  Typical examples for galvanized strand are 14,000,000 p.s.i. for unstretched and 18,000,000 p.s.i. for stretched wire core strand.

        There was a thread on this list several months ago (perhaps a year or more) dealing with flat bar bracing.  Some of the comments made at that time might be applicable to the use of "cable bracing".  I would suggest that you look that up.

        Whether you use flat bars, rods, or cable bracing it would be desirable to have it tensioned (at least moderately) on installation.  You would design for tension only bracing since cable bracing can only take "effective compression" up to the limit of the pretension force installed.  Cable bracing would work better for resisting wind loading than for resisting seismic loading due to the greater magnitude and frequency of stress reversals for seismic loading.  Shrinkage of the wood will be a consideration.

        By the way, I admire your imagination in attempting, or considering, something unusual; that's what real engineering is all about.

Regards,

H. Daryl Richardson

"Nels Roselund, SE" wrote:

Karen, Isn't cable quite a bit more flexible than solid steel?  It seems that sizing would need to be based on displacement control rather than strength -- especially if you are dealing with a rigid diaphragm.  Cable assemblies are unconventional in residential construction -- it may be hard to find a residential contractor who is familiar enough with it, and you may need to have more-than-ordinary involvement in the construction process to be sure that the frame is properly built. Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net