Define initial tension of wire rope bracing members?

[drile007]

Hello,

I'm wondering how to correctly design wire rope bracing? How to define initial (pre)tension, should I include/neglect self weight?
Any comments/guidance are highly appreciated.

Thank you in advance

 

[Lomarandil]

It depends on your system.

If you're using a small diameter wire rope with high installation tension, or the bracing is near vertical, you may be able to neglect self weight and sag.

If you're dealing with larger diameter wire rope, low installation tension, or bracing geometry that is significantly horizontal, self weight and sag become pretty important.

If you are relying on the wire rope bracing to provide some sort of stiffness to your system, I would almost always account for self weight and sag.

Finally, in most cases it is more practical to define a sag requirement for installation than a tension requirement. Sag is easier to measure.

 

[rb1957]

I'd've thought "turn of nut" would give you good control on cable tension.

Cable tension should be sufficient to overcome anticipated compression loads or some stiffness criteria (deflection of the head of the mast ?).

I'd've thought weight was always included (sure, sometimes it may be small compared to other loads; sure, someone with experience can say "acceptable by review").

another day in paradise, or is paradise one day closer ?

 

[dhengr]

Drile007:
Wire rope/cable has two forms of stretch, namely elastic stretch and mechanical stretch. The latter is a function of the lay of the wire rope and its manufacturing methods. Wire rope generally has too much stretch/elongation per unit load to be used effectively for bracing in buildings, because you can’t tolerate the P/Delta movement of the structure or its surface finishes and the like can’t tolerate this movement. Thus, it is generally better to use round or rectangular solid steel bars, or angles, channels and the like for diag. bracing in bldgs. Cable works fine for tethering or bracing something like a crane boom or any other structure or machine which can work around the cable stretch under loading.

 

[drile007]

Thanks everyone for the valuable input.

Can you recommend me some design/installation guides/recommendations where I can find allowable sag/recommended initial tension?

Thank you in advance