Initial cable tension (few quesitons!)

[engABZ]

Hello,

I have some points that I want to verify regarding the initial tension of a cable.
Consider a cable (pinned support at both ends) and want to have as minimum sag as possible.

1) Is that process (cable initial tension) similar to Precast slab Pre-tensioning?
So the cable will have 'built in' tension that will cancel part of the tension that will develop due to applied loads?
(In my case I'm having a udl acting on the cable Parallel to earth).

2) If I'm limited to use Max. strand size of (9/16)inch 1x19 strand. And I am allowed to let the cable have tension due to applied loads close to its breaking strength. How could I determine the initial tension?
I have read about that (initial tension) in (USS Wire Rope Engineering Handbook) but still not certain.

3) Would that Pretension have any effect on the supporting columns?

4) The pretension of the cable, does it have some technical limitations? and how about the cost?

Thanks in advance

 

[csd72]

For most structures the cable can only be pretensioned to a small fraction of its capacity. For small cables I usually ignore this.

Pretension in concrete only works because you have a solid block of concrete to push against.

Just remember that when it comes to cables deflection is your friend.

 

[mijowe]

Here is a link for parking barrier cables, application is different, but the concepts can be used. In garages they do pretension the cables to limit defelctions, set the anchors and to get rid of the innitial sag.

http://pti.mountaininternet.com/reportFiles/28-Technote14.pdf

As indicated above, a little sag is good and realistic, the straighter the cable the larger force on the tops of the columns. If the coluns are not designed for this force they will deflect and add sag to the cable anyhow.

 

[engABZ]

Thanks guys, It is now clear for me.