Calculating amount of sag and tension for 1/8 steel cable

[Cjbsurf]

Thanks for reading, hopefully I am posting my first question in the correct area of the forum!

I will list as many details as I have in hopes that someone will know how to calculate the amount of sag I will have and tension/force there will be.
I am suspending a 1/8 steel cable horizontally (like a zipline) between two concrete pillars that are 32' across and will sit at 16ft high. I will be hanging stationary objects 16' centered across this 32' cable, the 14 objects weigh 3.5 ounces each so combined they will be just over 3 pounds total hanging from the cable. The cable has a breakstrength of 2,000lbs.

With this information I am in need of finding out how much force or tension I am causing between the two pillars I am suspending the cable from and what the sag in the cable will be. Thanks in advance for any information or help you can offer, it is appreciated!

 

[anorlunda]

https://www.spaceagecontrol.com/calccabl.htm

You need a catenary calculator. There are many online. This is the first one Google found for me.

 

[Nidum]

Depends largely on how much you pre tension the wire . What do you intend to do about this ?

 

[sophiecentaur]

how much you pre tension the wire

Surely there would be a length / tension adjustment to allow for the bends in the wire to be taken out, after the wire is installed and loaded.

 

[Nidum]

Doesn't matter that much when the wire is actually tensioned - what matters is that it is a user controlled input ?

 

[sophiecentaur]

a user controlled input

Meaning a design variable?

 

[Cjbsurf]

Doesn't matter that much when the wire is actually tensioned - what matters is that it is a user controlled input ?

https://www.spaceagecontrol.com/calccabl.htm

You need a catenary calculator. There are

Depends largely on how much you pre tension the wire . What do you intend to do about this ?

Depends largely on how much you pre tension the wire . What do you intend to do about this ?

I have not calculated the pretension. I have only gathered the information I listed along with the weight of the 32' 1/8 steel cable (1.344). I wasn't sure where to go with the information I have to calculate the sag. Thank you for your guidance and input! There doesn't seem to be a simple online calculator for this, I seem to be missing variables that I am unaware of.

 

[anorlunda]

OK, I used the online calculator for you using your numbers.

If you pre-tension the wire 1 pound, the sag is about 15.7 feet.
If you pre-tension the wire 10 pounds, the sag is about 1.3 feet.
If you pre-tension the wire 100 pounds, the sag is about 0.13 feet.

Safe working tension is about 300 pounds.

 

[Nidum]

If necessary there is a relatively easy calculation possible if we simplify the problem a little .

To some extent it is trial and error . Let's start with a safe tension for the wire and see where that gets us . 2000 lb breaking strength is quoted so let's say no more than 10% of that as first guess .

Will your calculator accept that as an input or do we start working this all out ourselves ?

 

[sophiecentaur]

To some extent it is trial and error .

Why is it not just a matter of some simultaneous equations?

 

[Cjbsurf]

Wow, thank you anorlunda, nidum and everyones input! I just got back home and I was pleasantly surprised to see your useful replies. I am extremely grateful for your willingness to help in an area that I have no skill in yet!

 

[CWatters]

In case it's not obvious, the key is not to try and tension the wire in an attempt to remove all of the sag. It will break or pull your pillars over.