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

In summary, the conversation is about suspending a 1/8 steel cable horizontally between two concrete pillars, with stationary objects weighing 3 pounds hanging from it. The cable has a breakstrength of 2,000lbs and the goal is to find out the force and sag in the cable. The solution suggested is to use a catenary calculator and start with a safe tension for the wire, as trying to remove all sag could result in the cable breaking.
  • #1
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!
 
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  • #3
Depends largely on how much you pre tension the wire . What do you intend to do about this ?
 
  • #4
Nidum said:
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.
 
  • #5
Doesn't matter that much when the wire is actually tensioned - what matters is that it is a user controlled input ?
 
  • #6
Nidum said:
a user controlled input
Meaning a design variable?
 
  • #7
Nidum said:
Doesn't matter that much when the wire is actually tensioned - what matters is that it is a user controlled input ?

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

You need a catenary calculator. There are
Nidum said:
Depends largely on how much you pre tension the wire . What do you intend to do about this ?
Nidum said:
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.
 
  • #8
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.
 
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  • #9
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 ?
 
  • #10
Nidum said:
To some extent it is trial and error .
Why is it not just a matter of some simultaneous equations?
 
  • #11
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!
 
  • #12
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.
 

1) What is the purpose of calculating sag and tension for 1/8 steel cable?

The purpose of calculating sag and tension for 1/8 steel cable is to determine the appropriate amount of tension to apply to the cable in order to ensure it can withstand the expected loads and maintain its shape and stability.

2) How is the amount of sag and tension for 1/8 steel cable calculated?

The amount of sag and tension for 1/8 steel cable can be calculated using a mathematical formula that takes into account the weight of the cable, the distance between supports, and the expected loads that the cable will need to withstand.

3) What factors can affect the amount of sag and tension for 1/8 steel cable?

The amount of sag and tension for 1/8 steel cable can be affected by various factors such as the weight of the cable, the distance between supports, the expected loads, temperature changes, and environmental conditions.

4) Why is it important to calculate the amount of sag and tension for 1/8 steel cable?

Calculating the amount of sag and tension for 1/8 steel cable is important because it ensures the cable will be able to withstand the expected loads without breaking or losing its shape. This helps to maintain the safety and stability of any structures or equipment that rely on the cable.

5) How can I ensure the accuracy of my calculations for sag and tension in 1/8 steel cable?

To ensure the accuracy of your calculations for sag and tension in 1/8 steel cable, it is important to use the correct formula and input accurate and precise measurements. It may also be helpful to double check your calculations and consult with other experts in the field.

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