Cable axial stiffness

[JT-1995]

Good morning! I am designing a horizontal lifeline and I have been researching for a couple days what material I want to specify. I believe I have a good understanding of the behavior of the lifeline and my calculations are going to hinge on the AE of the cable. I have a lot of great discussion on Eng-tips that the AE is manufacture specific and I believe I agree with that. I have failed at many attempts to find any manufacture information online willing to state AE for their product.

My thought is to spec a SALA NANO SRL with snap hooks to a horizontal 3/4" cable that will be installed through intermediate supports (properly designed plates with holes) and all suspended from a self supporting structural frame. I am searching for first the cable identification, I am thinking 7x19 wire rope, and I prefer stainless just because of the sliding snap hook will deteriorate the galvanizing over time. So searches for this product hopefully to find a manufacture and their stated AE have failed.

Any thoughts or redirection is greatly appreciated.

 

[phamENG]

Do you have a copy of ASCE 19? If not, you should get one if you're specifying structural wire rope or strand. Also, google "Wire Rope Handbook" - there's a pdf that comes up that's quite useful.

Yes, it will ultimately depend on the manufacturer. BUT, you can get in the ball park of what's reasonable and then specify your requirements. The contractor will then need to go to the manufacturer to get the information to prove conformance. If this is design build, find out the supplier they use and make some phone calls. If it's a reputable supplier/manufacturer, they'll have the requisite test data/certs.

You have two types of stretch - 'constructional' stretch which occurs as a result of the individual strands in the rope pulling together and the rope getting longer. This is generally inelastic and won't be recovered. The rest is pretty standard E for the base material. So if you specify pre-stretched wire rope, you can calculate your AE based on the actual A (sum of the area of each strand) and the E of the material.

That initial stretch is typically in the range of .0025L to .01L.

You may also want to look at ASTM A492 "Standard Specification for Stainless Steel Wire Rope."

 

[Compositepro]

Constructional stretch is a significant factor at lower tension range of a rope. If you can pretension the rope, it is not important anymore. If the rope must operate at high and low tension, you can use compacted wire rope, where the rope has been drawn through a die and the wire strands are deformed into wedges. This type of wire rope is much less flexible.

 

[JT-1995]

Thanks for the input.

My thoughts are to minimize the in field tensioning for the lifeline (what wire rope is specified not withstanding) and set the lifeline with human pulls and wraps at the connecting eyes. Using this small pretension (the final length of the rope is almost (is) the same as the original length) and assuming for a start that the E=14e6 and the actual diameter is .75 and effective diameter is .48
I calculate AE=4.02e6lbf. Continuing the calculation I find after the fall in my 12ft unsupported rope span the T is 14.6K and the rope deflects about 9in. But I need to make sure I am using viable AE's. I am going to specify pre stretched wire rope.

Thank you very much.

 

[azcats]

I came across this chart that included EA values years ago when performing similar calculations.

That company doesn't appear to be around anymore.

This was also in my archive.

Wire Rope Stretch

I cannot attest to the accuracy of either of these documents - provided for information only.

I don't know how much pretension or droop you're providing, but a tad of stretch can significantly increase the angle and reduce the tension. I know on my situation the cable tension went from an initial tension of something around 9 kips to down around 5 kips when stretched by about an inch. (this was an iterative calc)

 

[Denial]

JT-1995.[ ] It sounds as if you believe the cable stretchibility to be quite critical in your exercise.[ ] If so, you should consider investigating a range of possible values.

This can be a tedious iterative process (as Azcats has hinted and as you have probably already discovered).[ ] On my website (

https://rmniall.com)

you will find a spreadsheet that will do the arithmetic for you.

 

[JT-1995]

THANK YOU ALL FOR YOUR TIME!