Wire Rope Ratings

[Josh2008]

Hello all,

I'm new to lifting and rigging, and I'm checking equipment spec'd out by a designer.

A wire rope sling with an end looped and crimped by a swaging sleeve that passes through a shackle creates a very tight bend radius. Bend radius' reduce the strength of the wire rope. I have found D/d ratios recommended for different constructions of ropes, but due to this type of connection and application, the calculated ratio is very small. How is this typically put in practice? Most commonly the wire ropes pass over large sheaves, therefore the ratios are high and meet literature recommendations (such as the Wire Rope User Manual), however this isn't my case.

Any suggestions on how to properly check this, or other literature to reference?

To be honest, I'm starting to think that swage fittings and shackles might not be the best duo. Maybe an open spelter socket is better, as there would be no induced rope bend.

Attached is a picture of the application I'm referring to.

J

 

[Josh2008]

Forgot the Pic

 

[dhengr]

Josh:
I’m old enough so I don’t buy every edition of every new code on every topic, I buy them if and when I need one. You might want to look for the ASME codes on Below the Hook Lifting Equip., OSHA, and various industry standards. Look for other threads here and on the Struct. forum for rigging, lifting, lifting lugs, spreader beams, and the like.

Your comments and D/d ratios kinda relate to two different things. On the one hand you are talking about wire rope which runs thousands of times per week over a sheave or on a winch drum, etc., your D/d, from the Wire Rope Handbook, a fatigue life problem on crane lifting (running) ropes, etc. An open spelter socket on some end fitting, a pin end socket or closed end socket, for example, is appropriate for pendants on crane booms, and the like. They are a fixed length and connected and disconnected many times and coiled up.

On the other hand, the slings you show in your picture are common lifting slings. Get a good handbook from someone who makes and sells these, there will be much design and rating info. in these handbooks and catalogs. The slings are basically rated as a single part wire rope, of the construction and grade of rope used, this controls the sling cap’y. Draw a free body diagram, P in the main part of the sling; and P/2 in each of the two halves of the loop, and the swagging is stronger. These slings are commonly looped over themselves (d/d) to form a choker hitch. Obviously, you can damage them by loading them over a knife edge, but they are commonly used with reasonable sized shackles and the like. And, a number of the different codes and industry stds. will talk about proof testing equip. like this when new, and cap’y. tagging and marking it. Then regular field inspection for damage or excessive wear and tear, and some limits on same.

Get some of these other handbooks, catalogs, textbooks, codes and standards, and give er hell. It ain’t brain surgery, but you are right to be concerned and conservative, which many riggers are not, they just want to get er done. Inspect equip. regularly and be safe out there.

 

[DAVIDSTECKER]

Probaly the first thing that would fail is the crimped connection.
A steel thimble adds support to the wire rope as it goes over the shackle.
All methods of making an eye or even a knot in a regular rope have a general de-rating factor. Your wire rope supplier should be able to provide them to you.
A good supplier made make up cables with specific load ratings and some even proof test them for you.
The angle between the wire ropes also de-rate lifting capacity, check out a manufactures web site like Crosby or C-M.

 

[boo1]

Sockets (poured or swaged), mechanical splice with thimble or loop, wedge socket, or clips with thimble are the most commonly used. You did not give the application, what country equipement is used, type/size/material of wire rope, D/d ratio or the shackle size. But I can provide general help or recommendations.

Running a choker over a shackle can give high bending and tensile stresses. Typically only used for temporary and low loaded applications. You must use a thimble to reduce the stress concentrations, tight radius and fiber crushing. The D/d wire rope ratios are for sheaves and running wire.

The efficiency varies with the type of termination:

Type of Termination Eff w/IWRC Eff/FC
Wire Rope Socket poured 100% 100%
Swaged 100% n/a
Mechanical splice
1" Dia and less 95% 92.5%
1" - 2" Dia 92.5% 90%
2"-3.5" Dia 90% not established
Thimble Splice-Hand tucked (carbon steel)
1/4" 90% 90%
3/8" 88% 88%
1/2" 86% 86%
3/4" 82% 82%
7/8"-2.5" 80% 80%
Wedge 75%-90% 75%-90%
Clips w thimble 80% 80%

Sounds like you are treating these assemblies as rigging. How are your assemblies being tested? What is your tagged rating? Are the assemblies retested periodically? Are they inspected periodically?