Does Wire Rope Strength decrease as it gets longer? 1

[anchorengineer]

I have a 5/16" wire rope extending over 900ft and it will be in constant tension (hanging). The Minimum breaking strength is 8520 lbs and the safe working load is 1700 lbs. It will need to hold a maximum of 1000 lbs. I thought I read somewhere that strength decreases does for nylon rope but what about wire rope?

 

[dianium500]

Strength is based on force over a given area, so it doesn't get weaker. What you may find is that the longer the rope, the more it will elongate and you will need to determine if that elongation is acceptable. If not, you will need to reduce the load due to deflection. See Hooke's law.

 

[Compositepro]

The weight of the wire rope will be significant, and it adds to the load on the rope.

 

[CANPRO]

For a hanging load of that length you might get significant sway in the line as well (assuming this is exposed to wind). If both ends are restrained you might build up a bit of stress due to temperature changes over that length as well.

Great point by Compositepro, you're probably adding 300-400 lbs of cable to the equation.

 

[BridgeSmith]

I get an weight for 900' of 5/16" galvanized wire rope as about 155 lbs (17.3 lbs per 100ft from the one supplier I looked at).

 

[EngrPaper]

Depending on the elongation, you may need to take into account the reduced area of the rope. Engineering stress is acceptable in most cases, but you may want to double check the transverse strain using Poisson's ratio to see how much your cross sectional area has reduced.

 

[TLHS]

The strain is constant. The effects of reduced area aren't any different with a long wire rope than a short wire rope.

 

[miningman]

This subject is something that miners and mining engineers take rather seriously. With 50+ men in a cage hanging off the end of a wire rope, with perhaps a 2-3000 foot drop when something goes wrong, you better believe we know our factors of safety and practicalities quite well. In addition to all previous comments, my first questions would be how old is the rope, how many broken strands or degree of corrosion is evident, has the rope suffered physical damage in terms of kinking in its earlier life, what is the ratio of rope diameter to the diameter of the proposed winch or winches previously used. ????


Depending on the consequences of the rope breaking and the load dropping , perhaps this seems excessively anal , but with men at the end of the rope , these factors are critical.