GUY WIRE TESTS
Looking for equipment for the tower rigging, I found two types of wire rope hardware:
For both tests, I used 1/8" aircraft cable, (galvanized steel with 7/19 construction) which has a nominal breaking strength of 1800 to 2000 pounds. In the heavy lifting world, the working load should never be more than 1/4 of the breaking strength. A 1/8" cable should be used for loads that don't exceed 500 pounds.
Two U-clamps were secured to each end of each cable, with a 6" turn-back around a thimble. I attached a come-along and a load cell to each end of the ropes, and use some links and shackles to make connections. I placed a measuring tape on the floor beside the cable, but in the end it wasn't helpful because the photos aren't clear. I took pictures of each test to record the maximum load each cable would resist.
All strength figures are given in pounds. "SWL" means "Safe Working Load".
All cables have guaranteed minimum strength values from MIL-W-1511 Standard.
Cables that do not conform to this standard may not have equal strength.
Strength of 1/4" and 3/8" U-clamps extrapolated from 1/8" cable tests.
Segments of 1/8" aircraft cable (galvanized steel with 7/19 construction) were fabricated with two different types of wire-rope clips to demonstrate the cost-benefit of using cheaper clips.
Rated strength of cable = 2000 Lb.
Princess Auto (China) (80 cents per clip)
Load applied in steps.
Failure occurred at the first cable from the left, where the clamp could not maintain enough friction to stop the cable from sliding through.
Crosby Hardware (USA/Canada) (3 dollars per clip)
Load applied in steps. Length measured at 120 Lb = 25-7/16".
Failure occured at 2nd clamp from the right, where the cable broke due to stress concentration at the clamp.
Clip efficiency = 1640/2000 = 80%
Elongation = 3/16" per 1160 pounds = 0.00016"/Lb
Check with Loos & Co.
Stretch during test higher than theoretical due to thimbles deforming.