Modulus of Elasticity for guy wire
Modulus of Elasticity for guy wire
(OP)
ASTM A475 lists the properties of several types of galvanized stranded cables used for guy wire. I was looking for a reference for the modulus of Elasticity (MOE) of these cables. It should be less than solid steel rod since as you load the cable it unwinds the individual strands a little and it probably depends on how much load is applied.
To further complicate matters the ASTM A475 lists the diameter of the strands with galvanizing and calculates the cable area including the galvanizing thickness (I think). Since zinc has a different modulus than steel, will the effective cable modulus be dependent on the steel area or the total stranded area?
To further complicate matters the ASTM A475 lists the diameter of the strands with galvanizing and calculates the cable area including the galvanizing thickness (I think). Since zinc has a different modulus than steel, will the effective cable modulus be dependent on the steel area or the total stranded area?
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RE: Modulus of Elasticity for guy wire
My edition is October 1968.
RE: Modulus of Elasticity for guy wire
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I have been called "A storehouse of worthless information" many times.
RE: Modulus of Elasticity for guy wire
http://www.slideruleera.net/
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I have been called "A storehouse of worthless information" many times.
RE: Modulus of Elasticity for guy wire
I glanced around their web site a little to see if you can order or download it but I didn't see it. I got this some time ago from them by snail mail. There web site is http://www.wrca.com.
You're asking the right question though. I suspect many people don't model the correct stiffness of cable in structural models.
RE: Modulus of Elasticity for guy wire
We are currently using 28,900,000 psi but I think that is too high. It might be correct if the cable was a solid steel rod. Someone said 23,500,000 psi was correct but they can't cite a source for the data and I wanted to have some verification before I switch to something else.
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I have been called "A storehouse of worthless information" many times.
RE: Modulus of Elasticity for guy wire
However for the purposes of preliminary design, or if manufacturer's data is truly impossible to obtain, you can use some rough rules to get an even rougher estimate:
(1) The effective cross sectional area of actual material in a twisted wire rope will usually be between 0.48 and 0.76 times the gross area, where the gross area is calculated on the basis of the nominal diameter. The lower values tend to apply to hollow-cored cables, while the upper values tend to apply to strand-cored cables.
(2) The effective Young's modulus will usually be between 0.41 and 0.72 times the material's actual value. This factor allows for the fact that the individual strands of material are twisted into a spiral pattern rather than running directly from end to end. The actual value depends upon the winding pattern that is used.
The product of these two "effective" values is an estimate of the axial stiffness, ie the "AE" value that you would use in the PL/(AE) formula.
RE: Modulus of Elasticity for guy wire
E = 18800/((.05)(0.1497))
so E is 2,511,690 psi which I think is about 10% of the value that it should be. Are my figures correct? Why is E so low.
TIA
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I have been called "A storehouse of worthless information" many times.
RE: Modulus of Elasticity for guy wire
RE: Modulus of Elasticity for guy wire
If I know that E=(P/A)/(dL/L) and for a elongation of .05 we get E = (P/A)/0.05 and if we say that E is reported as 25,000,000 psi, then the stress in the cable is (0.05)x(25,000 ksi) or 1250 ksi which is very strong cable.
So there must be some empirical formula to give the elongation for the cable unwinding in addition to PL/AE elongation.
As a side note, does anyone know how to type a capital Greek Delta in this forum? I used dL to represent delta L but was trying to put in a small triangle.
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I have been called "A storehouse of worthless information" many times.
RE: Modulus of Elasticity for guy wire
RE: Modulus of Elasticity for guy wire
RE: Modulus of Elasticity for guy wire
The 5% elongation is a maximum plastic strain for the material, so it's no wonder an elastic calculation is not giving you the right modulus.
Further, cable is a machine, not a material. Each time a cable is loaded in static tension to a new, higher value, the wires in the cable will stretch/slide/unwind and in general redistribute. This is called "taking a set" in the parlance. It looks like a plastic strain, but the material in the individual wire strands may not have actually reached its yield point. Once you've stretched a length of cable to some new maximum load, it will generally follow a linear load/displacement curve from there on, provided it never gets stressed beyond that original proof load, and unless the cable is also rolling over sheaves or pulleys, in which case further motion/redistribution of the wires will occur. Aircraft control cables have take-up mechanisms to account for the relief that occurs over time and use.
RE: Modulus of Elasticity for guy wire
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I have been called "A storehouse of worthless information" many times.