modulus of elasticity for guy wire
 

modulus of elasticity for guy wire
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?
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check page 30 of the uss tiger brand wire rope engineering handbook published by united states steel. this page provides approximate moduli of elasticity for a number of wire ropes. anywhere from 12e6 to 25e6.
my edition is october 1968.
i re
i found a pdf copy of in on slideruleera's web site.
i've got a manual called "technical data" from wireco. it list moduli from 8e6 to 15e6 psi. it also says you have to use something they call "metallic area" instead of the nominal area when computing rope stretch.
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
thanks for the link, i'll take a look there.
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.
a cable's axial stiffness should always be obtained from the manufacturer, or determined from tests on a sample of the particular cable.
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.
someone pointed out that the minimum elongation is specified as 5% in a475 for hs grade wire. if i re
my factor (2) above could explain things if you were calculating eeffective at 50% of eactual. the best i can suggest to expain the rest of the discrepancy is that the 5% elongation and the 18,000 pound rbs do not correspond directly.
the only thing i can think of is that the equation for young's modulus is stress/strain and it applies to a solid rod and is probably not applicable to a stranded cable. the cable will deform partially due to pl/ae and more to the twisting of the strands.
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.
in the aisc steel design guide,the e for cables is listed at 14000ksi