Calculating Young's Modulus of Tight Rope 7

[Mandrill22]

Does anyone have experience calculating stress/strain of a steel rope? A tightrope someone would be walking on is, from what I can tell on the web, 5/8" OD, with a 7x19 configuration, meaning 7 smaller braids of 19 strands each. The material is galvanized steel, details below:
Construction: 7x19 (12+6+1) WSC
Finish: Hot Dipped Galvanized
Lay: Right Hand Regular Lay
Load Bearing Outer Wires: 114
Fill Factor: 0.57
Tensile Grade: Improved Plow Steel (IPS)
Minimum Breaking Strength: 37,000 lbs.

All of the information I've been able to find has only considered axial loading. Since the it's like a point load on a beam, it makes the calc more complicated.

 

[3DDave]

Because of the twists the intentional result is that wire rope doesn't have much resistance to bending in comparison to similar section areas of solid members. Essentially each fiber/wire is on both sides of the neutral axis and that cancels bending stresses out.

If there's something more required, you'll likely need to perform testing with the exact item interface to explore the reaction/result.

 

[rb1957]

a tight rope is not a beam. The rope deflects and the vertical load is reacted as a component of axial loading of the rope. Properties of wire rope are well known, talk to a supplier.

The weight of this steel rope would be significantly more than the weight of the walker.

another day in paradise, or is paradise one day closer ?

 

[Mandrill22]

I understand that it isn't a beam, and I agree in terms of the strands, but the rope as a whole sags due to the walker. It's taught and straight before the point load is applied.

 

[desertfox]

Hi Mandrill22

Do you know what the initial tension is in the rope prior to the walker stepping on it?
Like rb1957 states the wire will resist the weight of the walker by tension similar to pulling a wire rope over sheaves.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[rb1957]

that may be catenary action. The rope is axially loaded.

"All of the information I've been able to find has only considered axial loading. ..." ... that's what you need.
"... Since the it's like a point load on a beam, ..." ... no it isn't
"... it makes the calc more complicated." ... yes, but the complication is to determine the axial load in the rope.

another day in paradise, or is paradise one day closer ?

 

[desertfox]

I might be over simplifying this but if you know the force generated by the walker ie mass x gravity and the initial tension in the rope then you could estimate the resultant tension in the cable by triangle of forces possibly. With the stretch in the cable due to walkers force you could then workout the cable sag in the centre of the cable which I guess is the important point.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[dvd]

Page 3-9 gives a formula that can be rearranged for E -

 

[TheTick]

There may be some relevant info available on sites dedicated to rigging.

 

[Denial]

On my web site (

http://rmniall.com)

you will find a free downloadable spreadsheet that rigorously solves the problem of an axially stretchable cable carrying a point load in addition to its self weight.[ ] By "rigorous", I mean the cable has zero bending stiffness, finite self-weight, and a constant stretchability. [ ] Its deflected shape is one catenary curve one side of the point load, and a different catenary curve the other side.

 

[geesaman.d]

The detailed behavior that would lead to an accurate estimate of lateral deflection strikes me as wildly nonlinear in nature.

Also, is this pre-stretched? I know bicycle brake and shifter cables have a 'set' induced in production because raw wire rope does set under load.

I'd start with some testing at smaller scales using the actual wire rope and walker's weight. From there the system should behave similarly, just at a smaller magnitude.