tennsil strength vs working load limit

[heescha]

so when a tennsil strength is 1250lbs what is the working load limit

[headchange4u]

seuss posted a good explanation in this thread.

According to the Cordage Institute's Fiber Robe Technical Information and Application Manual Working Load is between 1/5 and 1/12 of a line's minimum breaking strength, depending on safety factors. In practice, I've rarely seen a working load that was less than 1/5. "Minimum Breaking Strength" is itself defined as being 2 standard deviations below the average tested breaking strength. I leave it to the engineers here to do whatever engineers do with this kind of information.

NOTE: Webbing is obviously different from "Fiber Rope" and the Cordage Institute is not a trade association for webbing manufacturers. Standards for webbing are set by the Web Sling and Tie Down Association. The standards for webbing (WSTDA-T-4) were revised last year. I haven't actually seen the new standards.

[heescha]

somewhat confused on what taht means!

[GrizzlyAdams]

somewhat confused on what taht means!

Attention class. Class! You in the back, with the cap on backwards, SHUT-UP!

Thank you.

Today's lesson is on breaking strength of rope. A rope maker tests a given kind of rope on a machine designed for this purpose. A piece of rope of a given length is attached to the machine, which pulls (and measures the pulling force) until the rope snaps. The pulling force for that particular experiment is measured, and the experiment is repeated several times on different pieces of otherwise identical rope. The breaking force on each experiment (also known as the tensile strength) may vary.

A statistical analysis of all the measured breaking strengths is done by computing the average breaking strength, and also the "standard deviation". This is a measure of how spread apart the different measurements are. You lot are too

HEY CAPMAN, SIT-DOWN ALREADY!

thick to grasp the subleties of standard deviation, but remember this : the number equal to the average breaking strength minus two times the standard deviation is so small that 97.5% of the experiments have breaking strengths larger than it. The rope maker reports this number as a "minimum breaking strength" with the confidence that in almost all repetitions of the breaking rope experiment, the breaking strength is higher than this number.

The "working load limit" is a small fraction of minimum breaking strength, chosen for engineering caution and also to account for less-than-controlled conditions you find in the field.

HEY CAPMAN. GET YOUR FEET OFF OF THAT GIRLS HEAD!
Capman, you annoy me. I'm tempted to test whether the tensil strength of this Spyderline I'm carrying in my pocket is greater than your body weight.

Class, in our next lesson we will review the spelling of common four letter words.

YES CAPMAN, I KNOW YOU KNOW HOW TO SPELL _THOSE_ WORDS.


Sheez, high school. Nothing but discipline problems.

Teacher Grizz

[Tobit]

CAPMAN must be neo.

[Ramblinrev]

"Standard Deviation ... aka "Universal Fudge Factor"

[CajunHiker]

I love it when Grizz gets all "mathy" on us.

[6 feet over]

Attention class. Class! You in the back, with the cap on backwards, SHUT-UP!

Thank you.

Today's lesson is on breaking strength of rope. A rope maker tests a given kind of rope on a machine designed for this purpose. A piece of rope of a given length is attached to the machine, which pulls (and measures the pulling force) until the rope snaps. The pulling force for that particular experiment is measured, and the experiment is repeated several times on different pieces of otherwise identical rope. The breaking force on each experiment (also known as the tensile strength) may vary.

A statistical analysis of all the measured breaking strengths is done by computing the average breaking strength, and also the "standard deviation". This is a measure of how spread apart the different measurements are. You lot are too

HEY CAPMAN, SIT-DOWN ALREADY!

thick to grasp the subleties of standard deviation, but remember this : the number equal to the average breaking strength minus two times the standard deviation is so small that 97.5% of the experiments have breaking strengths larger than it. The rope maker reports this number as a "minimum breaking strength" with the confidence that in almost all repetitions of the breaking rope experiment, the breaking strength is higher than this number.

The "working load limit" is a small fraction of minimum breaking strength, chosen for engineering caution and also to account for less-than-controlled conditions you find in the field.

HEY CAPMAN. GET YOUR FEET OFF OF THAT GIRLS HEAD!
Capman, you annoy me. I'm tempted to test whether the tensil strength of this Spyderline I'm carrying in my pocket is greater than your body weight.

Class, in our next lesson we will review the spelling of common four letter words.

YES CAPMAN, I KNOW YOU KNOW HOW TO SPELL _THOSE_ WORDS.


Sheez, high school. Nothing but discipline problems.

Teacher Grizz

For those of us with too much in common with ‘Capman’ & heescha, what would you recommend as the “small fraction” we can safely go by.

Per seuss, it’s “…Working Load is between 1/5 and 1/12 of a line's minimum breaking strength, depending on safety factors. In practice, I've rarely seen a working load that was less than 1/5…"

Does this mean that heescha’s 1250lbs tensile strength rope’s working load limit is 250? (1/5th of 1250) While we’re at it, does this mean a hammock supported by this rope can only hold 250 lbs. Or is it 500 lbs due to two support ropes ‘sharing’ the load. (Of course the hammock body would also need to be able to support the load, but lets not go there right now!)

No disrespect Teacher Grizz. Don’t you go by the “There are no stupid questions” philosophy in your class?

6

[GrizzlyAdams]

For those of us with too much in common with ‘Capman’ & heescha, what would you recommend as the “small fraction” we can safely go by.

Per seuss, it’s “…Working Load is between 1/5 and 1/12 of a line's minimum breaking strength, depending on safety factors. In practice, I've rarely seen a working load that was less than 1/5…"

Does this mean that heescha’s 1250lbs tensile strength rope’s working load limit is 250? (1/5th of 1250) While we’re at it, does this mean a hammock supported by this rope can only hold 250 lbs. Or is it 500 lbs due to two support ropes ‘sharing’ the load. (Of course the hammock body would also need to be able to support the load, but lets not go there right now!)
6

according to seuss then yes, heescha's working load limit is 250.

You need also to bear in mind that adding knots to a rope reduces the
working load limit significantly, by half is pretty common, depending on the knot.

You need also to bear in mind that the load placed on a rope is more than just the body weight. The angle of the rope with respect to the tree or support (under load) affects the force. The flatter the rope, the higher the tension and the closer to the rope's limit you are.

What fraction of minimum breaking strength is "working load limit"??? Different people use different fractions. 1/4 or 1/5 seems pretty common.

And yes, you can divide the "offered load" on the ropes by 2 because there are two of them.

FWIW, I use suspension rope that has a 2000 tensile strength. I know others that feel comfortable with rope that is close to heescha's 1250 tensile strength. I snapped mine though, and so moved up a notch in rope strength.

Grizz

[heescha]

wow, thank you Mr. Grizz. I appologize for not paying closer attention in class. I promise to do better in college!