Bad Anchor Hardware

[Peter_Puget]

So if the one from my hardware store says working load 500# thats rated?

[jkrueger]

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i was re-reading your questions and i think if you put out exaclty what you are asking then a better answer could come about...

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In this case, answers have led to more questions... but I think it's been pretty well covered from many angles. Just trying to make the crags out there a bit safer and more unjoyable.

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are you setting up a new anchor drilling holes and placing bolts and hangers??

are you replacing crappy webbing and rings??

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Both - you have to deal with what you're given, which varies from situation to situation. I am of the opinion that I had better be prepared for the worst case scenario... Though it's not likely, what starts out as replacing crappy webbing can turn into drilling holes and placing bolts and anchors, so it's all relevant.

[jkrueger]

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Originally posted by Peter Puget:

So if the one from my hardware store says working load 500# thats rated?

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Who are you, the Devil's Advocate?

[willstrickland]

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Originally posted by Peter Puget:

So if the one from my hardware store says working load 500# thats rated?

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This was precisely my point PP (ahh ha, whazup peepee?). Anyway, the testing methods employed can produce very drastically differing results. One must wonder what exactly the "Rated" chain number comes from. In civil engineering work, materials typically have a small FS built into the ratings 1.2-1.4 in my work, and the designers further incorporate additional FS into the design based on use, loading, lifespan, etc. FS tends to come from either the mean where the FS places the rating well out of the std deviation, or from the weak end of the std dev where you gain additional FS.

I wouldn't be suprised if the chain is simply rated at the mean tensile failure point, given a 1.2 FS and called good. Personally, I have no hesitation about using stainless chain (not for hangers, which is kinda stupid) rated around the same as the biners...roughly 20kn or 4500lb. You have redundancy in the system with two anchor points, just be wary of rapping off the links as some people may use the bottom links to TR or lower through, steadily wearing through the link.

[allison]

What is mean tensile failure point? Is that the amount of stretching the chain will take before failure? Could chain be only tested that way? Chain hoists take dynamic load all of the time, though the rating of the motor is way lower than the rating of the chain.

Here I was worried about getting too technical and a civ engr comes along! Touche!!

[willstrickland]

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Originally posted by allison:

What is mean tensile failure point? Is that the amount of stretching the chain will take before failure? Could chain be only tested that way?

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It's essentially the force loading along the linear axis (imagine pulling a section of round bar stock from both ends) at which failure occurs. While watching these tests what happens is that the material reaches a "yield" point where it begins to elongate. This yield point is actually higher than the load required to continue elongation and hence is usually the failure loading.

Since failure would rarely come from an extremely high static load, this is only useful data to an extent. Most failures that occur in my field are due to fatigue, or repeated stress loadings, which eventually cause a lateral shearing when a load is placed along a non-ideal loading plane. Dynamic loading gets extremely complicated, and the failure mechanism is likely to be a comination of tensile and sheer stresses.

This is not the only way to test. There are testing machines designed specifically to cyclically load a material to simulate fatigue. The testing typically works two ways: 1. Apply a certain number of cycles at a pre-determined load to a material and then peform other tests,such as tensile testing or 2. Apply a pre-determined load in cycles until material failure.

Whew, it's been a long time since materials class, the only testing data I see much anymore is asphalt/subgrade sections and fasteners (bolts etc for signal poles, signs, lightpoles). Soon no more numbers! No more engineering! There's gotta be a sweet niche position out there for a guy with a BCE and a MS in Rec and Park Admin.

[Peter_Puget]

Wazzup WS? Your analytic powers never cease amaze me. Look at the times of our posts. Jeez, you be a goof ball.

When we talk about ratings we need to know what we mean. As has been mentioned working load ratings are/can be very different than failure point. Second “ratings” are always very specific and can be misleading if used as the sole criteria for selecting or determining which product to use. This is true of a wide variety of things. For example the so called “expectations gap” between the function of a audit of finacial statements and the public’s perceived understanding. Think of UL labels or the electric code. Also a rating doesn’t necessarily say anything about how the equipment will weather/age. Its ability to withstand abuse. For example, I think I’d prefer a non-SS bolt over a SS bolt when it’s only a day old but after a few years give me the SS., Add to this the fact that in the field an object’s “rate status” often cannot be determined. (Sidebar: if you checked out the Nate Beckworth link W posted and read any of his TRs you’d see that he bought the wrong bolts for rivets. Not slamming him by any means but showing that even very experienced climbers can make errors) A good anchor design takes all of these factors into account.

[willstrickland]

Ah ha! You got me there Puget, didn't even look at the times. Touche' mate.

[allison]

Thanks Will, that's sort of what I thought....and I haven't had the materials claases. Just a ton of field experience.

The fact that dynamic loading and stresses gets so complicated, well that's what I said in answer to the original question. Dynamic loads are really the part of rigging that is impossible to explain. As far as the wear issue, in my work everything is steel and our best method is visual inspection. Thank god we don't use aluminium!

[allison]

Erik, where are these construction workers you are talking about? Rigging is typically done with steel cable with swaged and thimbled eyes (rated), shackles (rated), steel biners (rated) chain hoists (rated), and not with unrated materials. Very similar to what we use in my work. We never fake it because we don't have the right stuff. There's too much danger and liability. Same with construction work.

Of course there is rated chain....haven't you ever seen a chain hoist?

As far as the 'what is rated' question...it's too complicated to discuss here, especially when you get into dynamic loads. There might be some stuff on the Petzl website on this, they talk about this sometimes.

Typically in my work we look at the load capacity of whatever we are using, and then incorporate a safety factor of 5 to 8 times that rating, but there are so many variables to that formula in doing safe overhead rigging....well it's just not worth getting in to.