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Re: [theguy] An online impact force calculator:
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jt512
May 19, 2010, 12:01 AM
Views: 13625
Registered: Apr 12, 2001
Posts: 21904
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theguy wrote: jt512 wrote: JimTitt wrote: The UIAA decided way back in the 70´s that a 80kg solid weight represents the impact of a 100kg (in fact 101 and a little bit if I remember rightly) climber after tests by Troll who made some of the early harnesses. Jim, I'd have to see how that result was derived and convince myself of its validity before I'd incorporate it into a model. Jay While you are not explicitly stating that the weight in your calculator refers to the climber's weight rather than the test weight, many users may infer this; if they do, you are already (apparently unknowingly) incorporating the UIAA result in your calculator by basing your calculation in one scenario on impact force ratings provided by the UIAA. Your options would appear to be: a) Make it explicit that the weight refers to the drop test weight rather than the climber's weight when UIAA impact force ratings are used b) Make it explicit that the weight refers to the climber's weight and correct for the results used in the UIAA impact force ratings
The weight you enter in the calculator is the climber's weight, regardless of whether you check the "rope modulus" button or the "impact force rating" button. If that results in the impact force being too high because the model assumes a rigid mass, then so be it—it's a model. There are many factors in a real-world fall that the model does not take into consideration, such as the dynamic nature of the belay, friction between the rope and the rock, etc, etc, etc.
In reply to: jt512 wrote: the impact force on the belayer is assumed to be a percentage of the impact force on the climber. Therefore, the impact force on the belayer is higher under the friction-adjusted model than under the standard model. Jay, you're usually not a fan of assumptions, especially when they're demonstrably false; to maintain a consistent stance, you may wish to adjust this assumption.
First of all, there are lots of assumptions in a model that are "demonstrably false," in terms of how things behave in real life. For instance, as mentioned above, there is an assumption in these impact force models that the belay is perfectly static. But that said, what are you talking about when you say that it is demonstrably false that impact force on the belayer is proportional to the impact force on the climber? That assumption is made in every model of impact force I've ever seen. I think you've misunderstood something.
Jay
(This post was edited by jt512 on May 19, 2010, 3:45 AM)
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Edit Log:
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Post edited by jt512
() on May 19, 2010, 3:44 AM
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Post edited by jt512
() on May 19, 2010, 3:45 AM
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