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RE: More RCSC questions

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Title: RE: More RCSC questions

>I don't really understand the
>differences between design for slip resistance at the factored-load level vs
>at the service load level, other than the obvious difference of whether one
>includes load factors or not. (Reference RCSC specification Section 5.4.)

Other  than the load level at which the check is performed, I do not see any difference either. As they are now, both checks are set up to prevent slip in the service-load range, regardless of the load level at which the check is made. I personally think the distinction is one that either needs to be made real or eliminated. Let me explain.

Within the Bolt Council (RCSC), there are those that advocate that the factored-load check is intended to prevent slip up to the factored load and that the service-load check is intended to prevent slip in the service range only. This segment says that the engineer must then decide whether slip resistance is required in the service range as a service consideration or in the factored range as a strength criterion. In theory, that's what all that stuff about the differing origins of the two checks in the Commentary means.

There are also those that think (me being one of them) that, whatever was the philosophical origin of the two checks, the checks as they are written are calibrated to result in the same basic connection. the Commentary actually says this. To me that means that they both check slip in the service-load range -- one just happens to do it at the factored-load level. If this camp is correct, it means that the decision can be based in most cases upon whether it is easier to use the factored or service calculation.

I tried, but was unsuccessful in getting all that differentiation about probability of slip out of the RCSC Commentary. I'm going to try it again for the next version, because more and more of my colleagues on the Bolt Council are agreeing that the two checks have in the end the same goal -- prevention of slip in the service-load range. Too bad I couldn't have been more persuasive sooner.

As I see it, RCSC has two choices: (1) keep what we have and eliminate the discussions about how the methods "differ"; and, (2) change what we have to one check on slip resistance up to the factored-load level and the other on slip resistance in the service-load range. If the latter path were chosen, then there would actually be a decision for the engineer to make.

There may be a need for the latter path. When slip is critical at the factored load level, such as in a bolted structure for a large dish-shaped microwave antenna (can't wait to bid on that project, can you?), even a tiny slip might change the surface curvature and make the dish somewhat useless. In this case, it is probably the factored-load level at which slip prevention is needed. For usual cases of slip resistance requirements, however, the service-load range criteria are sufficient.

I've babbled on way to much here. Sorry.

Charlie