On Jun 5, 2007, at 8:51 PM, Fred Sturm wrote: > Hi Ron, > I dunno. Those phrases "appreciable change in dimensions" and "no > practical significance" might be loaded (along with "measurable > proportions": who's measuring, and to what accuracy?). snip > Just the skeptic in me, and, possibly, > years of experience. Of course, I could be wrong, and I could be > misinterpreting my "years of experience." On Jun 6, 2007, at 7:38 AM, Ron Nossaman wrote: > I think you are, along with most everyone else. Most people seem to > think that music wire keeps stretching forever, but I don't think > that's the case. Do they go out every year and tighten the cables > of suspension bridges every year to pull the roadway back up level? > Anyone know? According to my dad, who, like me, is a junkie of trivia like this, much of which he gets from watching Discovery and History Channel Documentaries while we are all sleeping, the cables of suspension bridges are constantly being replaced. (Yes, I'd like to know how, too.) But he happened to have that much to add to what I actually called him about... He is a veteran utilities lineman of 38 years and explained the process with electricity transmission high lines, something not unlike the concept of suspension bridges. Here's my paraphrased edition: They call it "sagging" the line. An engineer calculates the amount of overpull, incorporating temperature, other load that will be added and the amount of projected sag, and it is pulled or "sagged" once. There is actually a device for measuring the load torque for electrical transmission wire. If it is done properly, it will likely never be resagged until it is replaced, unless changes in the infrastructure are being made. But, as he said, that wire doesn't have to be kept at a certain pitch. Just a certain height above the ground. So, "no practical significance" certainly is relevant here. That wire may indeed continue sagging over time, but not by an amount worth fussing over. I also remember "resagging" barbed wire fences on our farm, many, many, etc., times. We were often pulling and moving barbed wire fences for our cattle. You could pull barbed wire so tight it was near the breaking point (and would occasionally break), but still have to go back and repull the wire later. We often made the first pull with a truck or tractor before tying the wire off. It would usually get to a point after the second pull where it would work for our purposes (as in, not sag to the ground), and so unless the wire broke, we wouldn't have to pull it again. But we didn't have an engineer calculating our overpull either, and again, we weren't measuring pitch. Here again, "no practical significance" is relevant. Given my limited level of enlightenment, me thinks one could easily come to the conclusion that "no practical significance" would certainly be relative to application, and time elapsed. The amount of stretch which would enable pitch drop in a single piano wire pulled to 180 lbs, might very well be of "no practical significance" in most every other reason to measure elongation of steel wire. Jeff Jeff Tanner, RPT University of South Carolina -------------- next part -------------- An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/caut.php/attachments/20070606/00a90241/attachment.html
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