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## [TowerTalk] earth anchors & screw-in anchors

 To: [TowerTalk] earth anchors & screw-in anchors shr@medinaec.com (W0UN--John Brosnahan) Wed Feb 26 15:24:55 2003
 ```> >There's an old engineering exercise where you have a steel piano wire and >a big rope in parallel supporting a weight. The piano wire is very stiff, >so takes all the load, and fails. Another exercise is the "welded gusset >on the bracket" that makes it weaker, because it stiffens it, and actually >increases the stress. Jim-- You raise some interesting points, but the analogy above does not apply because the guys are not in parallel. They are separated by a long section for relatively flexible tower. So the tower does the equalizing. Same with the three guys at any given level. The tower moves around enough to equalize the tension in the three guys (under static load--winds are different of course). >The Rohn approach is a good one, sort of following the "put all your eggs >in one basket, and then watch that basket very carefully" >philosophy. Design the one anchor with a huge margin and then hang >everything off of it. Of course, if you "cheat" and put an unreliable or >underspecified anchor in, then you've defeated the purpose. Actually Rohn does not put all of their eggs in one basket for many of their larger towers and uses separate guy anchor points. Rohn certainly has an "equalizer plate" that must serve some purpose but I have never been totally convinced that it is necessary. One example--if you have an odd number of guy levels then the middle guy is always in the middle of the equalizer plate and receives no benefit from the equalizing. I really don't think it is all that complicated (but then I am not a PE but rather a physicist with a lot of tower experience). I think the flexibility of the tower itself is greater than any equalizing that might be done in (at least) the smaller Rohn towers (25/45/55). I have done a lot of towers up to the 200 ft level from the tropics to the arctic region and have seen no functional difference whether I use one guy point or multiple guy points in each direction. The multiple guy points do have the advantage of no single-point-of- failure. The only weak link I have seen is the corrosion of the guy rod in the soil over long periods of time. I strongly suggest following Rohn's suggestion about covering the guy anchor that is not in the concrete but still under the earth is a tar/paper wrap. Other than these thoughts I don't have anything much more to add and I am always open to better ideas as long as there is some scientific justification. Just hate to see things made more complex than they really are. I guess Occam's Razor is my guiding philosophy. 73--John W0UN ```
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