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## Re: [TowerTalk] PIPE ANCHORS

 To: towertalk@contesting.com Re: [TowerTalk] PIPE ANCHORS Jim Lux Mon, 31 Oct 2011 06:11:31 -0700 mailto:towertalk@contesting.com>
 ```On 10/30/11 7:59 PM, Grant Saviers wrote: > Like your logic, but squares have more steel "further out" from the > neutral axis so they win (or at least moment calculators say so) > > see http://www.engineersedge.com/section_properties_menu.shtml > > Compare a 4" od x 3" id pipe with a 4" sq od x 3.5" id sq tube. Many > shapes are there to play with. > > About the same moments and the pipe is much heavier. 5.5 sq in cross > section of steel for the pipe and 3.75 sq in for sq tube, a 50% increase > in weight per foot for tube. > > And there is a diagonal moment calculator for squares (squares win in > all cases). > > What am I missing? (of course there is a lot more to structures than > this one number) > You're comparing a 1/2" wall round tube with a 1/4" wall square tube. Since the moment is Router^4-Rinner^4 the added wall thickness adds weight without much strength (tube is better than rod, as it were). If you make the weight/ft (cross sectional area) the same (I did it by making the tube bigger), you see the expected advantage for round. Try 4" square tube, 3" inside (1/2" walls) area (weight per length) = 7 moment = 14.6 Compare to 5" ID round tube, 4.01" id (1/2" walls) area = 7.01 moment = 18.0 If your constraint were "what's the strongest that will fit in a 4x4" square, then square tube will win, since even a solid 4" diameter round bar won't be as strong in bending: that r^4 term out to the corners. Large diameter thin walls is the strongest in bending and torsion, etc. BUT the practical problem is that as it gets thinner, small defects become a bigger problem. If you column load it, it's even worse (the standing on an empty aluminum can thing).. a tiny asymmetry in loading or the metal will lead to buckling. Yes, if you know the direction of the load, and it's always the same, then some other shape will be better (a long thin sheet, for instance) _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] pipe anchors, (continued) Re: [TowerTalk] pipe anchors, Chuck Sudds Re: [TowerTalk] pipe anchors, Jim Lux [TowerTalk] PIPE ANCHORS, sgtokie Re: [TowerTalk] PIPE ANCHORS, Grant Saviers Re: [TowerTalk] PIPE ANCHORS, R. Morris Re: [TowerTalk] PIPE ANCHORS, Jon Pearl - W4ABC Re: [TowerTalk] PIPE ANCHORS, Jim Lux Re: [TowerTalk] PIPE ANCHORS, Jim Lux Re: [TowerTalk] PIPE ANCHORS, K8RI on TT Re: [TowerTalk] PIPE ANCHORS, Grant Saviers Re: [TowerTalk] PIPE ANCHORS, Jim Lux <= Re: [TowerTalk] PIPE ANCHORS, Grant Saviers Re: [TowerTalk] PIPE ANCHORS, Dorn Hetzel Re: [TowerTalk] PIPE ANCHORS, Dorn Hetzel Re: [TowerTalk] PIPE ANCHORS, Jim Lux Re: [TowerTalk] PIPE ANCHORS, Kipton Moravec [TowerTalk] (Concrete filled anchors) was Re: PIPE ANCHORS, K8RI on TT Re: [TowerTalk] PIPE ANCHORS, Bill Gillenwater Re: [TowerTalk] PIPE ANCHORS, Jim Lux Re: [TowerTalk] PIPE ANCHORS, Dorn Hetzel Re: [TowerTalk] PIPE ANCHORS, K8RI on TT