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## Re: [TowerTalk] PIPE ANCHORS

 To: Jim Lux Re: [TowerTalk] PIPE ANCHORS Grant Saviers Mon, 31 Oct 2011 13:44:32 -0700 mailto:towertalk@contesting.com>
 ```You are correct that a larger tube wins for same amount of steel. My comparison was same size/same moment and showed the extra steel needed for round in a 4" shape. The #/ft measure was a bad choice on my part. It should have included "for a given size" since otherwise a very large diameter thin tube has a higher moment but is useless structurally (unless it is pressurized as in liquid fuel rockets or Coors cans). Grant KZ1W On 10/31/2011 6:11 AM, Jim Lux wrote: > 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 > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] pipe anchors, (continued) 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 Re: [TowerTalk] PIPE ANCHORS, K8RI on TT