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## Re: [TowerTalk] Antenna loads for rohn 45

 To: K7LXC@aol.com Re: [TowerTalk] Antenna loads for rohn 45 jimlux Sun, 18 Jul 2010 12:12:02 -0700 mailto:towertalk@contesting.com>
 ```K7LXC@aol.com wrote: > > In a message dated 7/17/2010 7:47:04 P.M. Pacific Daylight Time, > towertalk-request@contesting.com writes: > >> I doubt solid legs would change the load rating much, but they would be > very nice for towers installed in corrosive locations. > > Umm, actually it would change the load rating significantly. Especially > since tower capacity is a direct function of leg strength. > I'm not so sure about that. Most towers are limited by the buckling load on the various short segments of tubing which are quite slender (that is, you consider it a slender column from one joint where the diagonal or horizontal brace attaches to to the next. The buckling load is proportional to the Young's modulus (stiffness of the materials, the radius to the 4th(!) power, and inversely proportional to the length squared. A tube and a solid bar don't have much difference here.. (that is, the term on top is Router^4-Rinner^4... going from a medium thickness wall to a solid doesn't change it a whole lot. Here's an example, giving relative strength compared to a solid rod Router Rinner Buckling 1 0 1 1 0.1 1.00 1 0.2 1.00 1 0.3 0.99 1 0.4 0.97 1 0.5 0.94 1 0.6 0.87 1 0.7 0.76 1 0.8 0.59 1 0.9 0.34 You can see that with a 0.2" wall on a 2" tube, you've got about 60% of the strength for less than 40% of the material. The amount of material (cost) for thin wall tubes goes roughly as a function of the diameter, while the buckling load goes as the fourth power. It's usually better to go to a larger diameter tube to get more strength, unless there's some constraint on tube size. here's a chart comparing buckling strength for constant wall thickness, and assuming cost is proportional to cross sectional area. Router Rinner Buckle Area strength/\$ 1 0.9 0.3439 0.19 1.81 1.1 1 0.46 0.21 2.21 1.2 1.1 0.61 0.23 2.65 1.3 1.2 0.78 0.25 3.13 1.4 1.3 0.99 0.27 3.65 1.5 1.4 1.22 0.29 4.21 1.6 1.5 1.49 0.31 4.81 1.7 1.6 1.80 0.33 5.45 1.8 1.7 2.15 0.35 6.13 1.9 1.8 2.53 0.37 6.85 Or here, where I held the cross sectional area constant Router Rinner Wall Buckle Area strength/\$ 1 0.81 0.19 0.5775 0.35 1.65 1.1 0.93 0.17 0.72 0.35 2.07 1.2 1.04 0.16 0.89 0.35 2.53 1.3 1.16 0.14 1.06 0.35 3.03 1.4 1.27 0.13 1.25 0.35 3.57 1.5 1.38 0.12 1.45 0.35 4.15 1.6 1.49 0.11 1.67 0.35 4.77 1.7 1.59 0.11 1.90 0.35 5.43 1.8 1.70 0.10 2.15 0.35 6.13 1.9 1.81 0.09 2.40 0.35 6.87 One can take this to an extreme: aluminum beverage cans have walls that are about 0.0005" thick (thinner than household aluminum foil), or actually thinner at the top and thicker at the bottom. But as anyone who has demonstrated column buckling by standing on a can can tell you, you get real subject to small imperfections.. If you make a solid bar, it weighs more, which increases the load on the bottom just from the tower weight, too. _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] Antenna loads for rohn 45, (continued) Re: [TowerTalk] Antenna loads for rohn 45, Dave Tipton, W5DMT Re: [TowerTalk] Antenna loads for rohn 45, Steve Gehring Re: [TowerTalk] Antenna loads for rohn 45, Roger (K8RI) Re: [TowerTalk] Antenna loads for rohn 45, Steve Gehring Re: [TowerTalk] Antenna loads for rohn 45, Roger (K8RI) Re: [TowerTalk] Antenna loads for rohn 45, john Re: [TowerTalk] Antenna loads for rohn 45, Roger (K8RI) Re: [TowerTalk] Antenna loads for rohn 45, K7LXC [TowerTalk] Antenna loads for rohn 45, Jim Thomson Re: [TowerTalk] Antenna loads for rohn 45, K7LXC Re: [TowerTalk] Antenna loads for rohn 45, jimlux <= Re: [TowerTalk] Antenna loads for rohn 45, Roger (K8RI) Re: [TowerTalk] Antenna loads for rohn 45, john [TowerTalk] Antenna loads for rohn 45, Jim Thomson