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## [TowerTalk] Tower Bases

 To: [TowerTalk] Tower Bases spelunk.sueno@prodigy.net (EUGENE SMAR) Thu Feb 27 12:17:56 2003
 ```Tim: It seems to me (I haven't done the math) that you'd be better off taking the time and trouble to dig the deeper hole and pour concrete in a cubish form, rather than use long, cross-type footers to support a tower. Here's why. If you constructed the cross and fixed the tower to its center, any upturning moment (the wind trying to push the tower over) would exert a significant force at ground level. This in turn would be absorbed by the cross-concrete almost exclusively. There is, in your proposed design, insufficient earth (dirt) surrounding the concrete to aid this resisting force. This is the main reason that SS towers with appropriately designed foundations don't fall over - the dirt helps keep it upright. So the forces that are trying to turn the tower over are taken up by the concrete. However, the effect applies also to the concrete that form the cross. The wind force will essentially break the concrete cross(es) at the point they attach to the center. And the longer you make these cross arms, the more the lever effect will concentrate the force on the center attachment point of the downwind cross arm. I've recounted on this forum previously about my experiences with constructing towers in Haiti. These folks are resourceful enough to dig the SS towers' foundation holes (four per tower, one per leg!), and not have problems with cave-ins. (Although I believe they used machinery to dig the holes.) To get your proposed solution to work, one would have to provide considerable reinforcing bar and increased concrete tensile strength (I haven't done the math, as I said). The extra co\$t of this approach seems not worth the trouble. If absolutely necessary not to dig, one might be able to design a concrete cube, as others here have suggested, to sit on the top of the dirt. But this concrete structure would indeed have to be massive. (At some point the laws of economics supercede the laws of physics.) 73 de Gene Smar AD3F -----Original Message----- From: Tim Makins, EI8IC To: TowerTalk To: Date: Thursday, February 27, 2003 3:02 AM Subject: [TowerTalk] Tower Bases >Many years ago, at school, I remember seeing the illustration of how you >could move the world if you had a long enough lever. It occured to me >recently that the same idea could be used to construct self-supporting tower >bases, but, as I'm not an engineer, I thought I'd come to Towertalk to be >proved wrong. > >The idea is: Instead of the usual cube of concrete, how about using a >horizontal cross. Maybe 2 feet deep, and 2-3 feet wide, with an internal >rebar cage to prevent snapping. The length of each arm of the cross to be >determined by whatever formulas you guys use - I was thinking along the 12 >foot mark, as a discussion-opener. > >You will note that I haven't mentioned tower height, as obviously all the >parameters inter-relate. If you must have a figure, lets say 40-60 feet. > >The reason for this ? Well, I was thinking 'outback', and 'developing world' >here, where a mechanical digger isn't always available. Easier to dig slit >trenches than a big pit. Less problems from cave-in too. > >Sit down, take one of these beers, and discuss. > >73s, Tim EI8IC >www.qsl.net/ei8ic > >_______________________________________________ > >See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. > >_______________________________________________ >TowerTalk mailing list >TowerTalk@contesting.com >http://lists.contesting.com/mailman/listinfo/towertalk ```
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