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On Sun, 25 Jan 2004 11:33:38 -0500, "Ralph Mowery"
wrote: Yea, allow about 6 to 10 yards of concrete for starters. Not sure how big of a hole that would take right off in dimensions. That's in the ballpark of a small concrete house foundation, isn't it? That would be 162 cu ft (for 6 yards of concrete) or 10 x 10 x 1.6 ft, or 6 x 6 x 4.5 ft. For reference, 10 yards is the typical capacity of a cement mixer truck. For any project, you need to look at the total cost of installation and all components, not just the primary component. I figure I have as much invested in concrete as I do in the tower and mine is guyed. http://www.rogerhalstead.com/ham_files/tower.htm As you have shown there are many ways to pour the material . I am sure the tower maker has their recommendations. I doubt it would do much good to have it only 1.5 feet deep and 10 feet wide. I would think it would be Although it's not normally recommended to go that way, the weight is the stabilizing factor to be considered. poured in more of a cubic form but deeper than it is wide. Also there is A cube is normally fine, but still, there are zoning restrictions and the engineering standards by which to abide. With ROHN they come right out and give you the specs. Disclaimer: Do not use my calculations for anything other than an examples. Refer to the specific pages in the ROHN catalog for actual requirements. Going over the catalog they list the base for a free standing ROHN 45-G as requiring 4.1 yards of concrete. That makes the assumption the builder will strictly adherer to the ROHN Specs and maximum wind loading. Based on the 45 G specs the concrete base will be 5'3" on a side, or for a ball park figure that is 27.5 sq ft. A cubic yard is 3 X 3 X 3 or 27 cubic feet. Sooo... we can figure *roughly* with a base of those dimensions, each foot of depth equals one yard of concrete. Then the base would be 4 feet deep and 5' 3" square. BUT the 45 G is limited to only 11.4 sq ft of wind load at 45 feet when free standing with a 70 MPH wind limitation and no ice. (certainly they do have a healthy safety factor built into those calculations. Using the same calculations for a 65-G results in 8.9 cubic yards of concrete and *roughly* 65 feet for an 11 sq ft wind load at 70 MPH and no ice. This tower base is 7' 9" square, or 60 cubic feet for each foot of depth. That is 2.2 cubic yards. So, 8.0/2.2 surprise 4 feet deep again. It turns out, in my guyed installation I also happened to have about 9 yards of concrete. 1.5 yards at the base and the rest evenly divided between the guy anchors. I used slightly more concrete than required in the base. On thing emphasized by ROHN is there will be *no* welding of the reinforcements/rerod in the concrete. All the reinforcements are free floating. They have a whole set of specifications on those as well. all the rebar to install correctly and if it is like some Rohn tower there is a specification of some rocks and sand at the bottom of the hole. 6 inches of compacted sand and gravel for a drainage bed. There is also a specification as to the soil in the sides of the hole and requires soil samples to verify the soil is strong enough to meet their specs. Otherwise more concrete is required and I don't have the figures for that. Towers are not somthing youjust stick up and hope for the best. At least nothing more than a small TV antenna tower installation. This is probably the main reason the insurance companies don't want to see towers bracketed to the end of a house, or to the eves. My insurance carrier was willing to insure mine as long as there was no direct connection to the house. (coax doesn't count) Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
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