Did you look at the Rohn technical prints to determine the depth of the concrete?
I am putting up a Trylon SSV tower and they have the specs on their website if you need another one to compare with. trylon dot com, Self supporting. They had a tapered bottom about 18" tall then the square top part. My experience with drilled cassons (large building construction) is that the bell portion adds extra strength to the base which acts as a footing. You could dig the ground out square at the bottom, pour a footing usually 24" thick, depending upon the soil, then build your form, then pour the column portion of the concrete. Strip the forms a few days later, then slowly back fill while tamping the ground down to meet compaction specs, then fill a little more to meet compaction specs, then you have a tower base that should not go anywhere. I just poured a tower base on a mountain top and I used more concrete than was speced, plus I poured it rather stiff, and the extra was poured around the base to make the tower top stronger. Tower bases bigger is better. Good luck with your project. Butch, KE7FEL/r To: Repeater-Builder@yahoogroups.com From: mafl...@att.net Date: Sun, 13 Sep 2009 15:42:46 +0000 Subject: [Repeater-Builder] Tower Foundations One of my family members is putting up a tower to support his business radio (farm) , the family GMRS repeater, and a fairly large microwave dish to obtain internet. The choice so far is a Rohn SSV compromised of the following sections: 10NH, 9NH, 8N, 7N, and 6N. Here the question: The local PE who approved the prints suggested using drilled belled foundations. This nearly doubles the cost of each foundation in terms of drilling and concrete. Typically how much additional resistance to overturning motion do they add above straight sided holes?
