I am planning to re-work (enlarge) my concrete base to support a greater over-
turning moment for a self-supporting tower. I have been looking at a lot of
tower base designs trying to figure out how deep the anchor bolts should be in
the concrete in order to have enough pull-out strength (50,000 lbs). They seem
to be all over the map.
The US tower design appears to use about 5 ft long 'J' bolts, as did my
current Heights tower. A large Andrew Earth Station Dish bolts are only 18"
deep for about the same OTM. The Hilti epoxy design is also about 18" for a
1.25" bolt (which has only about 30,000 lbs working, 110,000 lbs Ultimate, in
2000 psi concrete).
The reason I am asking is this will govern how much of the old base has to be
removed to allow a good installation over it. (For various reasons the tower
position cannot be moved much.)
This is only for planning info, I will have a PE certify the final design.
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