At 12:19 PM 6/26/2007, Clint Talmadge wrote:
>Bob, AD5VJ asked a question about a concrete base for a Rohn tower.
>When Bob, NA6T posted this reply I thought the amount of concrete
>sounded a bit high. I checked the Radian site and sure enough that
>is what is listed. So I drug out my old Peoria Rohn Catalog, circa
>1983 and researched base dimensions. Peoria Rohn specs call for a 2'
>X 2' by 4' deep hole for the tower that Bob, AD5VJ is installing. It
>calls for guy anchors of 2' X 2' by 1' deep.
>Which raises the question: Did Radian re-engineer the base
>dimensions or did the fear of litigation cause Radian to up the numbers?
Purely speculation, but a lot has changed in the last 25 years,
including how windspeeds are specified (or, more properly, what load
corresponds to what rated speed), perhaps some assumptions about the
bearing capacity of soil, perhaps standard construction practices have changed?
One likes to hope that folks aren't motivated by "fear of litigation"
but, rather, a desire to "do the job right", and if a reanalysis
shows you need different dimensions, then so be it. I sort of doubt
they just blindly increased the size in hopes that it would be "safer".
>I've installed two towers for myself, both Rohn 25G, both in the 30'
>to 40' range ( I use a full section for the base) and both were
>planted in 2' X 2' X 4' holes. Neither came down (yet).
That's not surprising on a sample of 2. The footing design would
generally not be designed to fail at 1 mi/hr over the limit, but
would include some margin for things like variations in soil,
variations in material properties, etc. Failure is a probability
thing, not a "exceed the limit and total destruction is certain" sort of thing.
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