If you have good soil, good guy anchors, and zoning isn't a problem a dirt
base works just fine with a 40 foot tower. ROHN even used to make one. As an
educated guess, I'd say that only about one out of ten towers around here of
60 feet or less has any concrete in the base. Mine has several yards while
the guy anchors are 4 X 4 X 5' deep.
73
Roger (K8RI)
>I think they changed the windload from 75 mph to 90 mph.
>
> 73, Dick, W1KSZ
>
> Jim Lux wrote:
>> 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.
>>
>> Jim, W6RMK
>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
> --
> 73, Dick, W1KSZ
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|