K7NV did a computational study some years ago to compare pier pin versus fixed
base construction, and found some circumstances, IIRC, where the fixed base
would cause failure in the first section at a lower wind speed than if an ideal
pier pin were used. That said, my Rohn 25 pier pin is far from ideal, because
there is a lot of friction between the base plate and the top of the concrete
base. Since there will be maximum downward force at the times you're most
concerned about, you have to wonder how much of the advantage will be lost.
Oh by the way, I very much doubt my 97 foot tower is straight within a degree,
and I don't know where true North is within 5 degrees, even. Honestly, the
things some hams get spun up about!
73, Pete N4ZR
At 04:07 PM 8/29/2006, Chet Moore wrote:
>I'm with you Kieth,
>
>Don's statement certainly doesn't apply to all towers. Rohn 25 and 45 and
>AB-105 are some others it doesn't apply to.
>
>73
>
>Chet n6zo
>----- Original Message -----
>From: "Keith Dutson" <kdutson@sbcglobal.net>
>To: <towertalk@contesting.com>
>Sent: August 29, 2006 3:03 PM
>Subject: Re: [TowerTalk] Tower base
>
>
>> Te each his own. I have never put up a guyed tower using a base plate and
>> do not have any future plans for one. I always use the concreted short
>> tower section as recommended in the Rohn catalog. I have never had a
>> leveling problem so perhaps I cannot see from your perspective.
>>
>> 73, Keith NM5G
>>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com
>> [mailto:towertalk-bounces@contesting.com] On Behalf Of Donald Chester
>> Sent: Tuesday, August 29, 2006 1:02 AM
>> To: towertalk@contesting.com
>> Subject: Re: [TowerTalk] Tower base
>>
>> Absolutely the WORST possible way to build a guyed tower is to set the
>> bottom section in concrete. It is far better to use a base plate with a
>> pier pin in the concrete, to allow the tower base some freedom of movement
>> in heavy winds. The tower will tend to sway and twist in windstorms, but
>> if
>> the base is set in concrete, that puts an unnecessary amount of stress and
>> shear on the tower structure.
>>
>> Another problem is that it is nearly impossible to get the buried base
>> section absolutely plumb, no matter how carefully you measure. And
>> concrete foundations do settle with the passing of time, so with certain
>> soils, the tower may not stay plumb even if it was achieved initially.
>>
>> You very rarely see commercial tower installations built that way.
>>
>> Don, k4kyv
>>
>>
>> _______________________________________________
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