[TowerTalk] Tower buried section legs -- Buried in Concrete orBelow the Concrete?

[Grant Saviers]

Don,

"proper" is a poor choice of words.  Towers can be engineered either 
way, and there are pros and cons for each approach.  How the tower is 
loaded with antennas sometimes affects the base choice as well. As long 
as the design is within the allowable limits for the tower sections, 
there is no reason to expect the failures you cite.  You should know 
that there aren't "hole in the base plate" pier pin bases made for 65 
and that Rohn supplies buried bases for 25, 45, 55, and 65 at a fraction 
of the cost of pier pin solutions.

 From what I've seen and heard about tower failures, guyed towers almost 
always come down when a guy fails in some manner (turnbuckle, insulator, 
termination, guy corrosion, tree fall, vehicle contact, etc etc), not 
sheared bolts or fatigue failures.

I'm confident the PE did a great job for my buried base 65 tower, it is 
a trivial structure compared to his day job.  It was erected and plumbed 
in about 5 hours, 142' and there wasn't a tapered section in the prior 
install.

see http://www.publicsurplus.com/sms/auction/view?auc=1537335 for a 
commercial 160' tower for sale, not pier pin.

Grant KZ1W


On 2/8/2016 11:19 AM, Donald Chester wrote:
> I can't understand why so many hams build towers this way, especially a former AM BCB tower. The proper way to erect a guyed tower, particularly one more than about
> 50' tall, is to attach a flat base plate to the bottom of the tower.  The base plate has a hole at the centre of the triangle formed by the tower legs.  A galvanised steel pier pin is embedded in the concrete base pier, and extends up 4" to 6" above the surface of the concrete.  The first tower section is merely set on top of the concrete, with the pier pin sticking up through the hole, held vertical with a set of  temporary guys that remain in place until the first permanent set of guys is attached  That way, the tower is free to rock and sway back and forth on the concrete, and maybe even rotate, in heavy wind gusts.  This puts far less stress on the structure of tower sections. With a rigidly attached bottom section buried in the concrete, any motion caused by winds causes bending and twisting of the tower structure. This unnecessary stress can eventually cause weld failures and even shear bolts.
>
> Another plus, the base plate alleviates the necessity to absolutely perfectly plumb the bottom section before stacking the rest of the tower. After the job is finished, the tower can be fine-plumbed by adjusting the guy wires, without permanently stressing the tower.
>
> Temporarily guying the bottom section and plumbing it to the best of one's ability before stacking the rest of the tower sections is certainly easier and less critical that trying to get the bottom section PERFECTLY plumb in the concrete (temporary guys still required) before proceeding.
>
> With a substantial communications or broadcast tower, the bottom section was probably tapered to a point to begin with, making it unnecessary to even purchase or construct a base plate, and the pointed end allows even more freedom of movement with winds and guy wire adjustments.
>
> How many large commercial towers have you even seen with the bottom section buried in concrete?
>
>
> Don k4kyv
>
>
> Mon Feb 1 10:54:50 EST 2016
> Grant Saviers grants2 at pacbell.net wrote:
>
>> Interesting.  My R65 is 15+ years old, former AM BCB
>> tower, 20 foot
>> sections.
>> Grant KZ1W
> On 1/30/2016 19:46 PM, john at kk9a.com wrote:
>> There are no weep holes in my Rohn 65G.
>>
>> John KK9A
>>
>> To:	Dan Cisson<n4gnr at windstream.net>,	'Patrick Greenlee'
>> <patrick_g at windstream.net>,towertalk at contesting.com
>> Subject:	Re: [TowerTalk] [Bulk] Re: Tower buried section legs --
>> Buried in Concrete orBelow the Concrete?
>> From:	Grant Saviers<grants2 at pacbell.net>
>> Date:	Fri, 29 Jan 2016 11:12:06 -0800
>>
>>
>> FYI, Rohn 65 with 4 bolt 5/8" thick flanges on each leg has one 1/4" weep
>> hole on each leg, at both ends right next to the flange. The flanges are
>> drilled to the leg od and welded outside and inside to the tube before
>> galvanizing. So there are redundant paths for water to escape. My PE
>> specified 1 foot of 3/4 gravel for the legs to be set into before the 4x4x2'
>> base pad was poured.
>>
>>
>> Grant KZ1W
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