[TowerTalk] BASE REBAR and Lightning

[Jim Lux]

Michael Tope wrote:
> ----- Original Message ----- 
> From: "Jim Lux" <jimlux at earthlink.net>
> To: <mecker at peoplepc.com>
> Cc: <towertalk at contesting.com>
> Sent: Friday, October 05, 2007 6:54 AM
> Subject: Re: [TowerTalk] BASE REBAR and Lightning
> 
> 
>> mecker at peoplepc.com wrote:
>>> Read that base rebar (which must be electrically tied together)
>>> should be internal min of 4 inches from edge of concrete base.
>> That's so the rebar doesn't protrude from the surface of the concrete, 
>> providing a capillary gap (between concrete and rebar) for water to 
>> infiltrate.
>>
>>> Here's my question. (Im learning disabled...etc..etc.)
>>>
>>> What about guys that use a piece of rohn 25 as the base, stick
>>> the end in the 6 inches of gravel, and then fill up the rest
>>> with concrete. There is no 4 inches of insulation with the earth
>>> there, because the gravel has gaps  and moisture in it
>>> which connect with the earth anyway. (a chemical fact)
>> Those guys aren't following standard concrete practice (avoiding things 
>> sticking through the concrete/soil interface)
>>
> 
> That is the standard procedure if you put the bottom section of 
> Rohn 25 in the concrete base. The idea is to plant the bottom of the 
> tower legs in the gravel so that they won't fill up with water over time 
> (this assumes your water table is lower than the bottom of the leg). 
> Hence the conflict with the prescription to keep metal away from the 
> concrete-soil interface. If you use J-bolts and a flat bottom base, this 
> conflict in requirements is avoided, although if you really wanted to
> I suppose you could put PVC extenders on the bottom of the tower 
> legs  in former case so that the metal stayed inside the concrete 
> envelope :-)
> 
> 73, Mike W4EF..................................................

Or, why one might want to use a pier pin base?