[TowerTalk] Screw Anchor Experience

[K8RI]

On 6/18/2013 9:13 PM, Dick Green WC1M wrote:
> Any anchor that's exposed to soil is at risk of corrosion. Anchors sunk in concrete are just as vulnerable because typically a good portion of the anchor rod is not in
  the concrete -- it's in contract with soil above the concrete footing. 
For example, Rohn spec calls for my anchor footings to be poured in a 
6-foot long by 3-foot wide
hole that's 4-feet deep. The concrete footings are only 18" deep, so 
there's about 2.5 feet of soil that the anchor rod is in contact with. 
Since the rod is set at an angle,
probably 3-4 feet of the rod is in contact with soil above the footing.
>
> The Rohn concrete anchor rods are very heavy duty, but just in case I slathered several coats of roofing tar on the portions of the rod that were above the concrete block.
>
> Regardless of the type of anchor rod you have, it's a really good idea to inspect them every few years. That means digging down a bit to see if there's corrosion.
>

I think Dick makes some good points.
All the anchors here are 6" heavy wall pipe set in 4' of concrete
I went with elevated guys which I do not recommend unless you have no 
choice, but I had to clear a driveway.

After 11 years the anchors (which are only painted) show no sign of rust.

But a lot depends on the type of soil. That and I am using non 
conducting guys

The power company uses screw anchors, but I think they are between 6 and 
10 inches across with a 1 or 1.25" shaft.

73

Roger (K8RI)



> 73, Dick WC1M
><snip>