[TowerTalk] Screw Anchor Experience

[Jim Thomson]

Date: Tue, 18 Jun 2013 23:37:35 -0400
From: "Mark Robinson" <markrob at mindspring.com>
To: "K0DAN" <k0dan at comcast.net>, "Randy" <randy at verizon.net>
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Screw Anchor Experience

There was an article about this in QST a while back. I  followed the article 
and installed Magnesium sacrificial anodes to protect my buried guy anchors 
from corrosion.

Mark N1UK

##  why mess with screw in anchors ?  Only power company’s + telco’s use em. Even then
they use eggs in the EHS guys.   A  40’ tall utlility pole is already 6 feet into the ground. No
anodes used. 

##  The rohn type rod anchors are in contact with the soil, where it is trenched, so that portion
of the rod needs to be coated with roofing tar pitch.  Those GAC series anchor rods involve
excavating a huge hole, that is then trenched.  The concrete slab needs to be poured, then the 
entire mess is bakfilled with dirt. 

## A better way is to use elevated anchors. Six to ten inch diam steel pipe is used.   Weld a 
steel plate onto the bottom of the pipe.  Then weld  3-4 rocket fins onto the base.  Pour
a  layer of crushed gravel onto the base of the hole, then drop in the  steel tube.  A .375 inch
to .5 inch thick steel rectangular plate, typ  4-6 inchs wide x  12-14 inchs tall is welded to the
side of the steel pipe.   Typ  4-5 feet  above ground level.   Fill the hole with  re-enforced 
concrete and rebar.  And  don’t forget to fill the INSIDES of the steel pipe with concrete as well !! 

##  I designed  the above guy anchor bases for a buddy with a 190 foot tall  rotating tower  + 14
yagis.  He used  10 inch diam steel pipe,  sched 40.   Then had it all hot dip galvanized..after
all the welding was done.   It uses a fair amount of concrete for the 3 x holes.   Flip side is
it’s a fast install  vs  installing  a slab of concrete at the bottom of a hole, trenching the hole, and
using anchor rods, then backfilling.  .375 inch fiberglass guy rod used for the 12 x guys...with the
bottom 20 feet using EHS. 

##  If EHS used for guys...along with egg insulators,  dunno if the  last little bit of each guy
needs to be grounded or not.   The base of the tower is grounded, and the eggs have insulated
the EHS steel guy cable, so grounding the last bit of guy wire is not really doing anything. 

later... Jim   VE7RF