[TowerTalk] More crank-up questions

[Grant Saviers]

Contrary to other advice, do ground the tower anchor bolts to the 
rebar.   Then you have a great Ufer ground, considering the area of the 
concrete in contact with the earth.  The rebar should be tied per code, 
with sufficient overlaps and inside the concrete envelope per code.  
Depending on your site and storm patterns, additional ground rods may be 
appropriate.

For my two HDX589's we mounted the anchor bolts tightly to the base 
plate and tack welded rebar between the six bolts to make a solid sub 
frame so that the bolts wouldn't move when the concrete was placed and 
vibrated.  That way the concrete can be placed and finished without the 
interference from the base plate. This sub frame was wire tied to the 
main rebar cage.  After the concrete hardened the base frame was 
installed and leveled.  You can order stronger concrete (4000psi or 
higher) than the UST spec (2500) for a very slight up-charge.  The 
limiting factor in concrete for towers is tensile strength, not 
compression, considering the tensile/compressive strength ratio.  A free 
standing tower has opposite forces in the legs, 1 or 2 in tension and 
the others in compression when the wind blows hard.

Proper water content and curing is important.  You can get a slump test 
and post cure strength report from an independent testing outfit.  Code 
required this for my towers and I think it cost about $250 per tower, as 
they were poured on different days.

The 589 is positive pull down, but it doesn't matter vs the HD70 since 
for either design the tower weight is always on a cable, unless down and 
blocked for climbing.  Better to avoid that anyway and use a ladder or 
rent a boom lift.

The NF7P coax standoffs work well for me - the loop types not the "holds 
coax off the ground" type.

Grant KZ1W

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