On 11/30/2013 8:10 PM, Grant Saviers wrote:
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,
Recent, commercial rebar cages ordered with the towers have come through
welded instead of tied.
I have the wire, but it's a whale of a lot easier to weld it. If it's
good enough for the manufacturer, then it's good enough for me.
73
Roger (K8RI)
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
snip..
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