Since I will be mechanically and electrically bonding three horizontal
radial cast beams to the tower's rebar cage at one end and likewise at
the other end to piers in the ground with rebar in them (Ufer grounds,
see below) I may not need to put copper straps onto the tower base,
tower, or tilt accessory. Instead I would be driving an 8ft copper clad
ground rod between each of the piers. The piers are on 14 foot
centers. I would be connecting the rods to the (Ufer ground) piers with
wide copper strap, heavy gauge copper wire, or I might use 1/4 inch ID
copper tubing or thereabouts to run between The Ufer grounds and ground
rods.
My Ufer grounds: Each of the three Ufer grounds consists of three each
12 inch diameter rebar reinforced piers connected to each other by a
18 inch high 24 inch wide 7 ft long rectangular block of steel
reinforced concrete. All the rebar in each set of three piers is bonded
together and is electrically accessible by way of a steel tube
protruding out of the top of each group of three piers.
Additional mechanical integrity beyond that called out by the MFG:
The MFG asked me to pick one of two foundation designs: 1. a 5 ft
diameter 8 ft deep hole or 2. a 4x4x8 ft hole where the 8 is depth. The
best estimate I got for drilling the round hole was $1030 and some
liability for teeth on the drill etc. I have estimates ranging from
$300 to $500 for the square hole. The square hole may end up 4x? at
the surface to get a 4x4 dimension at the bottom of the hole. Some
operators say they would have one sloping side making the top of the
hole 4x8. Others say maybe 4x6 at the top and yet another says he can
do 4x4 from the surface down 8 ft. The reality may be somewhere in
between but at over $100 per yard of delivered mud things could get
expensive if the hole grows much.
The concrete is to be poured against undisturbed earth so forming and
backfilling to reduce the requirement for extra concrete at the sloping
side is not in compliance with the written specs from the MFG.
The central foundation (MFG's rebar cage) will be tied into three
radial cast in place rebar reinforced beams that are each terminated at
the three outlying Ufer grounds for additional strength holding the
tower upright. The width and depth of these beams as well as their rebar
schedule has not been finalized. Also the attachment of the beams to
the outlying piers has not been finalized but will likely be one of two
ways.
1. drilll and dowel into the outlying foundations or 2. Use anchor bolts
set into drilled holes to attach a vertical piece of steel channel with
holes in its flanges. Rebar with bent ends will be inserted into the
holes and bent some more to secure them during the pour.
All of the above will be done only if passed by my mechanical
engineering consultant, a good friend with MS Mech Eng from UCLA and 35+
years of hands on experience with steel structures (mainly a deep diving
research submarine and its various ancillary equipment.
I am soliciting suggestions for improvements, warnings, or whatever.
Please sanity check the above.
TIA for your consideration,
Patrick N5G
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