On 1/2/14 7:41 PM, W7ZZ wrote:
I'll add my experience, for what it may be worth. A number of years ago,
I purchased two new AN Wireless freestanding towers, an HD70 and a
LD60. The HD70 requires a foundation that is 10'x10'x5' and the 60
footer requires a foundation 7x7x5. I had the holes dug by my
landscaping contractor (the house was a custom and was under
construction at the time). However, by the time I started getting the
bids more than a year later, one hole had sloughed a bit and so some of
the bidders put in some amount for excavation work.
Bids for whatever excavation work needed tobe done, fabricating the
rebar cage, hiring the concrete pump truck or line pumper (the holes are
not otherwise accessible due to their location), the concrete and the
labor to do the job ranged from a low of $9,000 or so to a high of
$16,000, I think it was (gee, I didn't keep a copy of that one). One
contractor was kind enough to explain why: The pump truck or line
pumper was $1,000 (every contractor told me that; one had his own line
pumper so that cost was built in); depending on when I got the bid (this
went on over several years), the cost of the concrete was $85-110/yard
(at the time, I was told there was a shortage of concretedue to some
massive dam construction going on in China, sucking it all up);
yeah, three gorges dam.. kind of like Hoover/Boulder Dam on a larger
scale.. Amazing to think of a single construction project having an
impact on the global supply of cement.
approximately one tonof rebar would be needed for the two foundation
rebar cages. The contractor's men would have to carry that rebar from
the front of the house, where it would be dropped off by the fabricator,
to the two holes, a distance of 100 feet or so for the big tower and 300
That's a huge bump in labor.. schlepping the rebar by hand is a huge
amount of work. Probably not to bad if you're doing it yourself and
dragging one or two bars a day for a month.
feet or so for the smaller. Labor in each case turned out to be about
1/3 of the bid or less and every contractor told me it was a several day
job. Every contractor expressed concern about the need for the buried
tower stub to be perfectly level (so that, when attached to it, the
tower wouldn't lean).
This is why commercial installations of traffic lights, signs, etc. have
a bunch of big threaded bolts sticking up, and you run the nuts up and
down to make a level surface, install the above ground part, and install
the top nuts.
I don't know if this is a viable strategy for ham towers with 3
relatively small diameter bolts. In this approach, the bolt part above
ground takes a fair compression load, and you need to make sure it's not
going to buckle. The street lights, traffic signal kind of
installations around here have 8 bolts that are 1" plus in diameter in a
12-18" circle.
One potential bidder told me after eyeballing the
site, seeing the foundation plans, etc., that he didn't want the job.
The moral of the story is that,at least for a freestanding tower
designed for big wind loads, the cost of the tower is just the tip of
the iceberg. The foundation work and the boom truck needed to get the
towers up in the air is a major expense. I've lived in the house for 5
1/2 years now. My towers consist of two very large holes in my back yard.
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