Ken,
I just put in a base for a HDBX-48 on Wednesday. Several people
here on the list thought the 5 yards of concrete specified by Rohn was not
enough and the rebar specified by Rohn was completely in adequate. Most of
the local old timers thought I was putting in crazy too much concrete, as
their towers had been put in with at most 3 yards and had been up for years.
One local in particular whom I know has put up many towers (all of which are
still up) advised me all that was really needed a little under 2 yards of
concrete. I respect this guy because I know for a fact he has been there
and done that. It was kind of difficult to go against years of local
experience and wisdom, but in the end I chose to follow the prime directive.
At $93 per cubic yard is was not an easy decision to make on my budget. I
was able to save some $ by hand digging the hole myself the day before,
which was a lot of work for a fat aging man.
The strange thing is Rohn sells or at least used to sell a cylinder
"dirt" base for these towers that has/had a very small volume. I suspect
the true answer is a little of both. The old numbers were used to sell
towers - look how easy this is, and you only need to a 2 yards of concrete!
The new numbers are driven by liability.
73,
Joe kk0sd
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of WA8JXM
Sent: Friday, May 13, 2011 7:18 AM
To: towertalk@contesting.com
Subject: [TowerTalk] concrete bases for freestanding towers
Many years ago I had a 64' freestanding tower with a 3el triband beam
(TA-33) on it. The base was only 2 cu yards of concrete. As far as I
remember, that was all the manufacturer (Heights) recommended at the time.
Now when I look at anyone's recommendations, the base requirements are much
larger. Rohn (and others) recommends 3 cu yards even for a 40' BX tower.
I had used only 1 cu yard for a freestanding 40' tower.
Is my memory faulty, or have the recommended bases grown over the years?
Were the old recommendations inadequate, or has everyone grown super
conservative over the years? "If one yard is adequate, three will be
better, so let's use five yards"???
As one ham commented on the air yesterday, the only failures he has ever
heard of were in the tower itself, not the base falling over.
Ken
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