Bases have gotten bigger. Crankup mounting plates have much heavier
steel and angles rather than plates. The catalogs show much less
concrete than the actual wet stamped drawings I have for my HDX589 UST
freestanding. An owner of an earlier 589 told me his base is much
lighter, but I haven't had a chance to measure it. The lattice pitch on
the 589 also varies, more strength where they overlap. I'm not sure
this was always so, the Tri-Ex 354 I have is constant pitch of bracing.
Why? One significant reason is the "upsizing" of the wind speed
specifications as standards were revised. Other reasons could be better
structural analysis which no longer needs a Cray supercomputer, or
liability/insurance concerns.
Grant KZ1W
On 5/13/2011 5:18 AM, WA8JXM wrote:
> 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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