[TowerTalk] tower base concrete or not

[Al Williams]

I dunno?  My "intuition" sez:

----- Original Message -----
From: "Tower (K8RI)" <tower at rogerhalstead.com>

> The concrete only does three things at the base of the tower.

> It keeps it  from sinking,
  Then why do the manufacturers specify the hole at  about twice as deep
as it is wide?

>It adds area to keep the base from shifting, or moving,
   Do you mean sidewall area? Lateral shifting and moving--or tipping?

> it > protects the tower base (if properly done). It doesn't take a
lot.
  ok

>  (It does  not prevent the tower from tipping over). To do that takes
a pretty good > chunk of concrete and a very strong tower.)
  It was said during construction of Seattle's space needle's that
enough concrete was used at the base to place the center of gravity of
the   needle (and concrete) below ground.  I think that the concrete
specified by tower manufacturers may (?) also place the center of
gravity below ground.  At least having the hole deeper than wide helps
in that respect.

Granted, "intuition is no substitute for stress analysis.  Only one of
my four tower stress analysis calculations includes foundation
calculations. As a retired electronics engineer, I cannot follow the
analysis which uses so many undefined symbols.  However the analysis
does include the following note "Foundation has been designed to
accommodate the following loads; Overturning Moment, Base Shear, and
Structure Weight".

Does the overturning moment mean tipping?

k7puc