On Thu, 01 Aug 2002 Chris BONDE <firstname.lastname@example.org> writes:
> I thought that the concrete was mainly to lower the centre of
> gravity for the complete antenna structure (VE7HCB)
N4KG: WRONG ! Center of gravity has NOTHING to do with
resisting overturning forces in a GUYED tower (and
only contritubes partially in a self supporting tower).
My (guyed) towers are set in the ground with NO concrete.
The center of gravity is pretty high but they have
been up for decades and withstood 90 MPH winds.
As stated previously, the purpose of a BASE is to
provide sufficient AREA to support the weight of
the tower plus the vertical forces from the guys.
The EARTH supports the tower.
The BASE spreads the load over
sufficient AREA to prevent it from sinking.
In areas where FREEZING occurs in winter,
the BOTTOM of the BASE must be BELOW
the FREEZE LINE to prevent the base from
pushing UP on the tower which adds to the
tension in the guys.
For self supporting towers, the BASE 'couples'
to the earth to prevent sinking AND overturning.
> This is the bases of the three legged cow milking stool. (VE7HCB)
N4KG: I believe you mean BASIS and not "bases".
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