On Fri, 02 Aug 2002 Chris BONDE <ve7hcb@rac.ca> writes:
> However, your tower has guys that causes a push via a pull down onto
> the concrete base. The guying changes the movements and momentums
> (momenti?). (VE7HCB)
N4KG: Ideally, the Guys LIMIT movements of the tower :-).
Maybe, in the case of a mast or a tower with no guys
> the base offers a change in centre of gravity.
Yes, but that is NOT the primary contributor to keeping a self supporting
tower up. Picture a tower attached to a block of concrete ABOVE ground.
How much bigger would that block of concrete have to be to keep the
tower from blowing over. THAT would relate better to your idea of the
contribution of a low center of gravity. And even then, the SIZE and
SHAPE of the BASE are significant factors in the load carrying capability
of the pole / mast / tower. N4KG
As I said before, the EARTH holds up the tower. The BASE only
provides an adequate coupling to the earth. That coupling requirement
is quite different for self supporting vs guyed towers. Center of
gravity
is NOT the critical item. N4KG
I recommend you read up on the subject of STATICS in a college
Physics or Mechanical Engineering Text. Then perhaps something
on the holding capability of soils in a Civil Engineering Text. Then
perhaps you will have a better perspective on the contributions of
each component to the whole picture. I guarantee you, center of
gravity is virtually insignificant compared with the others. N4KG
>
> I have been trying to obtain a concensus on the depth of a mast,
> power pole etc for the heigth. If just put into the ground, if a
heavy
> base is used then things change.
>The best appears to be, One foot plus 10% of
> the complete pole must be under the ground. (VE7HCB)
N4KG: That is the rule of thumb for (wooden) power POLES
(with almost NO load at the TOP)
A steel pole with a concrete base is a whole different
matter and MUCH more complex, depending on the
size and shape of the concrete block, the characteristics
of the soil, and the size and shape of any load on TOP
(such as antennas).
>
> Chris opr VE7HCB
>
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