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Masts and stacking considerations

To: <>
Subject: Masts and stacking considerations
From: (Stan Griffiths)
Date: Sat, 15 Jun 1996 00:53:26 -0700 (PDT)
> writes:
>>     If you go to a rotator with a clamshell type of mast clamp, a 3 inch is
>> no problem because it'll self-center.  Correct me if I'm wrong, but going
>> from 2 inch to 3 inch isn't necessarily going to save you any money because
>> it doesn't significantly increase the strength of the mast.  Besides, the
>> forces remain the same.
>> >
>Steve - I believe you are wrong. I don't have the formula handy for 
>calculating tensile strength of a round member, but diameter is the 
>single-most important factor, as it is exponential, not linear. I have 
>the formula at home somewhere, and can dig it out, if there is interest, 
>and nobody else has it handy... 73 Barry
>Barry N. Kutner, W2UP       Internet:
>Newtown, PA                 Packet Radio: W2UP @ WB3JOE.#EPA.PA.USA.NA
>                            Packet Cluster: W2UP >WB2R (FRC)

I think the formula you are looking for is in my article on mast strength
that was published in NCJ a few years back.

Unfortunately, I have not been following this thread, but most of the time
people are interested in the bending strength of a mast with a stack on it
and not the tensile strength.  The bending strength of a mast is
proportional to the "yield strength" which is a function of the type of
metal and alloy the mast is made of.  It is also a function of the "moment
of inertia" of the mast which is determined by its shape, usually a round
cylindar, and the actual dimensions of the mast.  Ouside diameter is VERY
important to mast strength.  A three inch mast is a LOT stronger than a 2
inch mast, all else being equal.

BTW, "tensile strength" usually refers to how much "stretching" a member can
take like pulling on a rope or cable.  It is true that when bending a mast,
one side of the mast is in tension while the other side is in compression so
tensile strength alone does not give enough information to know the whole story.


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