Masts and stacking considerations

[Stan Griffiths]

>K7LXC@aol.com 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: barry@w2up.wells.com
>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.

stan  w7ni@teleport.com