Maximum bending moment is proportional to the
difference between the cubes of the O.D. and I.D.
An approximation to this is that for constant wall
thickness, max moment scales as the square of the
diameter. Thus 4 inch tubing should be four times
as strong as 2 inch, for the same wall; it's
actually more than 4 times as strong, since that
was only an approximation.
OTOH, stiffness, is proportional to the
difference between the fourth powers of the O.D.
and I.D. A similar approximation can be made
whereby for constant wall thickness, stiffness
goes as the cube of the diameter. Thus 4 inch
tubing is at least 8 times as stiff as 2 inch
for the same wall.
This is why 4 inch irrigation tubing is so much
easier to erect than 2 inch 6061.
Rick N6RK
richard@karlquist.com
www.karlquist.com
N4KG said:
>Remember, maximum bending moment of a thin cylinder
>goes up as the 4th power of the diameter so a 2 inch diameter
>section will be 16 times stronger than a 1 inch diameter section.
>A double walled section will be less than twice as strong as
>a single walled section of equal wall thickness.
Tom N4KG
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