Re: ATM Balsa Wood

["David J. File" <davefile@compuserve.com>]

The engineer responds...

    There are usually two ways to think  1) Local and 2) Global.  The
"longitudinal" stiffness is a "global" and the wall thickness is a "local".
 Usually the "fibers" farthest from the "neutral axis" carry the load.  
For a tube the neutral axis runs down the center.   That's why at tube is
about as strong but much lighter than a solid rod, because the center
doesn't really do much, it's neutral.
    The next benefit can be had by taking the "solid walled tube" and
converting in to a "hollow walled tube".  Of course we really can't do this
or we just have two tubes, one inside the other,  Ha!  So we add just
enough "core" and just strong enough to handle the "worst case" loads that
our tube will see and wha-laa ... we have a just about the lightest tube we
can get.

Regards,
Dave File