Re: ATM 2 Piece Poles - and how trusses really work

[Ross Sackett <rsackett00@yahoo.com>]

A bit more off the top of my head, again.  

Up to loads where buckling is an issue the squashing
or extension of truss members in tension and
compression is controlled by the cross-sectional area
multiplied by the modulus of elasticity.  Since the
steel in the connector bolt has 3 times the elastic
modulus that the aluminum in the tube has, the bolt
need have only 1/3 the cross-sectional area to match
the stiffness of the tube in tension.  A 1 inch
diameter/0.049 wall thinkness aluminum tube has an
area of about 0.15 square inches.  One third of this
is 0.05 square inches, which is close to the
cross-sectional area of a 1/4 inch bolt (ignoring the
threads).  Thus, a 1/4 inch steel connector bolt is
the minimum for a 1 inch diameter aluminum tube.  Of
course, the connections between the bolt and the tubes
will have to be similarly stiff...

Have I gone wrong somewhere along the way here?

Ross






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