From: Ross Sackett 
To: atm{at}shore.net
Reply-To: Ross Sackett 


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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