box tube strength

huangyhg

box tube strength
looking for the amount of weight for a 2x2x1/4 box tube 20' long vertical with a 3'x2x2x1/4 box extension on top and base is 12" 2x2x1/4 box with 6x6 gusset on 2 sides of top extension and base, noticed alot of flex in the tubing because of the length but was wandering how much would it hold before bending or breaking ??
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i would look at buckling of the column as the first failure mode. treat it as a complete column first and use euler's formulae to give you the buckling load.
tube 2x2x1/4 is very slender member for the 20 foot height. i would never use suck a slender   
i agree w/ corus and lutfi - 2x2 and 20' in height? even it would carry the load w/o failure, the servicibility of it will be a problem.  the deflection would be huge and the vibration (bouncing) will be a problem as well.
anyway, if you are to use it, here;s a list of limit states whati think you should check:
(1) local buckling of plates in the tube, i.e. b/t ratio
(2) overall column buckling