I am designing a Gin Pole to lift a 500# load. The pole will be hollow Aluminum tube 24'x3"x3" and .125" wall thickness pinned at both ends. The pole will be at a 45 degree with the top secured with a horizontal 1/8" steel cable secured to a tree. Thus vertical load cable and the horizontal support cable to the tree will be at right angle putting a pure compression load on the pole of 700#. Will the Aluminum tube describe safely withstand such a compressive force in column without buckling ? If not is a a heavier wall thickness prescribed?
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$\begingroup$ Are you sure of "pure" compression? the mounting will be perfectly centred so as to not cause any side load? $\endgroup$– Solar MikeCommented Oct 17, 2022 at 18:16
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$\begingroup$ Thanks Solar Mike $\endgroup$– David NagyCommented Oct 18, 2022 at 23:05
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Euler buckling equation is{
$Pcr = \dfrac{\pi^2EI}{le^2}$
for 3x3x1/8 aluminimun tube,
$E = 10x10^6 psi, I = 1.78 in^4$
for a column with pinned ends, K = 1.0, conservatively use 1.2,
$Le = K*L = 1.2*24*12 = 346 in$
$Pcr = \dfrac{\pi^2*10^7*1.78}{346^2} = 1467 lbs > 500 lbs$
Yes, strengthwise it would work provided the end condiditions are as assumed, and there is only compressive stress on the pole. But instability caused by flexibility could cause problems.
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$\begingroup$ Thanks, I couldn't get my diagram to display, and even with the 1.2 safety factor it's 2x the expected load. $\endgroup$ Commented Oct 18, 2022 at 23:18
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$\begingroup$ 1.2 safety factor is for the potential defects in the material/tube. you shall watch out for incidental eccentricity which can introduce a bending moment. Otherwise, it will be fine under the load. $\endgroup$– r13Commented Oct 19, 2022 at 14:08