# In Column Bucking strength of 24' 3"x3" Hollow Aluminum Tube with .125" Wall thickness

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?

• Are you sure of "pure" compression? the mounting will be perfectly centred so as to not cause any side load? Oct 17, 2022 at 18:16
• Thanks Solar Mike Oct 18, 2022 at 23:05

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.

• Thanks, I couldn't get my diagram to display, and even with the 1.2 safety factor it's 2x the expected load. Oct 18, 2022 at 23:18
• 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.
– r13
Oct 19, 2022 at 14:08