That's going to be a very neat tower! I like the design...

Here's a possibly easier and maybe safer suggestion - if you're just looking to find the buckling strength, you could support the tower in a horizontal orientation (like on strong sawhorses or something similar) at each end.

Then put a couple of empty barrels on top, in the center of the tower. Add measured amounts of water to the barrels until she buckles. Water is 1 kilogram per liter (or 8.34 pounds per gallon). So if you had a 50 gallon drum full it would put 417 pounds plus the weight of the barrel on it. Two or three barrels would probably do it. Or if you had an old oil furnace tank...

At least when it fails, the most danger will be from having a barrel land on you, or getting wet!

Good luck and keep us posted!