I've encountered a problem that I can't seem to solve. I designed a column with a diameter of 4 m and a height of 20 m, with a wall thickness of 1 mm, and the only load is gravity. The deflection of the top cover (membrane) is 58 mm :) .
The column itself does not deform. The material is PVC tarpaulin.

How can such a structure support 256 kg?

I design inflatable structures, but I did not add internal pressure to this calculation.

Does anyone have any thoughts on this?