I have modeled a pole structure by member and then modeled the same structure by plate element. Now, how can I compare the flexural moment at certain height in two scenarios?

Lets compare the two scenarios.

I have modeled two structures of a pole/tube.

 (a) By member entity with the 2.00 m dia (from mid of the shell) and the height of 20 m. 

(b) By Plate entity with the similar 2.00 m dia (from mid of the shell) and the height of 20 m. 

I have simply applied the self weight acting along the lateral direction (X) for both the cases.

Now after analyzing I will compare the pole moment at the distance 9.556 m from the top .

For the model with member, the moment thus reported is 675 KN-m

Lets take second case ( the model with plates).

Open the model (attached).

Now, here we need to determine the total pole moment, so we need to find the total axial forces (tension+ compression acting about the neutral axis of the entire annular section).

In this model the center line is taken as (0, y, 0) .

So, we can find the moment contribution in one of the quadrant and then multiply with four for contribution from all the four quadrants ( as all the quadrants have symmetric compression or Tension forces).

If you switch on the plate orientation (SHIFT+T), we need to take the SY (membrane stress). Now convert it into force by multiplying with cross sectional area and then multiply with the lever arm distance.

So, for each element, the cross sectional area (A) is around 34700 mm^2 (347mm width* 100 mm thk.).

Now, please see the calculation below in the spreadsheet. The corresponding spreadsheet is attached herewith.

The total moment is 665 KN-m . If we perform finer meshing, we could get the value closer to 675 KN-m as reported by model with member entity.

Pole moment.xlsxTube_member.STDtube_plate.STD