shells weight in sap2000

[farzad1366]

Dear all
i've been modeled a vertical cylindrical shape in sap2000 by using shell/layered, defined material weights per unit volume,run the simple analysis.
when i checked the outputs i noticed that the Fz in display-show tables which it is the dead load, it's 1/3 of the actual effect with the calculations i've made by hand. what is wrong?
how i could be sure about the weight of the structure?

 

[BeFEA]

1. check the level of approximation of flat shells with your theoretical cylinder;
2. check the unit weight of each of the materials assigned to the shell layers;
3. check the thickness of each layer of your layered shell. There might be sth wrong there.