Hi Diego,
You need to know the yield strength for the steel used to make the tank. Then you can add the Structural Steel NL from the General Non-linear Materials library and edit the value of Yield Strength in that generic example and use the specific value for the steel used to make the tank.
If the upper edge of the tank is connected to a roof structure, it would be more accurate to include the roof structure in the model because the roof has some amount of flexibility while the displacement support provides no flexibility. This may change the stress in the tank walls slightly.
You are navigating away from the AIS Discovery experience