For a simple bending-resistant frame, I obtain very large deformations.
What is the reason for this?
The problem is that a very large value was specified for the cross-section properties for surface Axial A.
For the desired stiffness of the cross-sections, the values probably don’t need to be too great. Try smaller values.
Check also whether the sums of the loading and support reactions are equal.
When specifying such large values for complex models, numerical problems canaries when solving the equation system.
The automatic calculation of the self-weight is done by means of the density of the material and the surface Axial A of the cross-section.
In your example, you obtain very great loads because of the large cross-section surface.
You can either change the value for Axial A, clear the selection of the self-weight in the "General" subtab of the load case, or change the material thickness to 0.00.