Denis, can you describe what you are trying to model? Do you have a picture of the real parts maybe? That could help a great deal.
Although the thread title says "two simple supports", in the diagram you show (which is the classic diagram for a simply-supported beam) the constraints are different at each end.
The left-hand end is constrained in Tx and Ty (and in 3D, Tz as well).
The right-hand end is constrained in Ty (and Tz) but is free in Tx.
If you create these constraints in your model, does it give the answer you are looking for?
Thank you for your very specific answers.
Actually I have not chosen the right design for my question.
It is a simply supported beam laid plans without restraint.
See the attached drawing.
The same constraints would be appropriate, even so.
To ensure 'necessary and sufficient' constraint, we assume that one end will slide and the other end will remain fixed.