What are the assumption on which the stress analysis developed in prestressed concrete structure element is based?

Assumptions on which the stress analysis developed in prestressed concrete structure element is based upon the following:

1. After the bending to the transverse plane section of the member will be a plane.
2. Hook’s law is applicable for steel components and concrete, to the limits of the deformation taking.
3. The length of reinforcement doesn’t get changed with the stress in the reinforcement.
4. Stress gets changed only for the concrete component.