The principle behind prestressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.
Analysis-Compute stresses in steel and concrete when the form and size of the section are given or assumed, Design- Choice of a section out of many possible shapes and dimensions
A precise determination of stress losses in prestressed concrete members is a complicated problem because the rate of loss due to one factor, such as relaxation of tendons, is continually being altered by changes in stress due to other factors, such as creep of concrete
The deflection of a flexural member is calculated to satisfy a limit state of serviceability. Since a prestressed concrete member is smaller in depth than an equivalent reinforced concrete member, the deflection of a prestressed concrete member tends to be larger.
Reinforced concrete beams and slabs carry loads primarily by bending. They are, therefore, designed on the basis of limit state of collapse in flexure.
Shear failure, which in reality, occurs under the combined action of shearing forces & bending moments is characterized by very small deflection and lack of ductility.