The stresses due to prestressing alone are generally combined stresses due to action of direct load and bending resulting from an eccentricity applied load, stresses in concrete are evaluated by using well known relationship for combined stresses, this type of attack in alloys is due to internal metallurgical structure, which is influenced by composition, heat treatment and mechanical processing.

The concept of pressure line is very useful in understanding load carrying mechanism of a prestressed concrete section, if a prestressed concrete member is cracked, it behaves similar to that of a reinforced concrete section, in contrast to direct method of analysis of resultant stresses at a section of a prestressed concrete beam outlined pressure or thrust line concept can also be used to evaluate stresses.

These compressive stresses are balanced by tensile stresses developed due to transverse loads on beam, so that resultant stress at bottom fiber is zero, a furr increase in loading results in development of tensile stresses at soffit of beam.

When beam supports uniformly distributed load, corresponding tendon should follow a parabolic profile, when a prestressed a concrete beam AB of span l it is subjected to an external load of w/m length prestressing force p, prestress is imparted to beam with help of parabolic tendon with dip of h at centre due to parabolic profile beam is subjected to upward uniform force We is given as p_x = p = w_el²/8h.

Z = 18×10⁵mm³, A = 36×10³mm², G = (0.1×0.4×24) = 0.96kn/m
Total load W = (g+q) = (0.96+3.14) = 4.1kn/m, Maximum working moment = (0.125×4×6²) = 18.45knm
(M/Z) = (18.45×10⁶/18×10⁵) = 10.25n/mm².

The cable profile in a prestressed member corresponds to shape of bending moment diagram resulting from external loads, in a prestressed concrete member external type of loads are balanced by transverse component of suitable cable profile.

It is generally considered that visible cracks appear when tensile stresses at soffit are approximately equal to modulus of rupture of material, it is an ultimate strength pertaining to failure of beams by flexure equal to bending moment at rupture divided by section modulus of beams.

Up to stage of visible cracking on concrete, changes in stress of steel, loading being negligibly small, are generally not considered in computations, phenomenon of stress corrosion in steel is particularly dangerous, as it results in sudden brittle fractures.