The cold worked high tensile alloy steel bars to BS: 4486 has a modulus of elasticity of 175kn/mm² and initial prestress should not normally exceed 70% of characteristic tensile strength and in no case should it exceed 75% at time of initial tensioning, at time of final stress after allowing losses of prestress not greater than 60% of characteristic tensile strength of tendons.

P_x = 600n/mm², e = 2.7183, ? = 0.5
P_x = P?e^-??,
600 = P?e-^(0.5×?/2),
P? = (600) × (2.7183^0.79) = 1320n/mm², Average stress in wires = (1320+600/2) = 960n/mm².

The initial prestress in concrete undergoes a gradual reduction with time from stage of transfer due to various causes and this is generally referred to as ?loss of prestress? since re is no bending moment at span stress in tendon changes only at midspan but not at end since concrete and steel are considered as one section after bonding change in stresses due to bending of this section can be calculated by using transformed section method.

The use of high strength concrete with low water cement ratios results in a reduction in shrinkage and consequent loss of prestress, aggregates of rock type having high modular of elasticity and low values of deferred strain are more effective in restraining contraction of cement paste and ir use reduces shrinkage of concrete.

In high tension strength steel, it is noticed that at a particular time stress in steel reduced at a constant value of strain and this phenomena of reduction of stress in steel at a constant strain is known as relaxation of stress.

Loss of stress in steel due to elastic shortening is ?_ef_c,
?_e = E_s/E_c = modular ratio, f_c = prestress in concrete at level of steel, E_s = modulus of elasticity of steel, E_c = modulus of elasticity of concrete.

The Indian standard code IS:1343 is recommended for loss of prestress due to shrinkage of concrete, individual shrinkage strains are evaluated from British code BS 8110 shrinkage stresses are calculated.

The total residual shrinkage strain will be larger in pretensioned members after transfer of prestress in comparison with post tensioned members, where a position of shrinkage will have already taken place by time of transfer of stress.

The method used for slip in anchorage by extending tendon is satisfactory provided by overstress does not exceed prescribed limits of 80-85percent of ultimate tensile strength of wire and magnitude of loss of stress due to slip in anchorage is computed as
Anchorage slip ? = PL/AE_s, But moment Loss of stress, (?f)_a = P/A,
By considering both equations (?f)_a = E_s?/l.

The loss of stress due to curvature effect, which depends upon tendon form or alignment which generally follows a curved profile along length of beam, curvature coefficient is expressed as ? and wobble coefficient is expressed as k/m.