The deflection of cracked structural concrete members may be estimated by Unilinear or bilinear method recommended by European concrete committee, slope of first line corresponding to stiffness of uncracked section and slope of second line to that of cracked section.

The deflection of prestressed members can be computed relative to a given datum if magnitude and longitudinal distribution of curvatures for beam span are known based on load history including prestressing forces and live loads.

Cracks of limited width are acceptable under occasional overloads or even under working loads according to CED-FIP recommendations and knowledge of load deformation characteristics of cracked members is essential to comply with limit state of deflection.

The revised American code considers bilinear character of load deflection characteristics by incorporating a suitable effective value of flexural rigidity in unilinear formula, In Unilinear method, deflections are computed by a simple equation of form
A = ?L²M/E_cI_t, a = maximum deflection, L = effective span, M = maximum moment in beam, E_c = modulus of elasticity of concrete, I_c = second moment of area equivalent cracked moment, ? = constant.

The computations of deflections in this stage are made by considering moment curvature relationships which involve section, properties of cracked beam, based on prestressing forces and live loads deflections of prestressed concrete members can be calculated if longitudinal distribution of curvatures and magnitude of beam can be known at that particular time.

The FIP-1984 recommends following suitable deflection limits for floors, roofs and or horizontal members in building limits for deflection that occurs after addition of partitions up to:
Span/500 to Span/1000.

A draped tendon with a trapezoidal profile considering bending moment diagram deflection at centre of beam is obtained by taking moment of area of bending moment diagram over one half of span A = ?Pe/6EI(2l₁²+6l₁l²+3l₂²).

According to Neville and ACI committee report, creep curvature is obtained due to prestress based on a very simplified assumption that creep is induced into concrete by average prestress acting over with respect to given time.

In both pre and post cracking stages effect of creep and shrinkage of concrete is to increase long term deflections under sustained loads, which is estimated by using empirical methods that involve use of effective (long term), modulus of elasticity or by multiplying short term deflections by suitable factors.

The deflection including effect of temperature, creep and shrinkage occurring after erection of partitions and application of finishes should not normally exceed span/350 whichever is less, creep is directly proportional to stresses but above this value it increases more rapidly.