The British code (BS: 8110-1985) specifies a maximum deflection limit of span/250 beyond which sag in a member will be usually become noticeable and to prevent damage to non-structural elements, code recommends that deflection after installation of finishes & partitions should not exceed span/500 or 20mm whichever is less for brittle members.

The deflections of prestressed concrete members are influenced by following salient features: imposed load and self weight, magnitude of prestressing force, cable profile, and second moment of area of cross section, modulus of elasticity of concrete, shrinkage, creep, relaxation, span, and fixity conditions.

The philosophy of design termed as ?Limit state approach? adopted by Russian code in 1954 and American and British codes in 1971, it requires a proper knowledge of behavior of structural concrete members at multiple limit states, of which deflection forms an important criterion for safety of structure.

It is general practice in most of codes to safeguard against excessive deflections under serviceability limit states, eir indirectly by prescribing a minimum span to depth ratio for member or directly by specifying a maximum permissible deflection expressed as a fraction of span and recommendations of Indian standard code with regard to limit state of deflections is IS: 1343-1980.

When beam AB is subjected to a bending moment distribution due to prestressing force or self weight or imposed loads, ACB is centre line of deformed structure under system of given loads, According to Mohr?s first orem
Slope = area of bending moment deflection/flexural rigidity, ? = A/EI.

The creep strain due to transverse loads is directly computed as a function of creep coefficient so that change of curvature can be estimated by expression,
?_mt = (1+?)?_i,
? = creep coefficient, ?_i = initial curvature immediately after application of transverse loads.

The deflection in sloping tendon is computed in a way similar to:
A = (-PL²/12EI (e₁+e₂)) + (Pe2L²/8EI)
A = (PL³/24EI (-2e₁+e₂)).

Floors not supporting and not attached to non structural element likely to be damaged by large deflections and are carried by immediate deflection due to live load and deflection limitations are given as (span/360).

In pre cracking stage whole cross section is effective and deflections in this stage are computed by using second moment of area of gross concrete section, as length of structural member increases deflections can be controlled to a maximum extent possible.

The British code BS: 8110-1935 recommendations are comprehensive in this regard, as y incorporate use of curvature of cracked sections, including effect of shrinkage and creep in computing long term deflections.