Difference Between Short And Long Term Deflections (Limit State Of Serviceability)

Difference between Short- and Long-term Deflections:

Short-term deflection means the immediate deflection after casting and application of partial or full service loads, while the long-term deflection occurs over a long period of time largely due to shrinkage and creep of the materials.

The following factors influence the short-term deflection of structures:

(a) Magnitude and distribution of live loads,

(b) Span and type of end supports,

(c) Cross-sectional area of the members,

(d) Amount of steel reinforcement and the stress developed in the reinforcement,

(e) Characteristic strengths of concrete and steel, and

(f) Amount and extent of cracking.

The long-term deflection is almost two to three times of the short-term deflection.

The following are the major factors influencing the long-term deflection of the structures:

(a) Humidity and temperature ranges during curing,

(b) Age of concrete at the time of loading, and

(c) Type and size of aggregates, water-cement ratio, amount of compression reinforcement, size of members etc., which influence the creep and shrinkage of concrete.