The deformation or change in mass under sustain loading is called creep.
Main aspects of Creep / Deformation in Concrete
The deformation of concrete depends on various aspects as follows:-
- Concrete strength
- Strength of concrete at the time of transfer of theload
- Applied stress level
- Humidity and atmospheric condition
- Time at which its deformation is measured
Loss of Pre-Stress due to Creep of Concrete
The loss of pre-stress under load shall be determined for all the permanently applied loads including the pre-stress. Its loss due to live load stress, erection may b ignored. The loss of pre-stress due to creep of concrete is obtained as a product of modulus of elasticity of the pre-stressing steel and ultimate creep strain of the concrete fiber integrated along the line of center of gravity of pre-stressing over its entire length.
The total creep stain during any specific period shall be assumed for all practical purpose, to be creep stain due to sustained stress equal to the average of stresses at the beginning and end of the period.
National building codes adopt different formula for calculating the creep stain which involves not only the age of concrete at which the stress is transferred but also the cube strength, relative humidity etc.