Question

The loss due to creep in pre-stressed concrete shall be determined considering
1. All loads and pre-stressing force
2. Live loads and pre-stressing force
3. Permanent loads and pre-stressing force
4. Permanent loads only

Answer 1

Correct Answer - Option 3 : Permanent loads and pre-stressing force

Concept:

As per IS 1343(1980): Code of Practice for Prestressed Concrete 19.5.2.1

Loss of prestress due to creep of concrete:

• The loss of prestress due to the creep of concrete under load shall be determined for all the permanently applied loads including the prestress.
• The creep loss due to live load stresses, erection stresses, and other stresses of short duration may be ignored.
• The loss of prestress due to creep of concrete is obtained as the product of the modulus of elasticity of the prestressing steel and the ultimate creep strain of the concrete fiber integrated along the line of center of gravity of the prestressing tendon at the section at which creep loss is being calculated for bonded tendons.
• In the case of unbonded tendons, the creep loss is a product of modulus of elasticity of prestressing steel and creep strain calculated by integrating and averaging creep stress along the line of center of gravity between the anchorage points.
• The total creep strain during any specific period shall be assumed for all practical purposes, to be the creep strain due to sustained stress equal to the average of the stresses at the beginning and end of the period.