Types of losses of prestress in prestressed concrete

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In pretensioned and post-tensioned prestressed concrete, losses are different.

Losses in case of pretensioned prestressed concrete

  1. Loss due to elastic shortening

    Suddenly after applying of the prestress to concrete, it undergoes elastic deformation which is also simultaneous and equal change in length of prestressing tendon. This leads to loss of prestress.

  2. Loss due to creep of concrete

    Creep is a time dependent part of strain. Also when the load is removed from the element or even from the entire structure, a part of strain or particularly say deflection is even there. This permanent defect is called creep.

    As time elapses, the creep will be induced in the structural element because of permanent loading. This lead to loss of prestress in concrete.

  3. Loss due to shrinkage of concrete

    Shrinkage is property of concrete which could be defined as a reduction in the volume with time. This leads to loss of prestress in steel.

  4. Loss due to relaxation of steel

In post tensioned prestressed concrete following losses are to be faced

  1. Loss due to anchorage slip
  2. Loss due to elastic shortening of concrete. This loss occurs only if prestressing cables are tensioned successively. If we impart prestressing force simultaneously to all of the cables then this loss can be avoided.
  3. Loss due to creep
  4. Loss due to shrinkage
  5. Loss due to relaxation of steel

    Relaxation is loss of stress because of continuous strain. In prestressed concrete steel cables loses their stress over time because of relaxation.

  6. Loss due to friction between concrete and prestressing steel

Further reading

Prestressed concrete advantages and disadvantages

IS 1343-2012 pdf download

You can refer site of Prestressed Concrete Institute PCI.org for more details

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