Types of Losses of Prestress in Prestressed Concrete

Losses in case of Pre Tensioned Prestressed Concrete

1. Loss due to Elastic Shortening: Suddenly, after applying the prestress to the concrete, it undergoes elastic deformation which is also simultaneous and equal to the change in the length of the prestressing tendon. This leads to loss of the prestress.
2. Loss of prestress 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: Relaxation is the loss of stress under the condition of constant strain.

Losses in Post Tensioned Prestressed Concrete

1. Loss Due To Anchorage Slip: This type of loss occurs only in Post Tensioned elements. While applying or particularly transferring stress, the slip of steel tendons or strands slip. This leads to loss of stress in the prestressing steel.
2. Loss of Prestress 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 of Prestress due to creep of Concrete: Creep is the time-dependent part of strain. It is the strain because of continuous stress.
4. Loss due to shrinkage of concrete.
5. Loss Due to Relaxation of Steel: Relaxation is the loss of stress because of continuous strain. In prestressed concrete steel cables lose their stress over time because of relaxation.
6. Loss of stress due to friction between concrete and prestressing steel.

Also Read-
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External Links
You can refer site of Prestressed Concrete Institute PCI.org for more details