Elastic shortening is the loss in prestress due to the elastic deformation of the structure under the applied load. It is not a time-dependent loss because it occurs immediately upon the application of the load and does not change with time.

Explanation:
- Elastic shortening occurs when an initially straight and stress-free prestressed member is subjected to an external load. The member will deform elastically, causing a reduction in the prestress force.
- This loss is immediate and does not change with time. It is primarily dependent on the elastic properties of the material and the magnitude of the applied load.
- Elastic shortening is a reversible deformation, meaning that when the load is removed, the member will return to its original shape and prestress force will be regained.
- It is important to consider elastic shortening while designing prestressed structures to ensure that the anticipated loss in prestress is accounted for in the initial design and the prestress force is sufficient to resist the applied loads.

Comparison with other losses:
- Creep, which is a time-dependent loss, occurs due to the gradual increase in deformation of a material under a sustained load. It happens over a long period and leads to an additional loss of prestress over time.
- Shrinkage is also a time-dependent loss that occurs due to the reduction in volume of the concrete as it dries and ages. It leads to a contraction of the prestressed member and a loss in prestress force.
- Relaxation is another time-dependent loss that occurs due to the relaxation of the prestressing steel over time. It is caused by the redistribution of stress within the steel and results in a reduction in the prestress force.

In summary, elastic shortening is an immediate loss in prestress that occurs upon the application of the load and does not change with time. It is important to consider this loss in the design of prestressed structures to ensure the desired level of prestress is achieved and maintained.