i think, During prestressing operation at one end, frictional losses will occur and the prestressing

force decreases along the length of tendon until reaching the other end. These frictional

losses include the friction induced due to a change of curvature of tendon duct and also the

wobble effect due to deviation of duct alignment from the centerline. Therefore, the

prestress force in the mid-span or at the other end will be greatly reduced in case the

frictional loss is high. Consequently, prestressing, from both ends for a single span i.e.

prestressing one-half of total tendons at one end and the remaining half at the other end is

carried out to enable a even distribution and to provide symmetry of prestress force along

the structure.

In pretensioning system Dr.Abbas

Good Dr Amjad