When should an engineer use jacking at one end only and from both ends in prestressing work? [Practical Civil Engineering Question]

When should an engineer use jacking at one end only and from both

ends in prestressing work?

During the pre-stressing process, if prestressing is carried out at one end only, frictional losses will occur and the prestressing force will be minimized along the tendon length till the other end. This frictional loss includes the friction caused due to change in curvature of tendons & loss due to deviation of tendon alignment from centre line i.e. wobbles effect. Because of this the prestressing force in mid span and far end span is highly minimized due to high frictional loss.

In order to avoid such a situation, to provide even distribution of prestress & symmetry of force along the length prestressing is carried out at both the ends.

In fact, pre stressing at one end only has the potential advantage of lower cost compared to stressing from both ends. For multiple spans having unequal span length,

Jacking will be carried out at the end of the longer span so as to provide a higher prestress force at the location of maximum positive moment. On the contrary, jacking from the end of the shorter span would be conducted if the negative moment at the intermediate support controls the prestress force. However, if the total span length is sufficiently long,   jacking from both ends should be considered.