Chapter: Bridge Works Civel engineering engineer doubt problem guide and intrview questions and answer
Under what situation shall engineers use jacking at one end only and from both ends in prestressing work?
Under what situation shall engineers use jacking at one end only and from both
ends in prestressing work?
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 fact, stressing at one end
only has the potential advantage of lower cost when compared with stressing
from both ends. For multiple spans (e.g. two spans) with unequal span length,
jacking is usually 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.
Related Topics