Types of Application of External Prestressing
In total, then a three types of applications of external pre-stressing applicable to bridges which are mentioned as below:-
(i) In the first type, the unbounded pre-stressing tendons/cables comprise the total pre-stressing force. Segmentally constructed bridge and cast-in-situ box girder bridge superstructure using external cables are an example of this category.
(ii) In the second type, the unbounded elements act as part of total pre-stressing force, the other part being provided by bounded pre-stressing elements embedded in concrete. External pre-stressing provided for repair/rehabilitation/strengthening of existing PSC bridge is an example of this type. The external pre-stress may or may not contribute to the enhancement of ultimate strength.
(iii) In the third type, the external pre-stressing is used as a means of applying external load acting in the desired direction and quantum and the deformation of the structure due to subsequent live load-both in service and under ultimate condition do not affect the magnitude and direction significantly. The external pre-stressing is taken as equivalent load only without considering its contribution to the strength of the structure. This type of application is used in strengthening of existing RCC structure by using pre-stressing elements to relieve part of the dead load effects.
tendon placement in external post-tensioning
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