Disadvantages Of External Prestressing
The various disadvantages of external pre-stressing are described as below:
(i) Only straight profile of tendon is possible.
(ii) Additional cost for ducts and anchorages.
(iii) Diffusion of Post-Tensioning forces.
(iv) External tendons are more sensitive to fire and more easily attackable by the vandals.
(v) The pre-stressing force disappears over the overall length of the tendon once a section of tendon is broken.
(vi) External tendons are protected by HDPE ducts which are fully cement grouted or wax filled which result in a higher initial material cost for the pre-stress system.
(vii) Under ultimate bending conditions external tendons require more pre-stressing to generate the same moment of resistance.
(viii) Anchorage points and deviators are subjected to high concentrations of forces which need to be properly tied into the structure.
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