As these tendons are individually greased and plastic coated, they are permanently de-bonded from the slab. If unbonded tendons are severed, the prestressing force will be lost along the entire length of the tendon. Consequently, when contemplating the cutting of an unbonded tendon, it is imperative to consider the aspects noted below.
Cutting the tendons
When the tendon is severed, the grease between the strand and the end prevents a sudden explosion of energy. However, a gradual release of force is recommended. In this case, two open-throat jacks are used back-to-back. By closing the jacks on the end of the strand, the force can be released gently.
Propping the slab
Adjacent spans may require temporary propping depending upon the number of tendons severed at one time. It is rare for a slab to carry its full design load. A design check based on actual loading at the time of the modification may show props to be unnecessary.
Forming the hole
When the edge of the slab is re-concreted new anchors are cast in to enable the remaining lengths of the tendon to be Prestressed, thus restoring full structural integrity. The above operations are not difficult but will require the expertise of a post-tensioning sub-contractor.
