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A basic explanation of how post-tensioning works from The Post-Tensioning Institute.

These illustrations describe the typical procedure in which tendons were originally placed, stressed, and greased in Nuclear Containment Buildings.

1. Prior to pouring concrete, semi-rigid steel conduit of the appropriate diameter was set in its pre-determined position. This conduit was attached at each end to the steel trumpet bearing plate assembly (called the "trumplate"). These trumplates were bolted to the concrete forms prior to connecting them to the conduit.

2. The tendons were coiled at the manufacturing plant and shipped to the site on specially designed racks. The coiled tendons were transferred to the uncoiling reel which was positioned at the shop anchor stressing location. The tendons were then winched through the metal conduit with the help of a powered tugger at the opposite end.

3. The wires were installed in the field anchor and button-headed. ( The wires in the shop anchor at the opposite end were buttonheaded at the factory.) A winch at the shop anchor end pulled the tendon back through the conduit to a taut position.

4. A threaded bushing was screwed onto the shop anchor head. The pull rod of the stressing jack was then attached to this bushing.

5. The tendon is ready for stressing. Depending on design considerations, tendons were stressed either at both ends or at one end only. The anchors at both ends accepted the identical stressing jack.

6. A hydraulic jack was coupled to the anchor to be stressed and exerted equal pull on the wires which were held securely in the anchor by their buttonheads. As the tendon elongated and the anchor was pulled away from the bearing plate, steel shims, of varying thicknesses, were inserted. When the required tendon elongation had been attained, the anchor was brought to rest on the shim stack.

7. The tendon was now fully stressed and ready for greasing.

8. Gasketed grease caps were positioned over the anchors at each end, and grease was pumped into the grease cap and through the conduit under pressure, completely encasing the tendon and its anchors for permanent corrosion protection.