Anchorages for unbonded Post-tensioned Flat Slabs

Testing of Anchorages

Post-tensioning systems are either bonded or unbonded. The bonded system is used in heavy civil works, such as bridges, reservoirs, silos etc. and allows a number of strands to be used in one duct or sleeve. The sleeve is then later led with cementitious grout for bonding purposes and corrosion protection.

The unbonded system is generally used in the slab and beam elements of reinforced concrete building structures. This system makes use of single strands contained in plastic sheaths, which are cast into the concrete and then tensioned once the concrete has reached succinct strength.

Both systems allow structures to have greater spans as well as reduce propping time whilst the concrete is attaining its full strength. These advantages result in significant cost and time savings. The post-tensioning principle is also applicable to stay cables, external cables and ground anchors using strand or bar systems.

D&E POST TEN can be contracted to carry out one or a combination of the following:

  • Supply of materials, equipment and training
  • Full supply and installation
  • Design can either be done in-house or in conjunction with the
  • professional engineer of record

Testing of Anchorages

Post Ten unbonded anchorages have been tested in accordance with B.S 4447; October 1973. “The specification for the performance of Pre-stressign Anchorages for the post-tensioned construction”. These tests include the Static Test, where the complete anchor system is tested in a concrete block at various concrete strengths, and Dynamic Test, where a fluctuation force between 0.60fpu and 0.60fpu is applied for a minium of 2×106 cycles.

Strand

Post Ten only use 7 wire plastic sheathed strand to B.S. 5896 super grade material of either the following sizes: 12,9mm diameter U.T.S. 186Kn 15,7mm diameter U.T.S. 265Kn. We recommend that the initial stressing force does not exceed 80% of U.T.S

The Anchorage System

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