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Ground anchors
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Installation

The accuracy of the prestressing force actually introduced into the structure and the durability of the tendons depend on the quality of the installation works.
Shimming of the anchorages
When anchorages are applied onto an existing concrete element, it is recommended to shim under the bearing plate using a non-shrink mortar, free from chloride.

Two types of jacks
can be used: with a tie rod connected to the tendon or with a direct connection. Jacks should be used in conjunction with Freyssinet hydraulic pumps, with high pressure and a low flow rate to allow a progressive tensioning of the bar.


Tensioning

The tensioning equipment provided by Freyssinet ensures the accuracy of the load applied within +/- 2%. This is achieved through regular calibration of the pump pressure gauge and the jacks.

Safety factors

The tensioning force in the prestressing bars is given by the relevant design standards. Recommendations are given below as examples: (Note: Fpk means the guaranteed tendon tensile breaking load).
A) In post-tensioned structures, the French rules (BPEL91 revision 99) limit the stressing force to 0.70 Fpk.
B) In prestressed ground anchors, the norm EN 1537 prescribes a final force limited to 0.60 Fpk. The tensile force for the preliminary inspection and reception tests being less than 0.80 Fpk.
C) In case of re-use, the tensioning force of the bar is limited to 0.60 Fpk for the first use, and to 0.50 Fpk for all subsequent uses.

Tensioning jacks

Notes : A/ Diameter adaptations must be indicated when ordering the jacks, in the following manner: CF 110 for 26.5 and 40 mm : CF 110-ADP-26.5/40 B/ Bars fitted with hinge anchorages shall be tensioned exclusively by means of a jack with a hinge.


Tensioning pumps

The injection compounds

The bars and the anchor heads should be protected against corrosion either by using a cement mortar or a wax. Freyssinet recommends the ready mix SUPERSTRESSCEM for the standard applications and the thixothropic and retarded cement mix SMARTGEL, which avoids any segregation or settlement of the grout, in case of vertical or highly inclined tendons.
To allow for subsequent re-tensioning of the bars, the injection must be achieved with a flexible anti-corrosion product. Freyssinet recommends the Freyssinet/Elf CP-HPF wax, specially designed for prestressing and stay cables.

The injection equipment

Freyssinet has designed specific injection equipment which ensures the proper filling of the ducts.