Stressing / Lock off of GT Systems

Test and tension service for installed ground anchors.

Whether for maintenance, service, or inspection reasons, there are times where ground anchors need to be tested to determine the existing force after installation and lock-off. If this measure was already taken into account during the manufacture of the anchor and there is an external thread or other projection, this is easy to do. Occasionally, however, for strand anchors in particular, the existing anchor force must be determined later, although this was not originally intended. With our patented Lift-Off Device, we can now carry out a lift-off test on strand anchors with smooth wedge plate to determine the anchor force. ​

This service is useful for temporary anchors which have been installed for over two years, and can identify a range of issues, such as the influence of external corrosion, if the wrong system was chosen, any damage caused during transport and storage, if there were errors during installation, if corrosion protection is insufficient, incorrect head design, any mechanical damage to the head, or other damage. ​

The wedge plate is gripped with a clamping bell and a stressing jack with tensioning spindle is mounted on top. The applied force is determined either with a load cell, or calculated using the hydraulic pressure on the hydraulic pump and the piston area of the calibrated stressing jack. The load steps are determined depending on the expected anchor load. The anchor-head displacement is measured with a precision dial gauge. During stressing, initially only the tensioning spindle between the anchor head and the nut on top of the stressing jack is stretched. When the existing anchor force is exceeded, the wedge plate lifts off the anchor plate. As the force increases further, the entire tendon of the anchor in the free length up to the grout body is stretched. ​

For evaluation, a force-displacement diagram can be created. This results in two differently inclined lines whose intersection corresponds to the current anchor force. ​

  • Extension of service life for temporary anchors installed for over 2 years​

  • Easily fulfil maintenance or servicing measures, or regular inspection regimes​

  • A wide range of issues can be detected from the test so that the right solution can be implemented the first time

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