Working stress measurement of prestressed anchor cables: Detection mechanism and experimental study of lift-off test

The prestressed anchor cables are critical structural elements in ground anchors. Because of the widespread use of ground anchors in geotechnical engineering, the measurement of working stress of prestressed anchor cables in ground anchors becomes imperative. The lift-off test is currently practiced in China and many other countries for this purpose. However, the interpretation methods of testing results are different and country dependent. The interpretation method employed in China is examined by experiment and theoretical analysis that are presented in this paper. The experimental verifications are performed to apply a couple of lift-off tests on a anchor cable prestressed to its 75% ultimate strength. The results show that averaged load in the bending regime on the load-displacement curve recorded during lift-off tests can approximate the working stress of this anchor cable monitored with load cells installed. According to theoretical analysis the measuring principle of list-off tests is better understood.