Bond between steel strand and cement grout in ground anchorages

Bond action between prestressing strand and cement grout is examined both theoretically and experimentally. Variations in strand type, embedment length, grout strength and lateral compression are investigated using a modified pull-out specimen and a simple test rig. The results support the recommended value of ultimate bond stress of 2 N/mm²proposed in the British Standard Draft for Development DD81: 1982 but show that this value may be trebled by the introduction of biaxial lateral pressure. A theoretical expression is derived, based on a frictional force mechanism, which predicts the bond strength of normal and Dyform strand. The bond characteristics of indented strand are found to be similar to those of deformed bars. A wedge action, which is attributed to “lack ofjit” of strand within the grout channel, is shown to play an important role in the establishment of a stable load/slip bond characteristic.