Multi-Stage Strand Anchors
DYWIDAG Stand Anchors
The multi-stage strand anchor has been developed from the need to achieve greater anchor loads in poor ground conditions. It offers uniform distribution of load over the full bond length in addition to efficient utilisation of the in-situ ground strength.
Conventional ground anchors are limited to a maximum fixed length of 10m (BS 8081); extending the conventional fixed length will not produce a gain in load carrying capacity, because any higher loading would induce progressive de-bonding from the proximal end of the fixed anchor length due to stress concentration.
The multi-stage anchor accommodates any uneven distribution of load by employing individually staged bond lengths along the fixed length. It provides the solution where ground conditions dictate a fixed anchor length greater than that achievable with a conventional anchor. Multi-staging enables the fixed length to be increased in proportion to the number/length of stages. Through efficient distribution of load over the entire fixed anchor length, the multi-stage anchor is able to develop proportionately higher loads than conventional anchors.
The technique of staging individual bond lengths within the fixed anchor length, ensures an even distribution of load.
Individual bond lengths, in conjunction with the borehole diameter, are matched to the soil strength. Typical bond lengths range from 2 to 4.5m; in general, bond lengths within this range offer the most efficient distribution of load, but longer bond lengths are available to suit particular ground conditions.
Bond stress performance is enhanced along the tendon/grout interface by noding of the strands.
Fixed length extension is matched to the extension characteristics of the soil.