Multistrand Post-Tensioning Anchor Evaluation Tests

The multistrand post-tensioning (PT) anchorage tests will focus on key variables related to self-centering wall systems: post-yield cyclic loading, anchorage capacity after a seismic event, rotation between multistrand anchorages, and durability details. Tests will be conducted prior to the shake table and wall-floor sub assemblage studies to finalize the test details. The PT anchorage system will also be investigated post-test, if needed, to analyze any unexpected phenomena observed in the large-scale tests. Two manufacturers of 7-wire multistrand anchorages will be tested under monotonic and cyclic loading procedures. Multistrand anchorages have unique challenges in quantifying their response in a self-centering wall system. Even in a straight tendon, strands will tend to twist along the length between the dead and live end anchorages. This rotation can have an effect on the behavior of the tendon under large deformations and has the potential to reduce the failure load of the tendon. Additionally, previous research has indicated that stress concentrations at the nose of the wedge within anchorages can reduce the failure load of the tendon and greatly reduce ultimate strains. This behavior will be verified and addressed through extensive testing of a modified wedge geometry that balances the normal force on the strand more evenly over the length of the wedge, thus reducing the stress concentration at the nose. Durability is a key component to any post-tensioned system. The most widely used internal unbonded PT tendon system in practice is a greased/sheathed monostrand system (PT coating with extruded plastic sheath). Unbonded internal multistrand systems are much less common. For the systems described in this project, details will be developed for a greased system applicable to multistrand PT tendons in walls.