VIDEO: Field Friction Test for Post Tension Tendons

This educational video from AMSYSCO, Inc. shows the process for determining the Friction Coefficients.

Post Tensioning Institute (definitions):

  • Friction Loss:  the loss of stress (force) in a prestressing tendon resulting from friction created between the strand and sheathing during stressing.
  • Wobble:  the friction caused by the unintended horizontal deviation of the tendon.
  • Angular Curvature:  the friction caused by the profile of the tendon.

American Concrete Institute (ACI-318 Chapter 18, Table R18.6.2) gives ranges for Bonded and Unbonded post tensioning tendons.  The lower the Wobble and Angular Curvature friction coefficients are, the higher the force per tendon. A higher force per tendon can help solve field issues such as broken tendons or under-elongations.

AMSYSCO, Inc. recently conducted a field friction test in 2009 for our 0.5? diameter Unbonded Post Tension Tendon.  We used the “load-cell” method (shown in the video) and our friction coefficients outperformed the recommended values given by American Concrete Institute.  To request a copy of our results, please email us at

Copyright © 2009 by AMSYSCO, Inc. All rights reserved.

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