Wire Breakage Detection Using Relative Strain Variation in Unbonded Posttensioning Anchors

Recent problems with grouted posttensioning tendons in U.S. bridges have led to interest in tendons that are not grouted, but rather filled with a pliable corrosion protection system such as grease or wax. The use of a flexible filler material in place of cementitious grout results in an unbonded tendon, which not only affects the structural behavior but also enables the application of new methods for improved monitoring and maintenance. This paper outlines a novel continuous monitoring approach that aims to detect wire breakage in unbonded tendons based on relative strain variation in the anchor head (or wedge plate). The feasibility of the method is investigated using a finite-element model calibrated with experimental data from a seven-strand anchor head. The model is subsequently extended to a 19-strand anchor head to assess the method’s performance on detection, localization, and quantification of tendon damage. The numerical results confirm the correlation between wire breakage and relative strain variation among the monitoring points and illustrate the method’s effectiveness in determining the location and severity of damage.

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