Full-scale experimental investigation of wire breakage detection in deviated multi-strand tendon systems

Abstract

The use of post-tensioning tendons with flexible filler is expected to increase in U.S. bridges in the coming years as an alternative to grouted tendons. Flexible filler results in purely unbonded behavior when used with either internal or external tendons, which creates opportunities for the application of tendon monitoring techniques that were not possible with grouted tendons. One such technique is the detection of wire breakage based on the strain response of the post-tensioning anchorage. The encouraging results from simplified laboratory experiments and analytical models in support of the proposed method motivated the full-scale experiments reported in this paper. Tests were conducted with flexible filler in both external and internal tendons in I-girder specimens having deviated multi-strand tendon profiles, allowing the investigation of the effects of deviators on stress recovery and anchor strain response. The strands of the post-tensioned girders were detensioned by individual wire cuts and the resulting changes in anchor strain distribution were captured. Finally, a broken strand identification algorithm developed for automated damage detection was applied to the experimental results. In addition to instrumenting the anchors with strain gauges, an acoustic sensing system was employed to independently monitor and confirm the breakage events. The findings reported in this study suggest that the wire breakage detection method based on anchor strain measurement can be a reliable and cost-effective approach for in-field bridge monitoring applications.