A tendon monitoring framework for unbonded post-tensioned bridges based on anchor strain response

Post-tensioned segmental bridges are common throughout the U.S.; however, in recent years, the incidence of tendon failure in bonded post-tensioned bridges has raised questions regarding their design, construction, and maintenance. These failures have led to interest in tendons that are not grouted, but rather filled with a pliable corrosion protection substance such as grease or wax. The use of a flexible filler material in place of cementitious grout results in a replaceable unbonded tendon, which results in changes in global strand and anchor response in the event of a wire break, enabling the application of new methods for improved monitoring and maintenance. This research focuses on developing a robust monitoring system for unbonded tendons with the ultimate intent of detecting strand damage to provide maintenance decision support. The scope of research includes examining the applicability of existing approaches for tendon monitoring, such as acoustic emission technique and electro-mechanical impedance method, developing new approaches that are particularly suitable for unbonded tendons, and performing detailed analytical studies on the behavior of tendons and anchors subjected to varying levels of damage.;In unbonded systems, large prestressing force results in large strain gradients over the anchors and the strain distribution undergoes significant changes due to a wire break. Based on the relative strain change among discrete monitoring points in anchors, a novel approach has been developed that overcomes many of the challenges faced by the existing approaches. The feasibility of this method was confirmed by detailed analytical models, followed by experimental measurements. An efficient monitoring algorithm was developed to detect a breakage event and identify the broken strand programmatically. A sensitivity study of measurement errors was conducted to examine the robustness of the proposed model.;The practicality of the monitoring system was assessed through analytical characterization of the stressing and breakage response of a prestressing strand. Both static and dynamic post-breakage behaviors of the strand were analyzed with various confinement conditions. The analysis captured many localized and global strand responses that facilitate a comprehensive understanding of its mechanical behavior. In addition, multiple full-scale experiments with both internal and external tendons were conducted to investigate the performance of the proposed monitoring system. These investigations provide useful insights on stress recovery and load distribution among wires, which have important implications on breakage detectability.;The full-scale testing confirmed that wire breaks result in significant strain change in the anchors both in external and internal waxed tendons with deviated profiles. Furthermore, full stress recovery did not occur under any tested conditions. The analytical models successfully captured the anchor strain response and complex mechanical behavior related to wire breaks, including post-break dynamic response. In addition, the developed breakage detection algorithms have been proven successful in identifying the broken strand.