Health Monitoring to Detect Failure of Prestressing (PS) Cables in Segmental Box-Girder Bridges

摘要

This project aimed at developing and demonstrating a health monitoring system for prestressing (PS) tendons in post-tensioned concrete structures, including the popular segmental box-girder bridges. The technique under investigation was based on ultrasonic guided waves and embedded sensors. The goal was to provide both detectability of defects in the tendons such as corrosion and broken wires, and measurability of applied prestress levels. The report first presents the literature review of the techniques available for health monitoring of concrete structures, particularly cables and PS tendons. The subsequent sections present the results obtained from both numerical simulations and experiments of wave propagation in unloaded and loaded seven-wire strands, both free and embedded. Of particular interest is the identification of certain linear and nonlinear ultrasonic wave properties which were sensitive to the level of prestress applied to the strands. Those features were exploited, in combination with acoustic emission technique, to monitor the stress level in strands and to detect and localize defects during the testing of large scale post-tensioned concrete joints at UCSDs Powell Laboratories. The work in this project indicates that ultrasonic probing of the PS strands can indeed be effective for the detection of defects as well as for the monitoring of PS forces in post-tensioned concrete structures. Based on the findings of this research, strategies for both realtime health monitoring and routine-based inspection of post-tensioned bridges are outlined. These strategies will need to be validated in a follow-on project focusing on additional large-scale laboratory tests and field testing of bridges in service.