United States Department of Transportation
i
Optical Fiber Sensor-Embedded Strands for Long-Term Monitoring of Post-Tensioned Tendons in Bridge Elements
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2024-06-01
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[PDF-6.42 MB]
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Abstract:Tendon forces are fundamental to the performance of post-tensioned (PT) bridges. Therefore, monitoring tendon forces is important for understanding the health of PT bridge elements and evaluating the condition of prestressing strands. Implementing a reliable method to monitor PT tendons during the service life of the structure, however, is a challenge. The ideal technology should provide a measurement of prestress (or strain) over the length of the tendon and not be limited to measurement only at discrete locations. When installed along the length of PT tendons, optical fiber sensors provide a promising means to overcome many of the challenges of tendon force monitoring that currently exist. The technology offers the ability to assess the strain along the length of PT tendons as the bridge is in service. A research project was conducted to evaluate the use of optical fiber sensors in new PT bridges as a means for long-term monitoring of tendon force and identification of unexpected changes (i.e., losses) in prestress. More specifically, the use of optical fiber sensors embedded within epoxy coating along the length of prestressing strands was assessed. The test program included in the research was aimed at evaluating the accuracy and reliability of data acquired from the optical fiber sensors. The program consisted of tests on optical fiber sensor-embedded prestressing strand specimens in a universal testing machine and installed in a prestressing bed in the laboratory. Then, the strands were used to post-tension beam specimens, allowing the strain data to be evaluated during the post-tensioning procedures and during load tests on the beams. The experimental results from the beam tests were compared to the results from analytical models of the specimens to further assess the strain data from the optical fiber sensors. Overall, the test results indicated the feasibility of using the optical fiber sensor-embedded strands as a reliable means for monitoring PT tendons of in-service bridges.
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