Post-tensioning Force Measurement Using Optical Fiber Sensor-Embedded Strand for Prestressed Concrete Structures

Monitoring tendon forces of in-service post-tensioned concrete elements is important for understanding the health of the structures and evaluating the condition of prestressing strands. Current methods for determining the tendon forces of in-service structures have limitations in terms of simplicity, reliability, or durability and often provide measurements only at discrete locations. Investigations into alternative technologies to evaluate post-tensioning tendon forces for the health monitoring of prestressed concrete structures are needed. When installed along the length of post-tensioned tendons in concrete structures, optical fiber sensors provide a promising means to overcome the existing challenges of tendon force measurement. Prestressing strand that incorporates optical fiber sensors along the length of the strand has been developed by embedding the fibers in epoxy coating. The strands use Brillouin optical time domain reflectometry (BOTDR) to measure strain along the length of the entire strand. A research program is underway to evaluate the accuracy and reliability of strain data acquired from the optical fiber sensors and to develop a knowledge base needed for widespread field implementation. This paper describes tensile tests conducted on the prestressing strand that allow the assessment of strain acquired from the optical fibers using BOTDR. To date, the experiments have given promising results for the ability of the optical fiber sensors to provide reliable strain data that could be acquired during the service life of structures. Test results are presented along with a discussion of ongoing research and possible widespread deployment of the technology.