Monitoring of structural prestress loss in RC beams by inner distributed Brillouin and fiber Bragg grating sensors on a single optical fiber

For the safety of a prestressed structure, prestress loss is a critical issue. Unfortunately, up to date, with consideration of the harsh environment and the durability, no qualified technique is available. This paper proposes a novel technique to monitor prestress loss in RC beams by using combined Brillouin and fiber Bragg grating sensors on a single optical fiber. A smart steel strand based on the newly developed sensor was introduced. Laboratory tests of a series of prestressed RC beams were used to verify the concept of monitoring of prestress loss by using the smart steel strands. The prestress loss obtained from the Brillouin and the fiber Bragg grating sensors are compared with those from the load cell and the structural analysis, which validated the feasibility of the proposed sensing system. The monitoring results from the proposed optical sensors can reveal both the spatial distribution and the time history of prestress loss during the construction and the in-service phase.