Prestressed fiber–reinforced polymer composites have gained popularity as a structural rehabilitation technique; however, the prestress loss remains a critical issue in terms of material efficiency and structure safety. This article presents a fiber Bragg grating–based technique for prestress loss monitoring in reinforced concrete beams strengthened by prestressed near-surface mounted carbon fiber–reinforced polymer strips. Bare fiber Bragg grating sensors are used to monitor the time history of the prestress loss in near-surface mounted strips with different prestress levels during both the construction stage and the ultimate loading phase. The prestress losses measured by the fiber Bragg grating sensors are further compared with the data reported by the conventional electrical strain gauges. The results show that the fiber Bragg grating sensors can effectively monitor the prestress loss when properly integrated into the near-surface mounted strips. They also provide a reliable method for crack damage detection in concrete.
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