United States Department of Transportation
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Sensor-Assisted Condition Evaluation of Steel and Prestressed Concrete Girder Bridges Subjected to Fire – Phase III
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2023-07-01
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[PDF-3.23 MB]
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Edition:Final Report January 1, 2020 – July 30, 2023
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Abstract:This report summarizes the results and findings of Mid-America Transportation Research Center (MATC) research project No. 61706. It is focused on the measurement of strain and temperature in steel plates under high temperatures using a tunable-wavelength coherent optical time domain reflectometry (TW-COTDR) technique. The main objectives of this study are: (a) to experimentally investigate the effect of heat treatment on Rayleigh scattering based distributed single mode fiber optic temperature measurement; (b) to quantify Rayleigh scattering based measurement accuracy of distributed fiber optic sensors under a heating-holding load protocol and characterize the effect of polymer coating on the sensors as the polymer softens and melts away at elevated temperatures; (c) to experimentally and numerically investigate effectiveness and limitation of Rayleigh scattering based, distributed fiber optic sensors (DFOS) without coatings for measuring temperature and strain of a steel plate subjected to a local constant temperature. One-time heat treatment eliminates the hysteresis effect and stabilizes the Rayleigh scattering based fiber optic temperature measurement up to 1000 ℃. The typical dual-layer coating effect on the temperature sensitivity of the Rayleigh frequency shift can be neglected at high temperatures in civil engineering application. It is found that the DFOS accurately measured the temperature and strain of the steel plate with different bond lengths of the epoxy, as compared to the thermocouple temperature and thermal-induced strain, respectively. The maximum strain (or temperature) that the DFOS without coatings could measure for the steel plate was less than 1600 ???????? (or 150 ℃). The fibers attached on steel plates with epoxy function like an extensometer at 155 °C~267 °C as a center portion of the coating with the high-end temperature is melted.
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