Condition Evaluation of Precast Post-tensioned Concrete Girder Bridges During Fires from Distributed Fiber Optic Sensors

"In the past few years, the research team has instrumented three full-scale concrete slab on steel beam composite floor specimens with distributed fiber optic sensors using pulse pre-pumped Brilliouin optical time domain analysis (PPP-BOTDA). Cost-effective single-mode optical fibers were used as distributed sensors for strain measurements when not sheathed with protective layers and for temperature measurements when sheathed with protective layers. Each specimen was prepared in the National Fire Laboratory and tested under combined mechanical and thermal loading by the National Institute of Standards and Technology. Technical challenges discovered during data process and analysis include: (1) uncertain interfacial bond condition between optical fibers and their surrounding concrete as fire gradually melts or burns off the protective layers of the fibers, (2) slow measurement process (e.g., 2 minutes) for the understanding of fire dynamics effect, and (3) interactive effect of multiple cracks on strain and temperature discrimination. This project aims to further understand the behavior of interfaces between optical fibers and their surrounding concrete with or without the effect of protective layers, reduce measurement times using the concept of compressive sensing, and develop and validate the distributed sensing approach for monitoring of the prestress loss in grouted and non-grouted steel tendons in post-tensioned concrete girders under fire conditions. The scope of work includes (1) Effect of the protective layers and deployment schemes of a temperature sensor on potential binding of the optical fiber with its surrounding concrete at high temperatures, (2) Detectability of interactive concrete cracks from distributed strain sensors, (3) Rapid monitoring of the prestress loss in steel tendons in concrete girders, and (4) Implementation and validation of distributed fiber optic sensors in a large-scale two-girder supported bridge deck under combined dead load and fire conditions."

This project aims to further understand the behavior of interfaces between optical fibers and their surrounding concrete with or without the effect of protective layers, reduce measurement times using the concept of compressive sensing, and develop and validate the distributed sensing approach for monitoring of the prestress loss in grouted and non-grouted steel tendons in post-tensioned concrete girders under fire conditions. The scope of work includes (1) Effect of the protective layers and deployment schemes of a temperature sensor on potential binding of the optical fiber with its surrounding concrete at high temperatures, (2) Detectability of interactive concrete cracks from distributed strain sensors, (3) Rapid monitoring of the prestress loss in steel tendons in concrete girders, and (4) Implementation and validation of distributed fiber optic sensors in a large-scale two-girder supported bridge deck under combined dead load and fire conditions.

Implementation related data such as the effects of melting protective layers and sharp turns of optical fibers, measurement uncertainty and time in application settings, strain and temperature discrimination ability in the presence of multiple cracks, and field test and validation of the technology will be reported.

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