Integrated Fiber Optic Sensor for Condition Monitoring of Concrete and FRP Tendons

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INTEGRATED FIBER OPTIC SENSOR CONDITION MONITORING OF CONCRETE AND FRP TENDONS ABSTRACT 9900338 Fiber reinforced plastics (FRP) have been employed as an alternative to conventional steel reinforcement in concrete structures. The primary attributes of FRP tendons are that of corrosion resistance reduced mass, and high tensile strength. Despite the much higher strength to weight ratios exhibited by FRP tendons, there are a number of drawbacks that hinders their widespread usage. In compare to the ductile elasto-plastic behavior of conventional steel reinforcement, the stress-strain response of FRP composites exhibit brittle behavior and are linear-elastic all the way to failure. This issue effects serviceability, design and safety of FRP tendons in concrete elements. This research program will focus attention into the development of an integrated fiber optic sensor system for condition monitoring of FRP bars. The sensor will comprise of an optical fiber with embedded partial reflectors along its length. An Optical Time Domain Reflectometer will be employed for interrogation of reflected optical signal from various regions of the structure. The fiber optic sensor system will be developed through a comprehensive research program during which the following issues will be addressed: (1) Practicality in terms of sensor confriguration for embeddment in concrete structures and simplicity of instrumentation during the condition monitoring stage. (2) Capability for seimulations detection of fiber breakage, its location, and measurement of strain gradients along the length of the member in a distributed manner. (3) Sensitivity in terms of strain amplitude and spatial resolution for characterization of damaged zone locations along the length of the FRP tendon. (4) Ruggedness for long term use during the life cycle of the structure. Performance of the proposed fiber optic system will be evaluated through an extensive experimental program involving quasi-static as well as fatigue loading of post-tensioned FRP beams. The efficacy of optical fibers in detecting, locating and evaluation of progressive damage will be investigated. A major portion of the project will involve evaluation of the system performance in terms of simultaneous detection of cracks emanating from different locations in beams. Tests will be performed to determine the level of confidence that can be achieved in correlating the fiber optic data for early detection of cracks in the FRP tendons as well as the surrounding concrete. The embedded optical fiber sensor will play a dual role. It will be employed for condition monitoring of the structure in real-time and to warn of impending failures, and for establishment of a comprehensive database pertaining to the material and structural behavior and therefore facilitate development of more realistic designs of FRP structures.