Fiber optical sensors have been the subjects of considerable research for the past 25 years, with initial applications in military and aerospace areas. The concept of using fiber optical sensors in concrete structures was first introduced in late 1980s. So far, a variety of fiber optical sensors have been developed to monitor the strain distribution, temperature distribution, crack propagation, and reinforcement corrosion condition in concrete structures....[ Read more ]

Fiber optical sensors have been the subjects of considerable research for the past 25 years, with initial applications in military and aerospace areas. The concept of using fiber optical sensors in concrete structures was first introduced in late 1980s. So far, a variety of fiber optical sensors have been developed to monitor the strain distribution, temperature distribution, crack propagation, and reinforcement corrosion condition in concrete structures.

In optical fiber sensing, the change in light properties is measured and the measurement is a direct indication of the deformation of the fiber. The deformation or damage stage of the structure to which the fiber sensor is attached can be obtained by the proper interpretation of results. Therefore it is essential to understand the transfer mechanics between the fiber and the structure. In this thesis, this important concept is illustrated through two different applications of fiber optic sensing in concrete structures. The development of a novel distributed crack sensor is first discussed. Cracks in a structure can be located by the OTDR system and the size of the cracks can be related to the optical power loss. Experimental testing has been carried out for different fiber types and orientations. Also a theoretical model had been developed to provide a guideline for the sensor design. Finite element method and wave propagation analysis are used in the model and the result shows good agreement with the experimental data. With the sensor, no prior knowledge of crack location is required and a small number of fibers can be used to monitor cracking in a large. Secondly, durability problems of fiber optic strain sensors are analyzed. A theoretical framework has been developed to quantify the effect of environmental conditions on the calibration shift of strain sensors based on interferometry or the Bragg grating. Based on the results, design guidelines to minimize calibration shift are identified.