ABSTRACT
This paper presents a technical feasibility study on distributed fiber optic vibration sensing for bridge health monitoring applications. The distributed fiber optic sensing technology, which exploits phase change in Rayleigh backscattering light enables temporally continuous and real-time vibration measurements along the entire fiber optic cable. Fiber optic cables laid along public roads and highways could be utilized to monitor conditions of many bridges at a time, which is a major benefit compared with conventional point-sensing technologies. With regard to health monitoring methods, operational modal analysis is one of the useful approaches, which identifies modal parameters like natural frequency, damping ratio, and mode shapes from ambient vibrations of a bridge, where a shift in the modal parameters indicates change in health conditions. The point-sensing systems based on accelerometers are now widely used for modal parameter identification. On the other hand, since the distributed fiber optic vibration sensing is new, modal parameter identification still remains challenging due to fiber layout and attachment conditions in real scenarios. This paper investigates the feasibility of modal parameter identification using the distributed sensing and compares with modal parameters identified by acceleration signals, used as reference information. In a controlled experiment on a model bridge at in-house facility following results are obtained. a) Similarity in modal parameters between distributed vibration signals and point-sensing acceleration signals, and b) Shift of modal parameters from intact to damaged condition, where the damaged condition represent three saw cuts on both side of web plates of the model bridge.
