| Bridge structure is the hub of transportation systems. With the development of large Bridges which has more and more structure, bringing huge economic benefits the crash risk is also increasing. It is necessary to take scientific evaluation approach to monitor the health of bridge health. Bridge monitoring can give bridge management advice of maintenance, which ensures the safety and normal use of the bridge. This paper puts forward a kind of optical fiber sensing technology based on the Sagnac interference to study the status of bridge health and the structural arrangement of this optical sensor is simple and it has high accuracy and wide application.This is the first time combined the Sagnac optical fiber sensor technology with the dynamic method of measurement for bridge natural frequency. In this paper, it establishes a simple optical fiber sensing model and axle vibration model, which can measure the natural frequencies of the bridge and analyze the status of bridge. Firstly this paper expounds the working principle of Sagnac interference sensor and designs one demodulation method, which was simulated and analyzed, and it shows us the Sagnac interference can demodulate the original signal in the ideal case. Secondly it carries out a detailed theoretical derivation and analysis for the axle model and the natural frequency measurements. And it proposed a method of bridge natural frequency identification. And it analyzes the influence of different modulus, rotational inertia, spring rate on natural frequency. And it concludes that the natural frequency can be regarded as the standard evaluation of bridge health. Then it designs and studies the LD module and PD module specifically. In the end, the paper plans out a test pattern which is the basis of the later simulation and the field experiment. And it concludes by the analysis of the simulation that the Sagnac fiber optic sensing technology can measuring the natural frequency of the bridge and monitoring the health of the bridge. |
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