| Ancient building as an important part of the world cultural heritage, is the important carrier of human civilization, and non-renewable resources. However, with the rapid development of society, modern urban construction, environmental pollution and the development of the tourism industry especially, health status of ancient building is not optimistic, so we must assess and monitor health status of the ancient buildings. Traditional monitoring technology of ancient buildings can’t realize distributed monitoring and assessment of all, especially for large ancient wall. This article obtains special requirements from the ancient building monitoring, and the distributed optical fiber monitoring method (DFOS) is applied to the Donghua Gate of the imperial palace, Beijing. Deformation and temperature of the wall is monitored, and the corresponding sensor is developed; on this basis, it mainly focus on the deformation and seepage of the wall and deformation of the doorway. The results are as follows:(1) The paper summarizes the research status and deficiencies of ancient building monitoring, introduces basic principle, technical index and scope of application of several kinds of optical fiber sensing technology, and analyzes the advantages and disadvantages of the traditional monitoring methods, this paper discusses the superiority of the distributed optical fiber sensing technique applied to ancient building monitoring.(2) Some pivotal technologies are studied in the process of the application of optical fiber sensing technology, including the performance of the three kinds of distributed optical fiber demodulation devices, optical fiber coupling deformation and error analysis of displacement, etc.; Carried out testing research on performance of the surface paste sensor and fixed-point fiber sensor, and developed some new type sensors for the deformation and seepage monitoring of ancient wall.(3) According to the particularity of ancient building monitoring, installation process of the sensor cable is developed:the wall of the sensor adopts fixed point technology, the installation of the sensors adopts surface paste installation, which ensure the effective transmission of stress and strain.(4) It established distributed optical fiber monitoring system of DongHua gate, Beijing. Monitoring data is obtained successfully in two years, the deformation and leakage of wall are analyzed totally, and two potential regions of leakage are located.(5) Distributed optical fiber monitoring results of the platform show that the two years of monitoring period, north wall is stability; But in the 2 to 3 months period of completion of the wall repair, the wall surface appeared compressive strain area, but was not sustainable development. The strain monitoring results of west wall show that the wall strain changes smaller and the wall is stable; But in the left shoulder, a slight tensile strain was monitored, and showed a trend of increase in the later period monitoring. The deformation of middle doorway was small, and the overall structure is of stability. Distributed temperature measurement results show that near 8 m,35 m, 48 m region of the wall appeared leakage.(6) Based on ANSYS software, heat-stress coupling of platform is analyzed. The results obtained temperature contours and strain contours under the maximum temperature and minimum temperature in one day of July and January, and strain diagram of temperature transformation with critical path. Extrapolating the wall cracks and weathering serious potential area, which can provide the basis for the walls repair for the protection of cultural relics department.It is showed in the thesis research results that the distributed optical fiber sensing technology applied in the monitoring of ancient buildings has showed great advantage and can be popularized as a kind of measurements which is all-around and refined. |
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