基于POF-OTDR的混凝土坝裂缝监测复用能力分析
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摘要
塑料光纤由于弥补了石英光纤容易断裂的缺点,且具有大直径、低成本、高可塑性、良好韧性等优良特性,在结构裂缝监测领域具有良好的前景.将塑料光纤应用于以混凝土坝为代表的大体积混凝土结构裂缝监测时,不仅要求其能够感知单条裂缝的产生,更需要其具有对结构多处开裂的感知和持续监测能力.为了研究塑料光纤对混凝土结构多条裂缝的监测能力,设计了一套模拟结构出现不同角度裂缝的试验装置,采用光时域反射技术进行了力光转换特性试验,并利用试验结果推导了单支塑料光纤对裂缝监测的复用能力.试验结果显示,塑料光纤对裂缝开展的感知敏感性随塑料光纤与裂缝的夹角和裂缝开度的增大而降低.理论分析表明,塑料光纤的复用能力和敏感性之间存在相互制约关系,即塑料光纤与裂缝夹角较大时,敏感性较大,而复用能力较小,反之亦然.基于以上分析,以某混凝土坝为例结合两种不同敏感程度的布设方式计算了各坝段开裂情况对光时域反射动态范围的消耗量,验证了以上结论,并对塑料光纤在混凝土坝中的实际裂缝监测能力进行了探讨和评估.分析表明,塑料光纤虽具有较好的裂缝监测复用能力,为避免出现裂缝漏检的情况,实际应用中建议首尾两端探测和分坝段布设多条塑料光纤.
It is widely accepted that plastic optical fiber will have a broad application in the field of crack monitoring.Unlike the optical fibers of silica,this fiber is not easy to break and enjoys the advantages of large diameter,low cost,high plasticity,and good toughness.In the application of plastic optical fibers to crack monitoring of mass concrete structures like concrete dams,not only is the capacity for single crack sensing needed,but also the capacity for sensing and continuous monitoring of multiple cracks.In order to investigate the monitoring ability of plastic optical fibers for concrete structures with multiple cracks,a device which is capable of monitoring different angles between fibers and cracks was designed,and optical experiments using an optical time domain reflectometer were carried out.The crack monitoring multiplexing capability of single plastic optical fibers were then analyzed based on the experimental results.The results showed that the sensitivity of plastic optical fibers in terms of crack propagation decreases with increased angle and crack width.Theoretical analysis indicated that there is a constraint between multiplexing capability and sensibility of plastic optical fibers,i.e.,when the angle between plastic optical fiber and crack was great,the multiplexing capability was high while the sensitivity was low,and vice versa.Based on the above analysis,a concrete dam was studied as an engineering example.Specifically,in consideration of two design layouts,optical loss of plastic optical fibers resulting from cracks was calculated for each dam part.Actual monitoring ability of the plastic optical fibers in the dam is discussed and evaluated.Fibers with both ends showed superiority in real application and,in the process of avoiding missing inspection multiples,offered the good multiplexing capability of the single plastic optical fiber.
It is widely accepted that plastic optical fiber will have a broad application in the field of crack monitoring.Unlike the optical fibers of silica,this fiber is not easy to break and enjoys the advantages of large diameter,low cost,high plasticity,and good toughness.In the application of plastic optical fibers to crack monitoring of mass concrete structures like concrete dams,not only is the capacity for single crack sensing needed,but also the capacity for sensing and continuous monitoring of multiple cracks.In order to investigate the monitoring ability of plastic optical fibers for concrete structures with multiple cracks,a device which is capable of monitoring different angles between fibers and cracks was designed,and optical experiments using an optical time domain reflectometer were carried out.The crack monitoring multiplexing capability of single plastic optical fibers were then analyzed based on the experimental results.The results showed that the sensitivity of plastic optical fibers in terms of crack propagation decreases with increased angle and crack width.Theoretical analysis indicated that there is a constraint between multiplexing capability and sensibility of plastic optical fibers,i.e.,when the angle between plastic optical fiber and crack was great,the multiplexing capability was high while the sensitivity was low,and vice versa.Based on the above analysis,a concrete dam was studied as an engineering example.Specifically,in consideration of two design layouts,optical loss of plastic optical fibers resulting from cracks was calculated for each dam part.Actual monitoring ability of the plastic optical fibers in the dam is discussed and evaluated.Fibers with both ends showed superiority in real application and,in the process of avoiding missing inspection multiples,offered the good multiplexing capability of the single plastic optical fiber.
引文
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[3]Zhao J,Bao T,Chen R.Crack monitoring capability of plastic optical fibers for concrete structures[J].Optical Fiber Technology,2015(24):70-76.
[4]包腾飞,李涧鸣,赵津磊.表面粘贴式塑料光纤与混凝土间应变传递模型及敏感性分析[J].水利水电科技进展,2018,38(5):59-64.Bao Tengfei,Li Jianming,Zhao Jinlei.Modeling and sensitivity analysis of strain transfer between surfacebonded POFs and concrete[J].Advances in Science and Technology of Water Resources,2018,38(5):59-64(in Chinese).
[5]Zhang C,Zhu H,Shi B,et al.Performance evaluation of soil-embedded plastic optical fiber sensors for geotechnical monitoring[J].Smart Structures and Systems,2016,17(2):297-311.
[6]包腾飞,赵津磊,李涧鸣.剪扭作用下塑料光纤力光转换特性试验研究[J].光子学报,2018,47(4):219-226.Bao Tengfei,Zhao Jinlei,Li Jianming.Experiment of optical response characteristics of plastic optical fibers under shear and torsion loading[J].Acta Photonica Sinica,2018,47(4):219-226(in Chinese).
[7]吴永红,刘龙江.裂缝方位对大坝裂缝光纤监测复用能力的影响[J].长江科学院院报,2007(1):20-22.Wu Yonghong,Liu Longjiang.Effect of crack orientation’s randomness on multiplexing capability of distributed fiber optic concrete dam crack detection[J].Journal of Yangtze River Scientific Research Institute,2007(1):20-22(in Chinese).
[8]吴永红,苏怀智,高培伟.混凝土大坝裂缝光纤监测关键性基本问题的协同研究[J].水力发电学报,2007(4):120-123.Wu Yonghong,Su Huaizhi,Gao Peiwei.Integrated study on key basic problems of fiber optic monitoring cracks in concrete large dams[J].Journal of Hydroelectric Engineering,2007(4):120-123(in Chinese).
[9]吴永红,苏怀智,徐洪钟,等.混凝土高坝裂缝光纤分布式监测能力的研究[J].光子学报,2007(4):722-725.Wu Yonghong,Su Huaizhi,Xu Hongzhong,et al.Study on multiplexing capability of huge concrete dam crack distributed fiber opptic monitoring[J].Acta Photonica Sinica,2007(4):722-725(in Chinese).
[10]钱飞,佟剑杰.混凝土坝裂缝分布式光纤监测复用能力研究[J].水电能源科学,2010,28(1):70-72,109.Qian Fei,Tong Jianjie.Study on multiplex capacity of distributed optical fiber monitoring for cracks of concrete dam[J].Water Resources and Power,2010,28(1):70-72,109(in Chinese).
[11]Liu J,Zhang J,Li X,et al.Study on multiplexing ability of identical fiber Bragg gratings in a single fiber[J].Chinese Journal of Aeronautics,2011,24(5):607-612.
[12]王惠文,江先进,赵长明,等.光纤传感技术与应用[M].北京:国防工业出版社,2001.Wang Huiwen,Jiang Xianjin,Zhao Changming,et al.The Technologies and Application of Optical Fiber Sensing[M].Beijing:China National Defense Press,2001(in Chinese).
[13]谢孔利.基于φ-OTDR的分布式光纤传感系统[D].成都:电子科技大学,2008.Xie Kongli.Distributed Opric-Fiber Sensing System Based on?-OTDR[D].Chengdu:University of Electronic Science and Technology of China,2008(in Chinese).