| Deflection deformation is the linear displacement along the axis of the cross-section of the member in the direction perpendicular to the axis when the bending component such as a bridge undergoes bending deformation due to stress or non-uniform temperature changes.It can directly reflect the stress status of bridge components and is a key indicator for evaluating the health of bridge structures and analyzing potential damage to bridges.Whether in the process of bridge construction or in the stage of stable operation of bridges,deflection monitoring is of great significance.Based on the limitations of existing deflection monitoring methods and the new requirements of contemporary bridge deflection long-term monitoring,developing sensor technology and systems suitable for long-term real-time monitoring of bridge dynamic deflection is of great engineering practical value and academic research significance.In this article,the author first discusses the research background and significance of deflection monitoring,and summarizes the advantages and disadvantages of several common deflection monitoring methods.Based on the introduction of optical fiber sensors and plastic optical fibers in the system,we try to select plastic optical fibers with excellent light guiding ability,toughness,anti-interference ability and stability as sensing elements,and design and manufacture a butterfly based on the principle of intensity modulation Shaped optical fiber displacement sensor,and build a multi-point distribution,real-time online deflection monitoring system.The system senses the displacement state of the point to be measured through the change of the geometric shape of the butterfly-shaped sensing element,uses the optical power meter to measure the geometric change of the sensing element,and transmits it to a remotely connected computer to achieve real-time online multi-point synchronization of the bridge deflection monitor.The system provides a simpler,more reliable,and lower-cost solution for the long-term stability measurement of bridge deflection.The main research work and conclusions of the paper include:(1)The basic theory of optical fiber transmission is introduced,the principle ofoptical fiber macrobending loss and optical power modulation is analyzed,anda butterfly-shaped plastic optical fiber sensor element is designed based on this,and then the four-leaf rose with a geometric shape similar to the sensor elementis used The curve deduces the mathematical relationship between opticalpower loss and displacement.(2)Then the butterfly-shaped optical fiber displacement sensor is built andmanufactured by using light source,optical power meter,sensor element andother equipment,and the displacement calibration experiment is carried out.The results show that the correlation coefficient of the fitting curve of theoptical power loss and the theoretical formula in the displacement range of0-60 mm exceeds 0.99,the fitting effect is good,the initial measurementaccuracy of the sensor is 3.63%,and the output resolution is 4.12%.In addition,the analysis of the influencing factors of the sensor shows that thebutterfly-shaped plastic optical fiber sensing element with the initial widthD=12cm and the core diameter d=1mm has the best stability and performance.Under normal working environment(temperature-5 ?? 55 ?,humidity30%?85%),the working stability and adaptability of the sensor element arebetter.(3)Finally,the butterfly-shaped optical fiber displacement sensor is installed at thepoint to be measured on the simply supported beam,and the occurrence andtrend of deflection deformation are detected by the output optical powerchange,and compared with the LVDT and finite element calculation results.The experimental results show that the measurement results of the three arebasically similar,the maximum absolute error is only 1.5mm,and themaximum relative error is 3.64%,which is less than the requirement of 5% ofthe bridge engineering deflection measurement error. |
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