Research On The Line-shape Measurement Method Of Bridge Structure Based On Fiber Optic Inertial Sensing

The bridge is an important infrastructure of national transportation. There aremany inspection methods to assess the bridge structural safety. According to therelevant industry standards of our country about "Standards for Technical ConditionEvaluation of Highway Bridges" and "Specification for Inspection and Evaluation ofLoad-bearing Capacity of Highway Bridges", the line-shape of the bridge structuralgeometry is one of the most important parameters of the bridge health status.According to the line-shape measuring result of the bridge structure, the changes ofinternal force can be inversed. The reliable conclusion of the health situation of thebridge structure can be provided.There are a large number of bridges in our country, so the bridge structural safetyinspection is a heavy work. Currently the main line-shape measurement methods ofthe bridge structural geometric are completed by the theodolite, total station, level andso on. Although the precision of these measurement methods is very well, there are alot of problems in applications. Those measurement methods of the bridge structuralgeometric line-shape need setting up the permanent reference points, erection ofequipment, determining measurement points. Those measurement methods will spenda lot of measuring time, so they are not fit the line-shape measuring for a hugenumber of small and medium bridges. The GPS measurement method can get thegeometric line-shape of bridge structure rapidly, but the precision is not good enough.Also the measuring signal will be disturbed easily by the cables and towers of bridge.According to the above analysis, researching a measurement technology with thehigh-efficiency and high-precision for line-shape measuring of bridge structure,getting the deformed position and deformation quantity rapidly and exactly, become achallenging research topic with great significance and application value.In the field of the inertial measurement, inertial instruments can accuratelymeasure motion parameters of carrier. The trajectory of carrier will be got by theintegration calculating. According to this feature, the fiber optic inertial sensingtechnology can be used to measure the line-shape of the bridge structural geometry.The bridge structural safety situation will be inspected. However, comparing to the field of inertial navigation, the application environment of the fiber optical inertialsensing technology has changed greatly, so the application method is different too.First, the measurement distance of INS (Inertial Navigation System) is very long.It is several tens of kilometers or even thousands of kilometers. But the measurementdistance of bridge structure is shorter.Second, the line-speed of INS is very fast. However, the measurement speed ofbridge structure line-shape is slow, and less demanding.Third, the measurement track of INS is random and non-repeatable, but theline-shape of bridge structure is a fixed curve. The measurement can be repeated.According to the above analysis, the line-shape measurement of bridge structuralgeometric is a special application field. There are some new technical requirementsfor the fiber optical inertial sensing in this application field.In order to inspect the security situation of bridge structure, the measurementaccuracy will be required to achieve a high level such as millimeter or less. However,this is very hard to achieve this level for INS. The line-shape of the bridge structuralgeometry is a shorter, fixed curve, so, the core content of this paper is that designing ameasurement method for geometric line-shape based on fiber optic inertial sensingtechnology, achieving accurate measurement for the short and fixed curve. Themethod will be used to measure the line-shape of the bridge structural geometric,improving the accuracy of measurement results to fit the requirements of the bridgestructure safety inspection.This paper has discussed the line-shape measurement method of bridge structuralgeometric based on fiber optical inertial sensing including the basic principles,application design, experiment analysis and applications. The main contents arefollowing.First, through the summary and analysis of existing line-shape measurementmethod of bridge structure, discussing the problems in the present. Researching onthe line-shape measurement method of bridge structure based on fiber optic inertialsensing, the existing problem of the line-shape measurement of bridge structuralgeometry will be solved.Second, the theory has been researched about the line-shape measurementmethod of bridge structural geometry based on fiber optic inertial sensing. On the basis of the theory, the collection methods of motion parameters about carrier aredetermined and the measurement system has been constructed. Using the line-shapemeasurement system to get the preliminary measurement result, the result of theline-shape measurement Analysis of line-shape measurement results has beenanalyzed. The error of the preliminary line-shape measurement result is large. Inorder to reduce the line-shape measurement error, the cause of error is analyzed. Theline-shape measurement error is mainly from the common influence from the internalfactors of the measurement system and the external factors of applicationenvironment. On this basis, the key technical of the line-shape measurement methodof bridge structure based on fiber optic inertial sensing has been determined.Third, researching the influence from the internal factors on the measurementsystem, these internal influence factors are determined mainly by the inherentcharacteristics of FOG and the carrier movement institute. The output signal of FOGhas been analyzed and the appropriate treatment and measures have been taken. Themore accurate movement parameters of FOG carrier will be obtained. Theapplicability and accuracy of line-shape measurement method will be better. Thedivergent error will be treated from the source.Fourth, researching the influence from the external factors of applicationenvironment on the measurement system, these external influence factors aredetermined mainly by the unsmooth pavement of bridge. The unsmooth pavement ofbridge will cause the vibration and shock of the FOG carrier. So the measurementsignal will contain noise error. The impact from the two different external stimulus onthe measurement results will be studied. Depending on the response mechanism,some different ways have been used to reduce the impact from the vibration andshock errors, improve signal to noise ratio of the measured signal.Fifth, the line-shape of the bridge structural geometry is a short and fixed curveand the curve can be measured repeatedly several times. The treatment method oferror will be designed, such as coordinate transformation, curve fitting by fixed point,error correction by the calibration bridge, mathematical statistics. The measurementerrors will be effectively deal with. The affect of the Earth’s curvature on themeasurement results will also be solved. The accuracy of the line-shape measuringresults will be improved, arriving at the millimeter level below. Sixth, the application of the line-shape measurement method of bridge structurebased on fiber optic inertial sensing technology has been researched and discussed.Analyzing and comparing the line-shape measurement results from the periodicmeasurement of the bridge structural geometry, the deformed position anddeformation quantity of the bridge structure will be got and the down-warping of thebridge structure will be determinate. The bridge structural safety situation will beinspected by this way. Analyzing and comparing the line-shape measurement resultsfrom the bridge structural loading or unloading. Analysis and comparison linear, thestrength, stiffness, stability and durability of the bridge structure will be assessed.From the actual application results of two methods, the line-shape measurementmethod of bridge structure based on fiber optic inertial sensing can inspect bridgestructural safety. Comparing to the other inspection methods, it has a great advantageof application.According to the research of this paper, the line-shape measurement method ofbridge structure based on fiber optic inertial sensing has a great advantage ofapplication such as high speed, high accuracy, good repeatability, high reliability, noneed to seal the bridge, no need to set up and protect the permanent reference point.Therefore, it has the broad application prospect.