Research On The Dynamic Deflection Monitoring And Damage Identification Of Bridge Based On The Distributed Strain Sensing Technique

In the recent decades,the concept of structural health monitoring and as-related techniques have been popularized and developed in the field of civil engineering,which contributes a lot to the bridge disease prevention and monitoring.Health monitoring technology is in the ascendant in China,the most representative and pervasive of which is the accelerometer based dynamic diagnosis technique.This type of technology envisages structural damage affects dynamic parameters such as frequency,mode and frequency response function;however,these indicators are too macroscopic to be insensitive to the local damage.As a supplementary static diagnosis technology,point sensors such as strain gauges and displacement gauges are mainly used,which are not quite suitable for the concrete civil engineering due to their small coverage.The distributed monitoring can be realized by the long-gauge optical fiber strain sensors,which not only solves the fragile environmental adaptability of the bare optical fiber,but also integrates the excellent anti-electromagnetic interference capability of the optical fiber itself.Moreover,it can not only detect small local damage,but also reflect macroscopic structure information.This paper will discuss and develop two types of health monitoring technologies based on distributed long-gauge strain sensors,including dynamic deflection monitoring and damage identification.The specific advantages of this type of sensor are demonstrated through this work.The research contents and main conclusions are as follows:(1)This paper introduces two kinds of deflection inversion methods based on the beam deformation theory,including conjugate beam method and quadratic integral method,both of which adopt strain inversion deflection method.In this paper,they are combined with distributed long-gauge strain(macro strain)and extended to continuous beam,Timoshenko beam,box girder and other beam Bridges.Finally,the fitting accuracy of the two methods in a variety of scenarios is discussed by means of numerical simulation.It can be found that both methods have high accuracy and excellent anti-noise ability in simulating Euler-Bernoulli beam.The fitting deflection curve of continuous beam by quadratic integral method must be fitted by span,while the conjugate beam method can be used to fit them directly.The improved quadratic integration method can reduce the deflection inversion error caused by shear deformation to a great extent.The conjugate beam method is not so effective,but it also reduces the relative error by 20%compared with the method without considering the influence of shear deformation.The shear lag effect of box girder does not have much impact on the accuracy of the two methods.(2)The deflection inversion method based on modal analysis theory is introduced.The basic theory of point strain modal analysis is generalized,and then extended to the theory of macro strain modal analysis.The displacement strain transfer function(DST)is extended to the displacement macro strain transfer function(DMST).The method of using DMST matrix to invert dynamic deflection is proposed,and the relationship between the macro strain mode and displacement mode is introduced.Finally,the theoretical method is tested by the simulation test,and the following conclusions are drawn:Taking the mass normalization as the standard of vibration mode,the displacement mode can not get the accurate normalized macro strain mode,and the precision of the extended displacement mode of the macro strain mode is higher,but the precision of the inverse displacement mode of the macro strain mode after the noise pollution will reduce a lot;The conjugate beam method is not as good as the modal matrix function method in fitting dynamic deflection,,including the DMST matrix method and the displacement rotation transfer function(DRT)matrix method,and only the first three modes are needed to achieve the accuracy requirements;The modal matrix method is theoretically applicable to any structure of bridge,and the DMST matrix can be used repeatedly,reducing the calculation consumption,but the noise resistance is not as good as the conjugate beam method.(3)Two damage identification methods based on long gauge strain influence line under moving load are introduced,including macro-strain envelope method and macro-strain time history area method.In order to simulate the real scene,this paper also introduces the steps and theoretical basis of using ABAQUS to establish the vehicle bridge coupling model considering the road roughness,and uses the model to verify the damage identification method.In the numerical simulation test,the influence of different factors on the two damage identification methods are discussed,including speed,axle load,number of axles,multi damage structure,etc.It is found that the performance of macro strain envelope method is not as good as that of macro strain time history area method in two important indexes of damage location and damage degree,and the latter can directly use the original strain,but the former can only be used after the static strain is obtained by signal processing technology.