Study On The Bridge Damage Identification And Monitoring System Based On Distributed Long-gage FBG Sensing

During the long-term operation,the civil engineering structure are subjected to increasing traffic volume,overload,steel corrosion,fatigue effect,material aging and other natural and human adverse factors,which will inevitably result in resistance reduction and damage accumulation,and even lead to catastrophic accidents.The structural health monitoring(SHM)technology emerge as the times require,and it has been constantly studied.The SHM can be used for real-time safety monitoring,damage identification and performance evaluation of infrastructure structures such as bridges,tunnels and other types of infrastructures.However,there are some issues in the monitoring process of traditional sensor technology,such as weak correlation between data and structural performance,difficulty in effectively capturing the micro damage and so on.Under this background,our research group developed the distributed long-gauge strain sensing technology,which solved the problem that traditional "point" type monitoring is difficult to identify the local damage.On this basis,the long-gauge FBG sensor with enhanced sensitivity and its standardized manufacturing method are developed.The method of moving load identification and structure damage identification are studied based on long-gauge strain influence line.Meanwhile,the deflection inversion method based on long-gauge strain are also studied.The main research contents and creative points are as follows:(1)The packaging method and standardized manufacturing technology of long-gauge sensitized FBG sensor are developed based on the distributed long-gauge sensing technology,and the design idea and sensitization theory of the sensor are discussed.The sensitivity coefficient and repeatability of the sensor are tested by static uniaxial tensile experiment,and the long-term stability of the sensor is tested by long-term performance test.Moreover,the strain sensing technology with temperature self-compensation is studied,which is aimed at the temperature compensation in practical engineering,and the performance of this method is tested.(2)The moving load identification method is established based on long-gauge strain influence line.Firstly,the expression of long-gauge strain influence line under moving load is derived on the basis of traditional strain influence line theory.The moving load is identified by using the relationship that the vehicle weight is proportional to the area of strain influence line.In addition,the identification methods of vehicle speed,wheelbase,vehicle weight and other parameters are studied,and the method is verified by finite element simulation and indoor experiment.(3)A damage identification method of box girder bridges is proposed under moving load.The difference of strain influence line(DSIL)is used as the identification index to characterize the structure damage.With the shear lag effect under consideration for the box girder bridges,the damage identification theory is derived based on long-gauge strain influence line.A regularized index DSIL is proposed for the identifications of damage location and extent.The effectiveness of the method is verified by numerical simulation,and a series of experiments are carried out to study the influences of speed,vehicle type and vehicle weight on the damage identification.In addition,the conjugate beam method is used to study the deflection inversion method based on long-gauge strain response.(4)The expression of deflection influence line of box girder bridges is derived under moving load.On this basis,a damage identification method based on deflection influence line is proposed,and the identification index is the curvature of difference of deflection influence line(CDDIL)before and after damage.The effectiveness of the method is verified through a series of finite element simulations and indoor experiments.(5)Starting from the composition of the monitoring system and the design ideas of software and hardware,the bridge health monitoring system is studied and discussed.Taking a variable cross-section continuous box girder bridge strengthened by external prestressing as the research object.The distributed optical fiber sensing system is used to monitor the safety of reinforcement construction process and the long-term operation status.