Bridge Dynamic Performance Monitoring And Damage Identification Methods Based On The Distributed Long-gauge Strain Sensing

The methods for bridge dynamic performance monitoring and damage identification under moving vehicle load are studied in this paper.It is a process of the interaction between the vehicle and the bridge,when the vehicle passes over a bridge.At the same time,the parameters of the vehicle(vehicle speed,vehicle weight and axle number)and the pavement irregularity of the road are considered necessarily.The distributed long-gauge strain sensing realize the region monitoring by using the Fiber Bragg grating sensor,which is used in health monitoring for large civil structures,especially bridge structure.The traditional "point" type of sensor is "too local" and the traditional displacement sensor and acceleration sensor is "too macro" to reflect the local damage information of structures;the distributed long-gauge strain sensing overcome this shortcoming and has a good performance in dynamic and static monitoring.Research status of the bridge damage identification methods based on moving vehicle load,signal processing and application of fiber Bragg grating sensing technology were investigated and surveyed through a large number of literature reviews.In this paper,the damage identification method for bridge based on the distributed strain sensing technology under a moving vehicle load is studied and the main research contents are as follows:(1)Designed and established an experimental platform of vehicle-bridge in scale of 1:10 for bridge damage identification.The scale of the various parameters of the model bridge is calculated according to the theory of dynamic similarity ratio during the process of design of scale model.Details of the construction of the whole model experimental platform and the matters needing attention are introduced in detail and provide reference for future related model experiment.(2)A damage identification method based on distributed long strain of long-gauge strain influence envelope under moving vehicle load is proposed.In this paper,the change regularity of the long-gauge strain influence envelope line of the bridge under moving vehicle load is studied,and a new method of bridge damage identification is proposed which combined the strain gauge line and the distributed long-gauge strain sensing technology.The long-gauge strain influence envelop line is extracted using EMD method.Strain influence envelope line is selected as the damage index which is directly related to the local element stiffness of bridges.This indicator can reflect the distribution of the element stiffness of the bridge span which can be used to find out potential stiffness degradation area,and provide reliable basis for bridge management and maintenance.(3)Studied a method for bridge stiffness monitoring and damage identification using spatially-distributed optical fiber sensors under moving vehicle loads.Firstly,the relationship between the element stiffness of the bridge and the long-gauge strain history is studied,which indicates that the element stiffness of the bridge can be expressed by a formula of the long-gauge strain history.The stiffness coefficient calculated by long-gauge strain histories and the coordinate of sensors was used to identify the damage extent.To verify the validity of the method for damage identification,a model test on the bridge-vehicle model was conducted,and the long-gauge strain history was obtained by a fiber Bragg grating(FBG)sensor.The model test results show that the method is feasible for bridge stiffness monitoring and damage identification.(4)Proposed a new damage identification method for continuous beam bridges based on distributed long-gauge strain sensing technology.First,the variation regularity of the long-gauge strain influence line of continuous girder bridges which changes with the location of vehicles on the bridge is studied.Then according to this variation regularity,a calculation method for the distribution regularity of the area of long-gauge strain history is investigated.Second,a numerical simulation of damage identification based on the distribution regularity of the area of long-gauge strain history was conducted,and the results indicate that this method is effective for identifying damage and is not affected by the speed,axle number and weight of vehicles.Damage can be identified in the monitored span without traffic confliction,and only the long-gauge strain histories under a moving vehicle are necessary and it can also be used to carry out long-term monitoring of the highway bridge.The area of the long-gauge strain histories is selected as the damage index.This indicator can reflect the distribution of the element stiffness of the bridge span which can be used to find out potential stiffness degradation area,and provide reliable basis for bridge management and maintenance.(5)Studied the dynamic performance monitoring technology of the super large span bridge based on the distributed long gauge strain sensing.The distributed long-gauge strain monitoring system has been installed on main channel bridge of the Su Tong Bridge.This paper introduces the construction technology of the whole monitoring system in detail,including the pre-construction preparation work,the construction process of the sensor positioning,sensor paste,sensor protection,and later landscaping,etc.This paper introduces the problems and solutions in the construction process,and provides the engineering experience for the similar bridge monitoring project.Finally,the long-gauge strain mode of the long span rigid frame bridge is obtained.