Regional Distribution Monitoring Of Structures Based On Long-gauge Optical Fiber Sensing And Damage Identification

In the process of structural operation,all kinds of structures are subject to environmental erosion,material deterioration and various loads.The structural damage gradually generates,develops and even seriously threatens to the normal use and ultimate bearing capacity of the structures.Therefore,reasonable and effective structural health monitoring technology is an effective guarantee for early detection of structural damage and early warning of performance degradation.Rebar corrosion is one of the important reasons leading to the early damage of reinforced concrete structures.How to accurately obtain the corrosion information of rebars,including the location and area of corrosion,is the key to further evaluating the structural performance after corrosion.Bridge bearing damage is an important factor that affects the performance of bridge structures.Effective monitoring of bridge bearing damage is an important guarantee for the safe operation of bridge structures.In this dissertation,based on the long-gauge optical fiber sensing technology,the identification and evaluation methods of two types of diseases,rebar corrosion and bridge bearing damage,are proposed.Specific research contents are as follows:(1)This dissertation summarizes and analyzes the basic concept of long-gauge optical fiber sensing technology,the characteristics of long-gauge optical fiber sensors and the concept of regional distribution sensing.The regional distribution monitoring of the double-curved arch bridge of Nanjing Yangtze river bridge shows that the bridge is in good operation condition after maintenance and reinforcement.(2)Structural corrosion localization and quantification methods through the static load test and moving vehicle test are established based on the long-gauge optical fiber sensing technology.For the static load test,the ratio of long-gauge strain before and after corrosion and its logarithmic index are used to locate the corrosion.The areas of rebar after corrosion are inverted by the average element stiffness.For the moving vehicle test,based on the envelope area of the long-gauge strain history and its logarithmic damage index,the corrosion location are identified.The integrations of long-gauge strain time-history are used to identify the average stiffness of structural elements and further invert the area of rebars after corrosion.Different methods of corrosion quantification are proposed in the early and middle stages of corrosion.The finite element simulation and electrochemical acceleration experiments of reinforced concrete beams verified the effectiveness of the corrosion monitoring methods in the early and middle stages of corrosion respectively.(3)Based on the results of corrosion localization and quantification,the bearing capacity of the reinforced concrete beam after corrosion was evaluated.The equivalent rebar ratio and the equivalent rebar areas were used to modify the constitutive model of the corroded rebar.The bearing capacity of the reinforced concrete beam was predicted based on the modified constitutive model and the equivalent rebar areas.The comparative analysis of the actual bearing capacity performance and the prediction results measured by the destructive experiment of the corroded beams verified the accuracy of the bearing capacity evaluation results,and the damage characteristics of the corroded beams were analyzed and summarized.(4)Bearing damage is one of the main diseases of bridge structure and the key to the safe operation of bridge.In this dissertation,based on the the long-gauge optical fiber sensing technology,a bearing damage identification method of tied-arch bridge under the test of environmental vibration is proposed,including ’slope method’ and ’index method’.Both methods use the change modes of beam dynamic index for the indirect identification of bearing damage.The methods are easy to operate and can effectively distinguish different damage modes including bearing damage,element damage and tie damage.And the finite element software was used to simulate various damages of the laboratory tied arch bridge,which verified the accuracy of the methods.