Monitoring of Bridges based on Long-gauge Fiber Bragg Grating:from Structural Deformation to Damage Identification
In order to solve the issue that small and medium-span(SMS)bridges cannot be effectively maintained by manual inspection,due to their large number and wide distribution,long-gauge FBG is utilized to establish sensing system.Based on the thought of attaining functions using one core,various health monitoring methods are developed,including structural deformation and damage identification.As a result,a SMS bridge monitoring system is constructed.Firstly,the theory of conjugated beam is modified to cooperate with long-gauge FBG.Combined with Timoshenko beam theory,a deformation monitoring method based on long-gauge FBG is proposed.Then,through refined consideration of shear lag effect in box girder,a prestressing indirect monitoring method based on plane section assumption is refined to establish a prestressing monitoring method utilizing long-gauge FBG.At last,through theoretical deduction,an influence line of long-gauge strain is obtained.With this basis,a damage index and an identification method were carried out using the area of long-gauge strain.As a result,a SMS bridge monitoring system was built.For validating three proposed methods,corresponding indoor experiments are designed and conducted.The results show that the proposed deformation monitoring method could effectively eliminate the error caused by shear deformation.The overall identification errors are less than 3％under various deformation conditions and beam dimensions.For prestressing monitoring method,all of its identification errors are round 5％.Compared with the method based on plane section assumption,the promotion of accuracy is evident;proposed damage identification method could successfully identify the damage location with designed damage degree under various vehicle speeds.In contrast,the accuracy for damage degree identification would be influenced by vehicle speed and damage severity,which is not ideal but still acceptable.The entire results initially proves the application potential of building a SMS bridge monitoring system based on a set of long-gauge FBG.However,further refinement of these methods is still required.
bridge engineeringstructural health monitoringlong-gauge FBGsmall and medium-span bridgesstructural deformationdamage identification
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