Damage Identification Of Beam-type Bridges Based On A Parked Vehicle

Structural damages can be identified by the changes in modal parameters which are obtained from the structural dynamic response.The most commonly used modal parameters for structural damage detection are natural frequencies and mode shapes.Compared with the mode shapes,frequencies are generally more attractive to be employed for damage identification as they possess the advantages of convenience in measurement,high accuracy,and high anti-noise capability.However,the order number of natural frequencies that can be used for damage identification in the actual test is very limited,thus it is difficult to obtain a unique solution with frequencies only in damage identification which is a typical inverse problem.Furthermore,the same damages at the symmetric position of the symmetrical structure will cause the same frequency change,which makes it difficult to detect the damage of the symmetrical structure by using the frequency information alone.Such limitations restrict the adaptability of the frequency-based damage identification method.In view of this,a two-stage damage identification strategy,i.e.,localization and then quantification is proposed in this study for bridges based on the frequency variation of a parked vehicle-bridge system.The main work and conclusions are as follows:(1)The finite element model(FEM)of the parked vehicle-bridge system is established,and the natural frequency of the system can be obtained by solving the eigenvalue equation.The phenomenon of frequency variation of parked vehicle-bridge system with the vehicle parked at different locations is illustrated numerically.(2)A damage location index(DLI)is defined by the frequency change rate of the vehicle-bridge systems with the vehicle located at different locations before and after damage.Then the DLI is applied to localize damage in beam-type bridges.Numerical examples indicate that the proposed DLI can detect single and multiple damages effectively.The effects of noise,uneven distribution of flexural rigidity and the number of parking positions on the effectiveness of the prosed DLI are also studied via numerical simulation.The damage localization stage makes full advantage of convenient measurement and high accuracy of natural frequencies,in which only the frequency information of the system before and after damage are required.(3)Based on the FEM of the parked vehicle-bridge system,the damage equation that relates the frequency based parameter changes of the system and damage severity is established via theoretical derivation.Thus the damage severity can be quantified by combing the damage equation and the measured frequency based parameters of the system.Numerical examples indicate that using the damage quantification equation(s)can quantify single and multiple damages with satisfactory accuracy.The effects of measurement noise and the uneven distribution of flexural rigidity on the effectiveness of the proposed method are also studied via numerical simulation.(4)Experimental study is conduced to verify the feasibility of the proposed damage identification method.Firstly the parked vehicle and beam-type bridge model are created.Then the dynamic response of the vehicle-bridge systems under ambient excitation is measured to calculate the frequencies of the system.Finally the damage is localized and quantified by the proposed two stage method.