Damage Detection Method For Substructure Of Bridges Based On Vechicle Excitation With Variable Velocity

In the long-term operation of the bridge,its substructure can be affected by many unfavorable factors,which will induce different degrees of damage,directly affecting its service status,and threatening the safe operation of the bridge.However,the damage of the bridge substructure is concealed,increasing the difficulties of diagnosis.To overcome these disadvantages,the method based on the change rate of wavelet packet energy variance is proposed in this paper,using the dynamic responses of the bridge substructure under the vehicle braking load,and the validity is verified through numerical analysis.The main contents and conclusions of this paper are shown as following:1)Based on the vehicle-bridge coupling vibration theory,the dynamic analysis model of vehicle-bridge interaction system was established considering the interaction mechanism between bridge and vehicles with varying speed,and the computer code was written.Relying on a practical bridge,the influence factors such as surface roughness,the vehicle braking position,initial velocity,braking acceleration rise time,peak braking factor and vehicle weight on dynamic response of bridge piers were studied;and the variation laws of structural dynamic characteristic were analyzed under typical damage cases like support failure,piers crack and foundation scour.2)Based on the wavelet packet analysis theory,the damage diagnosis of bridge substructure under vehicle braking load was proposed.First,the dynamic responses of bridge substructure were collected;then the wavelet base type and the decomposition layers were determinated,and the damage detection index,Wavelet Packet Energy Variance Variation Rate(WPEVVR),was proposed based on wavelet packet energy.The theories frame and process of damage identification of bridge substructure based on the proposed index were established,and the simulation was carried out by MATLAB.3)Using a numerical method,the finite element model of the full bridge was established,and the effectiveness of the method was verified.First,WPEVVR was used to identify the damage location of typical damage cases like support failure,piers crack and foundation scour.Second,the influence factors including surface roughness,the vehicle braking position,initial velocity,vehicle weight and noise on damage identifications were studied.At Last,the function relationship between the WPEVVR of the measuring point and scour depth was established,and the scour depth can be directly caculated by the inverse analysis.