Theoretical Solution And Application Of Asymmetric Two-Axle Vehicle For Bridge Inspection

The indirect approach for bridge,proposed by Yang et al.in 2004,is a novel ideal to collect the vibration data of bridge by a moving vehicle installed with a few sensors,the model parameters(frequency,mode shape,damping)and health condition of the bridge can be gained with some technologies,which is quite different from the direct approach.The indirect approach is expected to achieve rapid bridge inspection and significantly reduce the cost because of the advantages in convenience and application range,which has great development potential and wide application scenarios.A number of scholars have been attracted to the research and demonstrated the effectiveness and advantages of this method,since the concept of indirect approach was proposed.The moving vehicle is not only a carrier to record data but also an excitation for bridge,so different vehicle forms may cause different results.Compared with single-axle(Single-Degree-Of-Freedom)vehicle,the two-axle(Two-Degree-Of-Freedom)vehicle has characteristics of carrying more information,simple production process and self-driving,so the two-axle vehicle may be more suitable for indirect approach.This thesis mainly studies the theory and application of two-axle vehicle for bridge indirect approach.The main work of this thesis includes:(1)The model of interaction between TDOF asymmetric two-axle vehicle and simply supported beam bridge is established,and the theoretical solutions of the dynamic responses of the bridge and vehicle are derived by the two-stage method;(2)The finite element model of vehicle-bridge interaction(VBI)is established,and theoretical solution is compared with numerical solution to verify the validity of the theoretical solution;(3)Theoretical solutions of vehicle frequency and frequency response function(FRF)for the vertical and rotational motion coupled two-axle vehicle are derivation,and then have parameterized analysis of the influences due to changes of vehicle length,center of mass position,vehicle stiffness and excitation at contact points to vehicle frequency and FRF;(4)For ‘coupling and uncoupling’,‘resonance and cancellation’ in vehicle response and ‘beating vibration’ in contact point response,the mechanisms are studied by theory and carried out by numerical simulation;(5)Finally,the applications of two-axle vehicle in indirect approach for bridge were studied,including identifying bridge frequency,mode and damage.The influences of bridge roughness and measurement noise on the identification effect are also studied.Based on the above research work,the main conclusions of this thesis are as follows:(1)For two-axle vehicle,the vertical and rotational motions are generally coupled,but when parameters meet the conditions,the vehicle will turn uncoupled,and the forms of vehicle frequency and frequency response function theories will degenerate;(2)When the excitation frequency at contact point changes,there are always six forms of FRF,also one zero point and two singular points,which corresponding to the cancellation and resonance phenomena respectively;(3)In the TDOF asymmetric two-axis vehicle response,the influence of excitations from front and rear contact points cannot be eliminated at the same time;(4)When the vehicle frequency is equal to the bridge frequency,the system will resonate,but due to the short acting time and energy divergence,the resonance phenomenon in vehicle response is not fully developed;(5)In the bridge indirect approach,two-axle vehicle can be used to identify bridge mode parameters,and the bridge damage can be identified according to the correlation between front and rear contact point responses.