Modal Identification And Damage Detection Of Bridges Based On Mobile Intelligent Monitoring

Bridges are the key points and throats of national transportation lifeline project,which play an irreplaceable role in ensuring material transportation,promoting personnel communication and economic development.With more and more bridges serving longer and longer,the health conditions of bridges becomes more and more serious due to a series of unfavorable factors such as material degradation,overloading and so on.Once the bridge accident occurs,it will cause a large area of traffic paralysis and huge property losses,and even the loss of people's lives and serious social impact.At present,there are 594,600 road bridges serving for more than 10 years and 52,880 railway bridges serving for more than 13 years in China.However,the traditional bridge health monitoring method is difficult to meet such a huge health monitoring needs,which requires a rapid and efficient monitoring method.Therefore,intensive study of vehicle scanning method(VSM)shows important practical significance in promoting the development of bridge health monitoring technology,reducing the cost of bridge health monitoring,expanding the scope of bridge monitoring and achieving rapid monitoring.Based on current researches on bridge modal identification and health monitoring by direct method,and research progress and demand of vehicle scanning method,this thesis deeply studied the theory and method of identifying bridge frequencies,models,damping and detecting damages by a moving intelligent test vehicle.Some progress has been made in improving the performance of modal identification and damage detection by the vehicle scanning method in this thesis.The main contents and innovative achievements of this thesis are as follows:(1)The response of the contact point of the vehicle with the bridge,rather than the vehicle itself,is firstly proposed for modal identification of bridges.The closed-form solutions are derived for the vehicle and contact-point responses,and the computing approach for obtaining the contact-point response from vehicle response is presented.It is explained theoretically why the contact-point response is born to be free of the vehicle frequency and frequency response function(FRF)of the vehicle,which is also verified by finite element method.Based on the results of study,the contact-point response is recommended to be the better measurement for bridge modal identification in the vehicle scanning method.(2)An effective means for damage detection of bridges using vehicle scanning method is proposed.The component analysis of contact-point response is carried out theoretically.The instantaneous amplitude squared(IAS)of the driving component is calculated by the Hilbert transform,making use of its narrow-band feature.The IAS peaks serve as the key parameter for damage detection.The influence of various factors on the damage identification is also studied.Finally,the efficiency and robustness of the method are verified by simulation.(3)The concept of modal identification for bridges by two-axle test vehicle is proposed in this thesis.The coupled and closed solution of the vertical and rotational response of asymmetric vehicle are firstly obtained.From vehicle's frequency response functions(FRFs),various phenomena are explained,including coupling,uncoupling,resonance,cancellation and beat.The asymmetric vehicle-bridge-interaction(VBI)element with ten degree of freedom is also firstly derived in this thesis.The two-axle vehicle is successfully used to acquire the dynamic parameters of bridges.(4)A theoretical framework is presented for identifying the damping ratios of bridges using a two-axle moving test vehicle and verified by numerical simulation.The closed-form solution of scanning points are derived and the discrete form for field applications is given.By utilizing the attenuation nature of damping,the method to identify bridge damping is found from the bridge frequencies related components.By multiple condition studies,it is considered that the proposed method can identify bridge damping well and show strong robustness.(5)Some viewpoints and ideas in this thesis are verified through field experiments.The parameters of a same bridge are identified by the traditional direct method and the vehicle scanning method,respectively.The feasibility of transmission performance and contact-point response of test vehicle is verified.The bridge frequencies is successfully extracted from the moving test vehicle.The future experimental research is prospected.