Preliminary Study On Vehicle Bridge Coupling Bridge Detection Method Based On Fusion Of Transmissibility And Stochastic Subspace Method

China,as a cradle of Chinese civilization with vast territory and abundant resources.Its bridge construction and development have a long history.Since the transition from a big bridge country to a powerful bridge country,bridge in-service condition assessment and follow-up operation and maintenance support have gradually become the research hotspot of experts and scholars.Based on the large number of bridges,the ratio of old bridge and dangerous bridge,and the complicated operation and high economic cost of traditional bridge detection methods,a bridge detection and evaluation method with strong mobility,high safety and economic applicability is urgently needed.Therefore,different from the direct acquisition of bridge structure vibration signal by sensors,the detection technology of indirectly collecting time history response signal by using simple and portable media such as test vehicle arises at the historic moment,and the bridge frequency is preliminarily extracted by this method.At present,the vehicle bridge coupling detection technology is not limited to the identification of the fundamental frequency of the bridge,and has achieved certain results in the identification of other bridge modal parameters and subsequent damage identification and bridge structural state assessment.In this paper,based on the traditional vehicle bridge coupling detection method,the operation mode of the special detection vehicle is adjusted.The power tractor is used to drag two special detection vehicles with fixed workshop spacing along the layout of the measurement points and stop at rest.After collecting the excitation signal of the measurement points,the operation is repeated until the detection vehicle passes through the whole bridge.Based on the time history response obtained by the detection vehicle,the time history response is transmitted between two points Based on the recurrence characteristics,the modal shapes of the bridge span are identified by the covariance driven stochastic subspace method,and the bridge health status is quickly evaluated.The main work and research results are summarized as follows(1)In the basic theory part,based on the two vehicle bridge coupling model,the vibration control equation and time history response relationship between the test vehicle and the bridge,as well as the contact point of the test wheel are derived,On this basis,the transmissivity expressions of two consecutive adjacent measuring points of bridge body response and vehicle bridge contact point response are derived from the perspective of frequency domain analysis to verify the feasibility of constructing the global first-order vibration mode of the bridge.At the same time,the random subspace method is introduced to identify the local relative vibration mode value of the bridge.Finally,the overall modal shape of the bridge is constructed by using the inference that the transfer rate between two points is not affected by external excitation and vehicle bridge damping,and the bending stiffness of the beam section is calculated by the improved direct stiffness method.Finally,the identification steps of vehicle bridge coupling bridge detection method are summarized in the form of flow chart,from the vehicle body time history response signal to the section bending stiffness.(2)In the part of numerical simulation,the flow chart of bridge detection in the theoretical derivation is simulated and verified in detail step by step,and then the time domain signal,frequency domain result,vibration mode and beam section bending result of the direct measurement method and the indirect detection method based on dual vehicle bridge coupling proposed in this paper are compared.The simulation results show that the identification result of the new detection method in this paper is close to that of the direct measurement method.In addition,aiming at the applicability of the new method in the actual engineering situation.On the one hand,the multiple correction method of pre-processing and the two-step method of post-processing are introduced to modify the data and optimize the results of damage identification;on the other hand,the influence of external excitation on damage location and bridge modal parameter identification is discussed by using factor control method.The results show that the method has good robustness under the influence of the above parameters and excitation.Finally,the preliminary numerical simulation research on bearing damage identification and highorder modal extraction is carried out.(3)In the part of real bridge test,the new indirect measurement method proposed in this paper is preliminarily verified.The car body signal is extracted by a specially designed uniaxial testing vehicle,and the first-order frequency and mode shape of the bridge are obtained successfully through the car body signal inversion of the vehicle bridge contact point signal.Further,the mid span deflection value and the section of the fourth span of the bridge to be tested are identified by the improved direct stiffness method The point stiffness value is used to monitor and evaluate the health condition of the bridge.