| With the rapid development of the national economy,the development of bridge construction as a hub project has made a significant advance.At the same time,the health of bridges has attracted widespread attention.At present,the number of bridges in China ranks first in the world.Considering the amount of old and dangerous bridges,a method of rapid detection and evaluation of bridges is necessary for satisfying mobility,economy,safety and applicability.The indirect measurement method of bridge fundamental frequency by using the vehicle-bridge coupling system based on the mobile vehicle running the test bridge has been verified in field test.By now,the indirect measurement method is no longer limited to the test of the bridge fundamental frequency,and more bridge parameters are identified and further damage identification has gradually developed.The new method mentioned in this paper is different from the traditional indirect measurement method.It requires the tractor to simultaneously drag the two test vehicles at a fixed distance,and stop to collect for a while,and then repeat the operation until the test vehicles pass through the span of bridge.Using the signals collected from the test vehicles,the transfer rate matrix of the span of bridge can be calculated;and then the first-order mode shape of the bridge by using the singular value decomposition can be identified.The bending stiffness of each element in the span of the bridge can be further reckoned.In this paper,the feasibility of the method is firstly explained theoretically.Then the numerical simulation analysis is carried out under the factors of bridge damping ratio,test vehicle damping ratio,noise and external excitation variation.Finally,a preliminary verification is carried out by field test.The main work done in this paper and the relevant research conclusions are summarized as follows:(1)Based on the vehicle-bridge coupling system,the vertical acceleration signals collected from the sensors on the two stationary test vehicles are used for analysis.Comparing the test vehicle signals and the contact point signals between the test vehicle tires and the bridge deck are respectively calculated to obtain the section bending stiffness of each element of the span of the bridge.The contact point signal between the test vehicle tire and the bridge deck is calculated indirectly by the test vehicle signal.In the whole process,the two test vehicles move synchronously to the measuring point at a fixed distance,and stop to collect the signal;and then move,stop again to collect the signal until passing all the measuring points on the bridge.For the collected vertical acceleration signals,the transfer rate between each measurement point can be calculated;and then the transfer rate function matrix of the whole span of the bridge can be established.Based on transfer rate function matrix,the first order mode shape of the span of the bridge can be further extracted by using the singular value decomposition.Finally,the bending stiffness of each element of the span of the bridge can be identified by using the improved direct stiffness method.(2)The transfer rate method for obtaining the mode shape and corresponding bending stiffness of each element based on the test vehicles signals,and the contact point signals are theoretical derived.(3)Based on numerical simulation,the effect of the proposed method under the influence of bridge damping ratio,test vehicle damping,external excitation variation(including road roughness and seismic wave as external excitation)and noise is analyzed.(4)The real bridge test consists of four parts.Through the forced vibration test,the basic properties of the test vehicles are fully understood.The transmission test proves that the vibration response signal of the bridge can be transmitted to the vehicle body,and the modal parameters of the bridge can be identified from the vehicle body response.The direct measurement method is used to identify the bridge frequency for verification of the test results of the field test.The indirect measurement method of field test is used to collect the acceleration signal of the test vehicles.The section bending stiffness of the bridge is calculated according to the procedure of step 1.(5)The results show that compared with the direct test method on the bridge,the new method has good maneuverability and is suitable for rapid test of large-area and large-area bridge clusters.Compared with the traditional indirect measurement method,the new method increases a little time,but the identification result is excellent.It is significant to promote the indirect measurement technology based on the vehicle-bridge coupling system in the application of practical engineering. |
