Study On Vibration Response Of Urban Bridge Under Vehicle Load

The structural vibration caused by urban traffic may not only damage the bridge itself,but also affect the human health around the structure.However,the vibration signal of this kind has a strong randomness,which cannot be described by determining the mathematical relationship,nor can it predict the exact value at a certain time in the future.In order to obtain the vibration response of the bridge structure under the action of traffic load,this paper carried out a study on the Bridges around Guangzhou Wanbo center,recorded the actual traffic flow,and recorded the vibration response of the bridge structure under various working conditions in detail.Then,the random traffic flow of the Liangang bridge and the Lirendong bridge was generated after screening the video data and analyzing the relevant data.Secondly,the response of bridge deck vibration under various working conditions(vehicle type,speed)is analyzed,and the vibration signal is simulated.Finally,the bridge model is built with ansys software,and the generated two-lane random traffic flow is used as the load input to analyze the vibration of the vehicle-bridge coupling system.The specific research contents of this paper are as follows:(1)To the collected traffic flow,it is divided into lanes 1 and lanes 2 and within each lane it is divided into five categories:car,minivan,truck,bus and trailer.Counting at intervals of five minutes,by summarizing the data,the total number of each model and the total number of vehicles in the testing period of the Liangang bridge and the Lirendong bridge were obtained,and then the proportion of each vehicle type in the total vehicle type and the distribution of lane 1 and lane 2 of each vehicle type are obtained.Divide 5 minutes by the number of each model within 5 minutes,and make a classification and summary to get the original data of time headway.Then the origin software is used to fit the time headway and obtain the function distribution according to the corresponding law.The results show that the time headway basic obedience one of Guass distribution,Log-Norma distribution,Lorentz distribution and the distribution of the ExtremeⅠ.Most of the fitting results were good,with the R~2value above 0.8,and many of the fitting results were excellent,with the R~2value above 0.99.After reading a large number of literatures,it is known that the vehicle weight follows a multi-peak normal distribution,so relevant information is searched and the probability distribution function of vehicle weight is obtained.A series of steps were carried out by Monte-carlo method,corresponding to lane 1 and lane 2 of the Lirendong bridge and the Liangang bridge,and the load-time curve of random traffic flow with the measured traffic flow characteristics was generated.(2)Time-frequency analysis was made on the vertical acceleration time-history curves of the bridge under various working conditions(cars,small trucks,large trucks and buses under 20km/h,40km/h,60km/h)and the measured mixed traffic flow.The results show that the maximum acceleration increases with the increase of vehicle weight and vehicle speed.Under various working conditions,the measured maximum acceleration of the Lirendong bridge is more than 6 times that of the Liangang bridge.The frequency distribution of the former is mainly between 10 and 60Hz,while the frequency distribution of the latter is mainly between 10 and 40Hz,indicating that the vibration response of Lirendong bridge is much stronger than that of Liangang bridge.Method at the same time,the introduction of artificial simulation of seismic wave superposition(trigonometric series method),by means of fast Fourier transform(FFT),the vertical acceleration of bridge under the action of different models,to simulate the schedule and corresponding to the time node of the generated random traffic flow,the corresponding single models under the action of bridge deck acceleration time history in the corresponding time node,generate 20 minutes of mixed traffic flow under the action of bridge deck acceleration time history,and compared with measured data and analysis.The results show that the time history and power spectral density curves of the bridge deck under the action of a single vehicle model generated by simulation are basically consistent with the actual test results,while the maximum value of the bridge deck acceleration time history under the action of the mixed traffic flow generated by simulation is slightly smaller than the measured data,and the main frequency distribution is relatively consistent.Due to only 4s data were collected when the acceleration time history was collected,the data of each model other than 4s were lost,resulting in a mediocre mixed acceleration time history effect generated by the simulation.(3)Collect the relevant design drawings of Liangang Bridge and Lirendong bridge,build the bridge model with ANSYS software.Referring to the relevant literature of vehicle model,the vehicle model was established at lane 1 and lane 2 respectively,and then the road roughness was generated by Matlab and input at the corresponding bridge nodes.Then,the random traffic flow in lane 1 and lane 2 generated in Chapter 2 is taken as load input to obtain the vibration response of the structure,and the calculation result is the relationship between displacement,velocity and acceleration and time within 20 minutes.Finally,by comparing the acceleration time history calculated by ANSYS with the measured value,the maximum dynamic displacement and maximum static displacement of the bridge structure calculated by ANSYS were extracted,and the impact coefficient was calculated and compared with the specification.The results show that the simulated acceleration time history of the bridge can well reflect the vibration response of the actual traffic flow on the bridge deck.The impact coefficients calculated by the specification are respectively 1.93 and1.59 times of the simulated values.