Research On Influence Of Temperature And Vehicle Load On Modal Frequency Of Bridge

In actual operation,the modal frequency of the bridge is often changed by environmental factors such as temperature and vehicle load.This change will confuse or even cover up the frequency change caused by structural damage,which will cause great problems to the assessment of the health status of the bridge.In this paper,based on a large number of measured temperature and acceleration data,the correlation study of temperature,vehicle load and frequency is carried out,with a view to revealing the influence of temperature and vehicle load on frequency.The main research contents and conclusions are as follows:(1)The reason why temperature affects frequency.The Midas Civil software was used to establish the finite element model of the Hedong Bridge,and the frequency change values caused by the temperature-induced elastic modulus,initial internal force and support stiffness change were calculated respectively.Comparing the calculation results,it is found that the change in elastic modulus and the stiffness of the support due to temperature are the main reasons for the frequency change.When the support freezes,the effect on the frequency is greater,and the initial internal force change caused by temperature affects the frequency It's very small and can basically be ignored.(2)Correlation analysis of frequency and temperature.Based on the monitoring data of about 10 months,the frequency and temperature correlation analysis is carried out,and the monitoring data is divided into four time intervals of 10 min,20min,30 min and 1h.The peak picking method is used to obtain the first four-order vertical bending frequency value of each period.The average value of the temperature value measured by the full-bridge temperaturesensor in each period is used as the temperature representative,and the root mean square of acceleration(ARMS)of each period is used as the period representative value of vehicle load.The number of vertical bending frequency samples,temperature samples and ARMS samples obtained at the same time interval are the same,corresponding to each other according to the time axis.The number of sample groups obtained in the four time intervals are 27504,13752,9168 and 4584,respectively.In order to remove the influence of vehicle load,the frequency and temperature samples when the ARMS value is [0.0070,0.0072] are selected for correlation analysis.The analysis found that the frequency is negatively correlated with temperature,of which the third-order vertical bending frequency has the largest correlation and the second-order vertical bending frequency has the smallest correlation.As the analysis time interval increases,the dispersion degree of vertical bending frequency of each order decreases,and the negative correlation with temperature increases at the same time.After excluding the influence of vehicle load,the correlation between frequency and temperature is more obvious.(3)Correlation analysis of frequency and vehicle load.Based on the above measured data,the correlation between frequency and vehicle load is analyzed.From the above analysis,it is learned that the analysis time interval should not be too small.Therefore,only 30 min and1h time interval analysis are used in the correlation study between frequency and vehicle load.In order to remove the influence of temperature,through statistical analysis of the temperature data,the frequency and ARMS samples with the temperature value of [21,22]were selected for correlation analysis.After analysis,it is found that the frequency is negatively correlated with the vehicle load,and the correlation between the vertical bending frequency of each order and the vehicle load is relatively strong,of which the fourth-order vertical bending frequency has the largest correlation and the third-order vertical bending frequency has the smallest correlation.In the two analysis time intervals,as the analysis time interval increases,the degree of dispersion of the vertical bending frequency of each order decreases,and the negative correlation with the vehicle load increases at the same time.