| Since bridges are in the field for a long time,the structural performance of bridges is bound to be affected by various environments.Therefore,health monitoring systems were installed during the construction period of many bridges in order to monitor the operation of bridges in real time and use the monitoring data to make health assessment and maintenance decisions.However,the instability of external environmental effects can cause uncertainty in the variation of structural dynamic characteristic parameters.The first is that the ambient temperature has a long-term effect on the dynamic parameters of the bridge,so it is necessary to study the effect of temperature on the dynamic parameters of the bridge in order to assess the changes in the structural performance of the bridge itself.As the world’s largest span of rail-cum-road steel arch bridge,the Tianshenggang channel bridge is representative in terms of span and structural form.In addition,the main material of the bridge is steel,steel specific heat capacity is small,affected by the temperature is obvious,its temperature role can not be ignored.The following studies will be conducted for the Tianshenggang Channel Bridge:(1)Firstly,based on the design documents and combined with ANSYS software functions,a finite element model of the bridge was established and modal analysis was performed to derive the inherent dynamic characteristics parameters of the bridge itself.Then,the theoretical analysis shows that the temperature affects the modal frequency change of the bridge mainly by affecting the elastic modulus of the bridge,and the effect of the elastic modulus change,temperature stress and the joint action of both on the modal state of the bridge is considered in the bridge model.The results are consistent with the theoretical analysis when acting alone;the effect of low temperature on the modal frequency of the bridge is more significant when the two act together.(2)The theoretical derivation of the modal parameter identification algorithm based on CMIF theory was carried out,and the selection principles of the key parameters of the method were summarized,and the identification process of the modal parameters of the method was sorted out.The algorithm is optimized to achieve automatic identification of modal parameters and reduce the instability of identification results caused by human factors.The effectiveness and accuracy of the algorithm were subsequently verified using ANSYS simulation data.(3)Based on the measured data from the bridge monitoring system,the structural temperature distribution and acceleration response characteristics of the bridge were analyzed,proving that the measured data can effectively reflect the changes of the bridge’s operating condition.The first 3 orders of vertical vibration modal frequencies,damping ratios and 1st order modal vibration patterns of the bridge were identified using an automatic identification algorithm of modal parameters based on CMIF theory.(4)The measured data of 15 days in different seasons were used as research samples to find out the trend of modal parameters of the bridge,and the correlation analysis and linear regression analysis were performed between the modal parameters and the structure temperature to obtain the law of temperature influence on the dynamic characteristics of the bridge.In order to further find out the trend of the structural performance of the bridge itself,the regression model of the modal frequency of the bridge and the structural temperature was established using partial least squares regression(PLS),and the model was verified to have good regression capability.Based on the regression model,the influence of temperature on the modal frequency of the bridge is eliminated,exposing the modal frequency changes caused by changes in the bridge’s own performance,which can provide a decision basis and reference index for subsequent bridge health diagnosis,performance assessment and operation and maintenance. |
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