Research On The Mechanism Of Temperature Influencing Frequency Of Through Arch Bridge

In operation,the bridge is always affected by environmental factors such as traffic,wind,and temperature.Under long-term effects,the structure will change,which may cause significant loss of personnel and property.The method of identifying damage by modal frequency has become an important means of structural health monitoring.The complexity of the structure of the through arch bridge will lead to the complication of the dynamic characteristics,and the temperature effect will cause the uncertainty of the monitoring data under operating conditions,so that the identification indicators extracted by the data collected by the health monitoring system are not sensitive to changes in structural performance and the state of the structural health cannot be accurately identified.In order to separate the influence of ambient temperature,to accurately identify the dynamic characteristics of the through arch bridge,it is of great significance to study the mechanism of temperature influence on the through arch bridge's frequency.By using the equivalent multi-span elastic supported beam theoretical model,the formula of the arch and deck.The relation between the frequency and the shape,elastic modulus,boundary conditions and internal force of the bridge caused by temperature changes.Based on monitoring data such as acceleration,strain,displacement and temperature,the formation mechanism of modal frequency and temperature of Dashahe Bridge under the coupling of changing elastic modulus,boundary conditions,and internal forces is analyzed.Appling the daytime temperature and annual temperature based on the monitoring data to the ANSYS finite element model of Dashahe Bridge,the influence of each influence mode on the modal frequence of Dashahe Bridge is quantified,and the mechanism of the influence by the temperature on the Dashahe Bridge is obtained by comparing with the measured frequency changes.For an arch bridge that has been continuously monitored for 5 years,a genetic algorithm based BP neural network method is used to establish the temperature and arch bridge frequency correlation mode to remove the temperature's effect,and novelty index(NI)is proposed as a bridge structure performance identification index.By comparing the results of multiple linear regression and BP neural network,the feasibility and effectiveness of BP netwaok romoving the temperature influence on the frequency of arch bridge are verified.The study found that temperature changes the elastic modulus so that each order mode of the through arch bridge exhibits an annual negative correlation with temperature,and each order mode has a different sensitivity to elastic modulus changes caused by temperature.The temperature has little effect on the modal frequency of the through arch bridge by changing the hanger stiffness,the shape of the bridge,and the internal force of the bridge.The change of the bearing contact area has a great influence on the modal frequency of deck mode.The frequency of arch is negatively correlated with temperature due to the change of elastic modulus.The arch of the deck causes the contact area between the beam and the support to increase,which causes the frequency of deck increasing,leading to a positive correlation between the frequency and temperature of the deck.It is feasible and effective to use BP neural network method based on genetic algorithm optimization to remove the temperature's effect of arch bridge frequency and extract the bridge performance identification index to evaluate the bridge performance.