Research On Temperature Influence Of Extradosed Cable-stayed Bridge Based On Modal Frequency

The structural performance of a bridge is affected by traffic load and ambient temperature during service stage,which leads to the decrease of its bearing capacity and even structural damage.Therefore,studying the temperature influence on the structural performance is of great significance to the bridge.At present,the research on temperature influence mostly focuses on static characteristics of various bridges and dynamic characteristics of medium-small span bridges,relatively less dynamic characteristics of long-span extradosed cable-stayed bridge.Based on the situation,this paper takes a prestressed concrete extradosed cable-stayed bridge with double-pylon and single-cable-plane,the structural system of which is cable-stayed rigid-frame cooperative system,as the supporting project,and conducts in-depth research on modifying the temperature influence on the dynamic characteristics and its application of a long-span extradosed cable-stayed bridge.Main works are as follows:(1)The health monitoring system of the extradosed cable-stayed bridge is briefly introduced,and the finite element software Midas/Civil is used to establish the model of the whole bridge,from which the emulational modal parameters are extracted through the analysis of dynamic characteristics.(2)The modal parameters of the bridge are identified according to the collected temperature and vibration acceleration signal data by health monitoring system.The degree of correlation between the identified modal parameters and temperature is analyzed,which turns out that temperature has different effects on three main modal parameters.Finally,the reason why temperature influence on the bridge's dynamic characteristics is approximately explained.(3)The principal component analysis(PCA)is applied to reduce the dimensionality of measured temperature data and the appropriate number of temperature principal components is extracted.Then,two methods are utilized to optimize the hyper-parameters which in turn are employed to build SVR models between temperature principal components and modal frequencies.The prediction performance of the models is tested and compared by some statistical indicators,and the temperature influence on modal frequencies is decreased prominently in the end.(4)Through numerical simulation of damage condition of different damage degree,the modal frequencies change value under temperature influence and structural damage are compared,and the identification effects of structural damage degree is compared by using the modal frequency before and after modifyng the temperature influence.Finally,based on the content of this chapter,the engineering significance is discussed.The results show that,i)temperature influence mainly affects the dynamic characteristics,especially the modal frequencies,of extradosed cable-stayed bridges by changing the elastic modulus of concrete materials,which shows a significant negative correlation between the modal frequencies and temperature,ii)it can be seen that the seasonal fluctuation of modal frequencies decreases distinctly through the comparison for the modal frequencies before and after temperature influence modification,and the standard deviation of the sample declines by about 75%,iii)the modal frequencies after modifying the temperature influence is used to identify the damage degree of the bridge,the accuracy of which is improved.The research results of the temperature influence on the dynamic characteristics and its application of long-span extradosed cable-stayed bridges with cable-stayed rigid-frame cooperative system can provide reference for the related research of similar bridges in the future.