Study On Dynamic Characteristics Of Train-Long Span Cable-Stayed Bridge System Under Inconsistent Seismic Excitation

With the rapid development of urban rail transit worldwide,the scale of rail transit construction in China is also expanding.Long span bridges are often used as hub projects for transportation and play a crucial role.As one of the classic types of long span cable-stayed bridges,cable-stayed bridges are also developing rapidly.However,earthquakes frequently occur in southwest China,and earthquake disasters inevitably cause changes in the dynamic characteristics of bridges.Rail trains running on bridges are inevitably affected by them,affecting people’s riding experience,and even endangering the safety of people’s lives and property.However,the dynamic problem of the train bridge system under seismic excitation is not a simple system superposition problem,so the research on the dynamic characteristics of the train long span cable-stayed bridge system under non-uniform seismic excitation becomes particularly important.Taking the Dongshuimen Yangtze River Bridge as the engineering background,this thesis establishes a coupled dynamic model of train long span cable-stayed bridge,conducts response spectrum analysis and time-history analysis considering traveling wave effects on the model,and explores the impact of non-uniform seismic excitation on the dynamic characteristics of the train long span cable-stayed bridge system.The main research contents of this article include:Firstly,the development of domestic rail transit and cable-stayed bridges is reviewed,focusing on the structural characteristics of cable-stayed bridges,and earthquake disasters are also described.The research status of vehicle bridge system dynamics and the impact of earthquake action on vehicle bridge systems at home and abroad is summarized,leading to the research topic of this article.Then,the basic theory and characteristics of seismic response analysis are briefly introduced.Based on the theory of train track bridge dynamic interaction,the vehicle subsystem model,track subsystem model,and bridge beam subsystem model are used to achieve vehicle bridge coupling using wheel rail and bridge rail relationships.At the same time,considering the impact of seismic excitation,a dynamic model of the train long span cable-stayed bridge coupling system under seismic excitation is established,According to the specifications,the US level 5 spectral irregularity is selected as the initial excitation of the system.Secondly,based on the bridge design data,a long-span cable-stayed bridge model is established based on the finite element method.By comparing the modal analysis of the bridge finite element model with the on-site bridge pulsation test results,it is verified that the bridge model meets the calculation requirements and has high accuracy.By analyzing the basic dynamic characteristics of the bridge,it can be found that the first mode of vibration of the entire bridge is a positive symmetric vertical bending of the main beam,with a fundamental frequency of 0.313Hz and dense modes.The CQC mode combination method should be used for response spectrum analysis.The selection principle of the reaction spectrum was also introduced in detail,and the research conditions were determined.Finally,based on the above model,a seismic response spectrum analysis and a time history analysis considering traveling wave effects are conducted.By comparing the vehicle bridge dynamic response results from response spectrum analysis and time history analysis,the impact of non-uniform seismic excitation on the dynamic characteristics of the train long span cable-stayed bridge system is explored.The comparison of response spectrum analysis and time history analysis results shows that the maximum vertical displacement at 1/2 of the midspan of the bridge with a large midspan is 40.86mm.In response spectrum analysis,the maximum vertical displacement and lateral displacement of each key point of the bridge tower are 56.52 mm and 4.02 mm respectively at the vertex A of the bridge tower.The maximum vertical and lateral accelerations at each key point of the bridge tower are 0.057m/s~2 and 0.112m/s~2 respectively at the top point A of the bridge tower.In the time history analysis,the maximum vertical displacement obtained at the top point A of the bridge tower is 57.47mm,and the maximum lateral displacement obtained is 4.16mm.In the time history analysis,the maximum vertical and lateral accelerations at each key point of the bridge tower are 0.059m/s~2 and 0.112m/s~2respectively at the top point A of the bridge tower.Finally,it is concluded that the time history analysis and response spectrum analysis considering non-uniform seismic excitation have no absolute impact on the calculated results of the dynamic characteristics of the vehicle bridge system,and the specific impact depends on the dynamic characteristics indicators analyzed.