Study On Seismic Response And Vulnerability Of Long-span Continuous Rigid Frame Bridges

In recent decades,especially in the 21 st century,with the needs of road traffic construction in China,bridge construction has entered a period of rapid development.Continuous rigid frame bridge has been rapidly applied and developed,and has become one of the main types of long-span bridges,because of its mature construction and design,better control of construction quality and time limit,simple maintenance and other construction characteristics.At the same time,it has the structural advantages of reasonable stress on main girder,full play of structural potential,span capacity and stress capacity of piers.However,in recent years,destructive earthquakes occur frequently at home and abroad.Bridges,as the most important part of the transportation system,once seriously damaged under the earthquake,will pose a great threat to people’s life and property safety.Therefore,it is necessary to study the vulnerability of continuous rigid frame bridges under ground motion,so as to provide a reference for the assessment of damage degree and scientific prevention of earthquake disasters in practical projects.Based on the background of a 170 m continuous rigid frame bridge,the main research contents are as follows:(1)This paper expounds the severity of natural disaster damage,the development and characteristics of continuous rigid frame bridge,and introduces the research status,development process and three commonly used seismic analysis methods of bridge structure vulnerability in detail.(2)Based on MIDAS CIVIL software,the finite element model of continuous rigid frame bridge is established,and the dynamic characteristics of the example bridge are analyzed,and the first ten natural vibration periods and modes of the bridge are obtained.The displacement and internal force responses of the bridge under the longitudinal and transverse ground motions are calculated by using the time history analysis method among the static method,response spectrum method and time history analysis method.(3)This paper introduces the analysis method of vulnerability theory and the procedure of getting vulnerability curve,sets up the plastic hinge on the basis of the existing finite element model,establishes the dynamic elastoplastic analysis model of theexample bridge,selects 15 seismic waves according to the requirements,analyzes the moment curvature of the pier,uses the curvature ductility ratio as the damage index to divide the different damage levels,and then based on the incremental dynamic component The seismic vulnerability curve of bridge pier and support along and across the bridge direction is obtained by using the spectral acceleration SA as the ground motion parameter.Finally,the vulnerability curve of three groups of different bridge pier heights is obtained by changing the height of the bridge pier,and the influence of the change of the height of the bridge pier on the seismic vulnerability of the bridge is studied.The results show that the probability of pier damage decreases with the increase of pier height under the earthquake along and across the bridge,and the probability of bearing damage increases with the increase of pier height.(4)Based on the theory of structural reliability,the seismic vulnerability of bridge system is calculated by the first-order limit estimation method on the basis of the vulnerability of two important structural components of bridge pier and support,and the influence of the height change of bridge pier on the seismic vulnerability of bridge system is analyzed.According to the seismic vulnerability of the bridge system,the traffic flow and traffic time are calculated by the relevant formula to evaluate the post earthquake traffic capacity of the bridge,and the influence of the change of pier height on the post earthquake traffic capacity is analyzed.In this paper,the seismic response of continuous rigid frame bridge,seismic vulnerability of components,seismic vulnerability of the whole bridge system,post earthquake traffic capacity and the influence of pier height change on seismic vulnerability and traffic capacity are studied and analyzed,which has certain reference value for the design and research of continuous rigid frame bridge in the future.