Long-span Concrete-filled Steel Tube Arch Bridge Considering Scouring Earthquake Vulnerability Assessment

With the increasing maturity of construction technology and the increasing trend of bridge spans,concrete-filled steel tube arch bridges have many advantages and are widely used in engineering.In fact,the safety of the concrete-filled steel tube arch bridge during its service is affected by many factors.Among them,the scouring effect of the water flow has a greater impact on the concrete-filled steel tube arch bridge.The scouring makes part of the pile foundation of the bridge exposed and loses the horizontal restraint force due to the horizontal thrust of the arch ribs.Resulting in relative displacement at the arch foot more easily.On the other hand,earthquakes also bring huge challenges to the safety of concrete-filled steel tube arch bridges.When an earthquake occurs,huge energy is released,which has a serious impact on the bridge structure.In addition,the bridge plays an irreplaceable role in post-disaster reconstruction.Most areas of our country are located in the seismic zone,and some of the sea-crossing bridges built in the earthquake zone are suffering from the dual hazards of earthquakes and erosion.How to scientifically and effectively evaluate the effects of earthquakes and erosion has become a hot topic in the field of bridges.Choosing an appropriate damage assessment method is very important to the accuracy of the data.The traditional bridge damage assessment method only uses a few seismic waves for calculation,and cannot fully consider the uncertainty of ground motion,which brings inconvenience to obtaining accurate results.The seismic vulnerability method is proposed to fully consider the uncertainty of ground motions,and directly and effectively gives the damage probability of bridges under the action of earthquakes of different intensities,and is widely used by scholars at home and abroad.Based on the above,this paper,guided by the performance-based seismic design principles,uses the seismic vulnerability assessment method of bridge components to study the impact of scour on the vulnerability of Feiyan-type steel tube concrete arch bridge under earthquake.The specific research content is as follows:(1)Taking a large-span flying swallow-type concrete-filled steel tube arch bridge as the research background,elaborate the research background and significance of the subject,and analyze the current research status of domestic and foreign scholars on earthquake,erosion and bridge vulnerability.(2)Using Midas/Civil finite element analysis software,considering the material nonlinearity,the fiber section is used to establish the dynamic finite element model of the concrete-filled steel tube arch bridge,and the dynamic characteristics of the model are analyzed.(3)The internal force and displacement of the bridge are analyzed by nonlinear time history analysis method,and the maximum response and time history displacement of the components under earthquake action are obtained,and the seismic weak position of each component of the bridge is determined.(4)Explain the selection principle of the ground motion intensity index,and select 50 appropriate seismic waves according to the principle.The theory and analysis process of the seismic vulnerability of bridge components are introduced in detail,and the damage of each component of the bridge is determined by referring to previous domestic and foreign studies.Indicators and quantify them.On this basis,the vulnerability curve of each member of the arch bridge under the action of its own weight and earthquake is established and analyzed.(5)The type and mechanism of scouring are introduced in detail,and the advantages and disadvantages of the calculation formula of the scouring depth of the Chinese and American bridge specifications are compared.The maximum scouring depth of the bridge is calculated using the American standard formula HEC-18 scouring depth calculation theory,and the scouring depth is determined to be considered.After the component probability seismic demand model,and establish the fragility curve,analyze the impact of erosion on the fragility of the concrete-filled steel tube arch bridge component.Through the above research,the regular changes of the seismic performance of the concrete-filled steel tube arch bridge are revealed under the action of scouring,which provides a reference for the seismic performance evaluation of the concrete-filled steel tube arch bridge.