Study On Ductility Seismic Design Of Railway Bridge

The basic principle of seismic design for bridges is to ensure the bridges safety underthe design earthquake. According to this principle,the seismic structure,which is designedaccording to the concept of ductility,must have a certain reliability to ensure the ductilityreserve under the expected design earthquake. In other words,we must in the sense ofprobability ensure that the ductility of structure exceeds the largest ductility demand underthe expected design earthquake. Therefore,when we design ductility structure,the ductilitydemand and ductility ability of structure must be analyzed and compared. The calculation ofductility can be obtained by nonlinear seismic response analysis,but this method is not easyfor researchs and designers to seismic designe. Therefore,studying how to simplify thecalculation process of seismic design has a important significance. Focused on the analysismethod for displacement ductility demand of structures and design method for ductilitystructures,this paper involves the following works:(1)The concept and basic principle and significance of ductility design is outlined;finally,the calculation of ductility demand and the research and existed problem of ductilitydemand spectra is discussed.( 2 ) The selection of elastic-plastic mechanical model,restoring model and theestablishment of bending moment-curvature relationship curve are discussed;the analysismethod of plastic response for piers using Midas/Civil finite element program is described;finally,an example is presented to verify the reliability of the procedure's calculated results.(3)The selection and classification of the ground motion records and the adjustmentmethod of peak acceleration are discussed;a lot of ground motion recorders are collected andgrouped according to the site classification;nonlinear time history analysis for single piersystem is carried out,then the corresponding ductility demand is calculated;based on theanalysis results,the relation curve between the ductility demand and the natural period isestablished,then the basic characteristics of ductility demand curve is discussed;finally theeffects of the structural parameters,site classification and other factors on the ductilitydemand curve are investigated.(4)In each group earthquake,the nonlinear time history analysis for single pier modelwith different vibration period is carried out,then the relationship between the displacementductility coefficient and linear-moment-ratio is investigated,and a functional relationshipbetween the two is established by statistical regressing of the analysis results. (5)At present,the single pier is used to overwhelming majority of railway bridge,considering the practical and operational of design,on the basis of seismic design codesabout ductile design method for bridge piers,a method of ductile seismic design is proposedfor conventional railway bridges.