Analysis On Earthquake Response Of Bridge Structures For Ground Fissure

Exploring the affects of grounds fissures to bridge structure earthquake responses is a difficult problem in reduce earthquake disaster research and engineering resistance designs field.Loess fissure ground is a species engineering sites,at present the research of the bridge structure earthquake responses in this loess sites is still the blank in domestic research.In view of this brand-new topic,this thesis on the basis of loess sites conditions with ground fissures of Xi'an areas,adopt intercross research methods to relate to multiple professional fields,have completed initial exploratory research,and have got some achievement.This thesis goal is to explore the difference of earthquake response for highway beam bridges structures,on the condition of loess ground fissures site considering near-seism, tele-seism and from under other conditions.The main contents as follows:(1) Tri-axis dynamic test and loess dynamical constitutive relation model confirmthis thesis discuss all kinds of constitutive relation models of clay soils,and obtain many test curves of loess clay soils samples by Tri-axis dynamic test.Hardin hyperbolic curve model is fit for description of loess clay and it can also be simplified to linear.(2) Loess soil layers prospect,dynamic characteristics test and building loess FEM modelsExploration soil layers distribution on a loess engineering site.And test the shear velocity of layers.Further more,building up the 2D layer FEM models,which can be used for loess sites for earthquake response analysis.(3) Prospect of vertical distribution of ground fissures in loess site and building models method of simulating loess fissuresTest vertical distribution of loess ground fissures in Xi'an by experiment method,after discussion the advantage and disadvantage in different advanced model building technique. Combining "live and death element" with "reduction parameter",have found a new way to simulate loess fissures in soil FEM model.(4) Completing the earthquake response analysis of loess clay site without fissuresInput the seismic waves excitations on the bottom of model by "Large mass method", complete time-stepping response analysis of loess site without fissures.Using several typical earthquake waves records with differential spectrum character,calculate earthquake response with different accelerated velocity levels on 0.1g,0.2g and 0.4g,to simulating the different condition of violent seism,minor seism,near seism and tele-seism.(5) Completing the earthquake response analysis of loess site with fissuresBuilding up the FEM soil models with fissures by the former skill.Using depth of fissures as variable,completing a series of time-stepping response analysis under different excitations with several typical earthquake waves records.The result indicate that there are complex relations in depth of fissures and excite spectrum.(6) Earthquake response analysis about reality bridges structuresAccording to standard design of concrete bridges structure,construct two models of reality beam bridge structure;completing a series of earthquake response analysis in bridge longitudinal direction,respectively input earthquake excitement on bottom of the bridge piers, through losses site,as well as through ground fissures.Through analysis reality bridges structures,the result indicate that the condition of loess fissures can affect the bridge earthquake responses in many respect.(7) Compile the program of data processing on basis of EMD principleOn basis of EMD(Empirical Mode Decomposition,EMD) principle,compile the program that can remove "drift component in displacement response",successfully complete data post treatment.The originality ideal and method of this thesis are:(1) In domestic,first put forward research the subject of bridge structure earthquake response in loess ground fissure site.Adopted multi-learning-fields and subjects intercross research methods,in linear elastic range,have completed initial exploratory research,and have got some research achievement.The research results indicate that loess ground fissure site has remarkable amendment response to earthquake drive waves.(2) From establishment loess site soil models and loess stress-strain constitutive relation to selection the input way manner of earthquake excitation waved,confirmation the dynamical calculate method,compile program of APDL,and post data processing,tried to find out a set of complete technical route for research work and the advanced technology integrated method.(3) Combine the EMD method with Large-Mass-Method of the input earthquake exciting, found one new way to effectively eliminate "the displacement drift" in the earthquake time-stepping methods.