Dynamic Response And Geometric Nonlincarity Analysis Of High-pier Under Strong Earthquake

The research of bridge stability under strong earthquake is always the hot issue inthe field of seismic engineering. With the implementation of the strategy of the westerncountry,high-pier bridge with its unique performance,across steep mountains and gullyregion of loess plateau,always plays lifeline of the inside and outside unicom.Thereforeit has very important practical significance to do more high pier bridge seismicbehavior research. Pier will also play an important role as the substructure. In thispaper, the National Natural Science Fund Project "based on the theory of multi-hazarddisaster chain to explore the evolution of the law（50879097）" based on seismicanalysis of high pier bridge research using.<Guidelines for Seismic Design of HigwayBridges>（JTG/TB02-02-2008）clearly defines that ordinary bridge is the pier highbelow30m.The design and analysis of ordinary bridge can still follow a large numberof cumulative earthquake disaster experience and theoretical research.The bridge ofpier high above30m is unordinary bridge of complicated dynamic response,whichmust separate analysis.But our western bridges construction is generally more than60m,therefore high-pier bridges must separate design and analysis.A finite elementmodel has been established to analyze continuous rigid frame bridges with highpiers,which has pounding bottom consolidation and constrained beam.Workingconditions of linear elasticity and geometrically nonlinear based,importing transverseexcitation,vertical excitation,transverse and vertical two-dimensional excitations,theidea that high pier focalization should be designed consideration and mainly revealsresponse pattern under strong earthquake and failure mechanism,getting themechanical characteristic by chain-cutting disaster mitigation from gestation sourcemajorization for pier.The main research contents and achievements of this paper are asfollows.1.The author analyzed the current situation and the developing trend of thedynamic response of high pier and pier stability under earthquake.According nonlineartheory, seismic excitation is supplyed to78meters high hollow RC pier and analysispier’s forces and displacements in gravity second-order effect.Having consideringgravity second-order effects,the dynamic response of high pier is enhanced.2.Through interception continuous rigid frame bridge with high piers modelantimere and applying symmetry constraint on cross section, respectively import transverse excitation,vertical excitation,transverse and vertical two-dimensionalexcitation based on working conditions of linear elasticity and geometricallynonlinear.Considering six working conditions comparative analysis, the results verifiedthat displacement values and internal force values of cross sections increased about5%considering large deformation effect which could be more close to real force situationon pier.3.The internal force values of core area in middle pier was relatively small,butcompared to other area the deformation was large.Visibly equivalent part ofdeformation can meet the coordination on pier deformation.Therefore it is important toincrease flexibility,arrange reinforcement flexibly and decrease its weight.Soflexible-pier should be optimal selection.4.Compared with three excitations, vertical excitation provided less contribution totransverse and longitudinal displacements than other excitations.It is connected closelywith fixed constraint in the pier bottom.In the basic part of bridge pier,strengtheningpile-soil integrity could decreased contribution ratio of vertical excitation.5.In three kinds of excitations,the trend in longitudinal displacement is differentfrom transverse displacement.Transverse displacement gradually increased along thepier, longitudinal displacement of forward direction got maximal value over the middleof pier and longitudinal displacement of negative direction got maximal value at thelower part of pier. It is connected with rigidness of longitudinal and transversedirection.The core area in pier bottom had high force and low deformation,would occurplastic hinge at first.Then the superstructure effected on core area in pier top,appearingplastic hinge secondly.At last,external force gradually concentrated to the central pierand constrained deformation.The third plastic hinge would appear in the central pier.