The Research On Earthquake-reduction And Seismic-isolation Measures To Extradosed Cable-stayed Bridge Of High Speed Rail

In recent years, our rapid economic growth offers a chance for the traffic cause todevelop vigorously. The form of bridge structure changes quickly and especially the railwaybridge’s structure is no longer the simply supported beam. Various new type bridge structureshave make people look on them gradually. The low-pylon cable-stayed bridge, which is oneof the new type bridge structures, has obtained wide attention and application, while it isapplied to the railway bridge infrequently. Study on the measures for seismic and seismicmitigation and isolation is in primary stage. The railway is lifeline engineering when thedangers happen, so the seismic for the railway bridge is more important. Therefore, study onseismic and seismic mitigation and isolation of the railway bridge is the important content ofstructural dynamic safety study all the time. Study on the measures for seismic and seismicmitigation and isolation in the railway bridge field can provide references for the same typebridge. It has important significance.This paper sees the high extradosed cable-stayed bridge as engineering background. Thefinite element software Midas is used to build the full-bridge finite element model to analyzethe structural basic dynamic characteristics and earthquake response. Combined with theseismic requirement of railway, the seismic mitigation and isolation is designed in this paper.In addition, the seismic mitigation and isolation is analyzed and evaluated. The main jobs andconclusions are as flows:(1) Consul relative references, understand the study and the application present situationof bridge’s seismic mitigation and isolation, master the definition and structural characteristicsof the extradosed cable-stayed bridge, be familiar to the development and the study presentsituation of the extradosed cable-stayed bridge. These jobs can provide method basis to studythe seismic mitigation and isolation measures of low-pylon cable-stayed bridge.(2) Use general finite element calculation software Midas to build the dynamic analysisfinite element model of the high speed rail extradosed cable-stayed bridge. Considering theeffect of rigid foundation and elastic foundation, the free vibration characteristic is studiedunder the comparison of above two conditions. Then, each model shape are extracted andanalyzed to prepare for analyzing the structural earthquake response.(3) Use the response spectrum method and the dynamic time-history analysis method,calculate the high speed rail extradosed cable-stayed bridge’s earthquake response, compareand analyze the calculation results, obtain the conclusion that the displacement of theresponse spectrum method is lager than that of the dynamic time-history analysis method. Atthe same time, the displacement and the internal force of key parts, which are combined withthe displacement characteristics under the condition of normal operation and earth quake, are obtained to provide the data support for the seismic mitigation and isolation design.(4) Based on the displacement limit method, the seismic mitigation and isolationmeasure is designed. The two kinds of seismic mitigation and isolation measures, which arelead-rubber bearing and viscoelastic energy dissipation device, are designed and optimizedrespectively. And then, the suitable parameters of lead-rubber bearing and viscoelastic energydissipation device are input into the finite element model and the dynamic time-historyanalysis of the displacement and internal force are undertaken. The conclusions, which are thedisplacement, the internal force and the bearing reflection under the earth quake, are obtainedbased on these two seismic mitigation and isolation measures. In addition, the bridgedisplacements under normal operation are checked and calculated.(5) Compared with the calculation results under no seismic mitigation and isolationmeasures, the dynamic time history calculation results are obtained after setting seismicmitigation and isolation bearings. Using these two kinds of bearings, the displacement andinternal force of the bridge’s fixed anchorage decreased significantly when earth quakehappened. Moreover, the fixed anchorage and the activities piers bear the force from the maingirder. So the internal force of the main girder decreases, while the displacement increasesbecause of the bearing deformation. And the maximum displacement is still within the railwaybridge requirement under the earthquake. It shows that the two kinds of seismic mitigationand isolation designs increase the bridge damp and prolong the natural vibration period undermeeting the requirement of the bridge normal operation. So it can protect the bridge when theearthquake happens.