Seismic Analysis Of Continuous Girder Curved Bridge Considering Impact Behavior Under Near-or-Far Field Earthquake Ground Motions

With the development of society,the demand of curved bridge increases rapidly,especially in the field of urban overpass,expressway interchange constructions.Surmounting the obstacle of the restrains of the terrain,the bridge plays an important role in public transportation system.After a devastating earthquake,the trafficability of curved bridge will determine the progress and the efficiency of rescue operations.It is necessary for bridges to develop a well seismic design method.The curved bridges are widely applied,therefore more and more curved bridges are constructed in seismic area.Generally,there are some seismic phenomenon in the area which is near to the epicenter,for example containing velocity pulses which will cause a serious damage of constructions.Due to the geometrical irregularity,the curved bridges will emerge complicated internal forces under applied loads,which will contribute to a greater vulnerability of curved bridge itself.Therefore,it is important to study the variance of damage of curved bridges under near and far field earthquake.The results will be a useful reference to improve the corresponding design.In this thesis,a curved viaduct would be analyzed by loading near-field and far-field earthquake motions.The resulting respond shows the variances indeed exist.Main contents can be summarized as thus:(1)Due to the complexity of seismic respond of curved bridge,the impact often occurs between the adjacent girders.Thus it is necessary to apply an appropriate method to simulate the impact behavior.There are two approaches are commonly used in simulating the impact of bridges,which are the master-slave surface method infinite element mechanics and contact element method.Applying above tow method into a straight viaduct and a curved viaduct for seismic analysis.The resulting respond in the former shows more similarity and huge discrepancy in the later,for example,disparities occurring in impact force and accumulated impulse between two methods.Considering the impact feature of curved bridges,this study will choose master-slave surface method to simulate the impact behavior.(2)This thesis would take the fault distance as the criterion of near-filed earthquake and apply to filter eligible earthquake motions form 5.12 Wenchuan earthquake motions.Then use the Empirical Mode Decomposition(EMD)method to determine whether the velocity impulse exists in selected earthquake motions or not,then 3 near-field earthquake motions are selected.Eliminating the undersized Seismicrecords,3 far-field motions are selected.(3)Summarizing the seismic damage phenomenon of curved bridge,considering the post-quake trafficability,3 classifications of damage are suggested.Then specified criterion like the residual displacement,bearing strain,impact force,plastic strain of pier,and possibility of deck unseating is selected and quantitated.(4)Based on ABAQUS,applying the master-slave surface method for impact behavior,an finite element analysis model of a curved bridge which is origin from Lipan express is established.Input amplitude modulated earthquake records into the analysis model.The resulting seismic respond shows that the longitudinal displacement of superstructure of viaduct is greater that the radial.The collision occurs in the flange of main girder at the middle expansion joint of viaducts and in the bottom plate at side expansion joint.The impact force is greater in side expansion joint but the number of collisions is less.However,the impact force is smaller in middle expansion joint but the number of collisions is more.(5)Through a comprehensive comparison and analysis of above seismic respond,curved viaduct shows a greater damage in near-field earthquake.The responding data reveal higher possibility of deck unseating,bigger impact forces,greater damage stress and residual displacement of expanding joints etc.