Seismic Performance Evaluation Of Continuous Girder Bridge Under Sequence Earthquake

Under the action of aftershocks,the damage of bridge structure will be further developed on the basis of that caused by the main earthquake,resulting in more serious damage.In this paper,Tianshui County cross traffic relief project overpass as the engineering background,select two of them(a straight beam bridge,a curved beam bridge)as the research object,carry out the vulnerability analysis under the action of sequence earthquake,and compare with the vulnerability under the action of main earthquake,evaluate the seismic performance of the research object under the action of sequence earthquake.The main research contents include the following aspects(1)Through reading a large number of literature and data,this paper introduces in detail the research status of bridge earthquake resistance and sequence earthquake at home and abroad,summarizes the construction method of sequence earthquake,expounds the uniform design method and response surface method used in this paper,and introduces the vulnerability theory and damage index determination method.(2)Based on the actual project,considering the pile-soil interaction,the nonlinear finite element models of two research objects are established by using CSi Bridge finite element software.Because the pier is short,the shear spring is added at the bottom of the pier to simulate the possible shear failure;the Maxwell mechanical model is used to simulate the lock up device,and the SIMPLE and Mander constitutive relation curve are used to modeling reinforcement and concrete respectively for nonlinear analysis of RC pier.The natural vibration characteristics of the whole bridge are analyzed.(3)According to the site classification of the bridge site,a series of seismic records are selected from the American peer seismic database as the main earthquake,and the one with the largest magnitude is selected as the aftershock in the corresponding aftershock records.Given a certain time interval between the aftershock and the main earthquake,the tectonic sequence of seismicity is obtained.(4)According to the uniform design table,the sample pairs of "bridge main earthquake" and "bridge sequence earthquake" are established.(5)The moment curvature analysis of the bridge pier section is carried out.The displacement ductility ratio is selected as the damage index of the bridge pier,and the shear strain is taken as the damage index of the bearing.The damage index under different damage states is defined.Based on the sample data,the response surface function fitting is carried out to calculate the response of the bridge structure under the seismic action of each strength.Through the logarithmic regression analysis,the component vulnerability curve is drawn Based on the first-order boundary estimation method,the system vulnerability curve is established.(6)The results show that the response of each component increases in varying degrees under the action of sequence earthquake,and the residual displacement of pier top under the action of main earthquake will further develop after the action of aftershock.(7)The vulnerability of components and system under the action of main earthquake and sequence earthquake is compared,and the quantitative analysis is carried out.It is found that the vulnerability under the action of sequence earthquake is greater than that under the action of main earthquake at both component level and system level,which provides reference for the future seismic design work and the development of specifications of bridges.