| Earthquakes often occur in sequence,and aftershocks are usually accompanied by aftershocks.Statistics show that the incidence of strong aftershocks is as high as 89%,and in a few cases even with group earthquakes.However,the current seismic design codes and rules for highway bridges in China have not considered the impact of aftershocks.Therefore,this paper studies the anti-aftershock performance of reinforced concrete bridge structures,and obtains the anti-aftershock capability of existing reinforced concrete structures,which provides some references for bridge reinforcement in old bridges and multi-seismic areas.Considering the randomness of the earthquake,the damage condition of the structure under seismic loading is usually described by the probability of overshoot.In this paper,XTRACT software is used to analyze the equivalent yield curvature,ultimate curvature,equivalent yield bending moment and other parameters of the bottom section of the pier and transform it into the parameters required for the damage index.The nonlinear seismic analysis software OpenSEES was used to analyze the structural response of reinforced concrete piers with different axial compression ratios,reinforcement ratios,slenderness ratios and diameters,and reinforced concrete continuous girder bridges under the action of 200 main aftershocks;The vulnerability of reinforced concrete piers and reinforced concrete bridges under the action of main shock and main aftershocks was studied.The main research contents are as follows:(1)This paper collects the common seismic damages of bridges caused by aftershocks in major earthquakes at home and abroad,and summarizes the research background and research status of the seismic response characteristics of bridges and the vulnerability of bridge structures.(2)The advantages and disadvantages of the main aftershock seismic wave synthesis method and the vulnerability curve are compared.The structural overshoot probability formula with the response spectrum acceleration as the seismic intensity index is derived.The damage criterion and damage index of different structures are compared.Combined with the research content,the damage index of seismic vulnerability analysis is determined.(3)According to the existing pier and column tests on PEER website,the numerical model of pier and column is established by using OpenSEES software,and the quasi-static analysis of the numerical model is carried out,and the mechanical properties of numerical simulation of pier and column are extracted and compared with the test results to verify the reliability of the modeling method.(4)According to the division of site soil by USGS method in the United States,the long holding time seismic wave in PEER database is selected to screen the main shock and aftershock seismic wave in accordance with B,class C site and aftershock respectively.The nonlinear time history analysis of reinforced concrete pier columns in engineering is carried out,the logarithmic scattered point diagram of damage index and spectral acceleration(Sa)is drawn,the scattered point diagram is fitted linearly,and the probability of pier column surpassing different damage states is obtained.The effects of axial compression ratio,reinforcement ratio,slenderness ratio and pier column diameter on the vulnerability of pier columns were studied.(5)Based on a practical project,the finite element model of continuous beam bridge is established by OpenSEES software.The time history analysis of single bidirectional main shock and main aftershock in class C site of continuous beam bridge is carried out,and the probability of surpassing different damage states of fixed pier,fixed bearing and sliding bearing in continuous beam bridge under the action of unidirectional and bidirectional main aftershock is studied.Comparison of the vulnerability of each component of continuous beam bridge and the maximum increment of transcendence probability caused by aftershocks at different sites. |
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