Preliminary Study On Seismic Fragility Analysis Method Of Bridge

The research on seismic fragility analysis of bridge structures can be traced back to more than 20 years ago.Although the research on seismic fragility analysis of bridge structures in China started relatively late,it also has more than ten years of research process.Reviving past studies,scholars have analyzed the seismic fragility of various Bridges and studied the uncertain factors of Bridges,which have obtained the rich research results and promoted the development of seismic theory of Bridges.However,in the existing researches,different methods of seismic fragility analysis are taken to analyze the seismic fragility of Bridges,and the conclusions are also different.So many problems need to be further studied.For example,the number of seismic waves to be selected,Which method is more suitable for seismic analysis in different situations,in the stage of building earthquake vulnerability model,which method is more appropriate to choose and what are the effects of different methods on the calculation results,etc.,are lack of sufficient study and discussion.Currently the seismic fragility analysis method of numerical analysis is most commonly used to obtain the seismic response of the structure by the incremental dynamic analysis method.However,the range and increment of the incremental dynamic analysis will affect the reliability of the results,and there is still a lack of further research in this field.Based on the above problems,herein studies the method which tooks the numerical analysis of seismic fragility analysis,mainly discusses the increment amplitude modulation range,increase of the dynamic analysis,seismic wave number,the establishment of the seismic fragility curve method and the calculation method of seismic requirements,etc.The main research contents of the thesis are as follows:1)Research on amplitude modulation range and increase amplitude of incremental dynamic method in seismic fragility analysis.Taking advantage of the feature that the maximum likelihood estimation method only needs structural damage information,a method using random sampling of the same distribution to study the number of ground motion records required for seismic fragility analysis is proposed.This method is taking to study the incremental dynamic range when the incremental dynamics is used to analyze the structural response and the maximum likelihood estimation method is used to establish the fragility curve.Later,the method is used to study the influence of the magnitude of the force increment on the fragility results.Finally,the range of incremental power and the suggested value of increase in fragility analysis are given.2)Research on the number of seismic waves required for different seismic fragility curve establishment methods.Based on the previously proposed quantitative research methods,by introducing the structural damage threshold and considering the uncertainty of each ground motion intensity,a sampling method suitable for both the maximum likelihood estimation method and the regression analysis method is proposed.Method,and got a lot of sample data.Then use maximum likelihood analysis method,linear regression,and nonlinear regression method to carry out statistical analysis on these data,and simulate the number of seismic waves by sampling times under each earthquake intensity.According to the estimation results under different sampling times,the recommended values of the number of seismic waves required under different accuracy requirements are obtained.In addition,through sampling with different dispersion distributions,the sensitivity of the calculation accuracy of the three fragility curve establishment methods to the dispersion of the sampled data is discussed.3)Research on calculation methods of structural seismic demandIn the current seismic design of bridges,the main methods for calculating structural requirements are time history analysis methods,response spectrum analysis methods,and power spectrum analysis methods.The seismic fragility analysis of structures mainly uses time-history analysis methods,and a few studies use response spectrum analysis methods.In this paper,a four-span continuous beam bridge is used as an example,and the time history analysis and response spectrum analysis methods are used to calculate the requirements,and the corresponding fragility curves are made to compare the differences between the two when they are applied to the seismic fragility analysis.And it is proposed that the power spectrum analysis method can be used for seismic fragility analysis.