Study On The Improved IDA Method For Structural Seismic Fragility Analysis

Structural fragility analysis is the conditional probability of various failure states of the engineering structure under the action of different strength earthquake,which can quantitatively describe the seismic performance of the structure in the sense of probability.Incremental dynamic analysis(IDA)is a commonly used fragility analysis method,which adjusts the selected ground motion intensity according to certain rules,and takes a series of ground motion after manual amplitude modulation as the excitation input of the structure,so as to obtain the structure response.However,as for most of the current IDA methods,there are same defects such as too much calculation,time-consuming analysis and low efficiency.These problems seriously affect the development and application of fragility analysis based on IDA.It is more and more urgent to find improved methods to solve the related problems.Based on the fact that IDA method is a research method based on elastoplastic dynamic time history analysis,this paper considers two aspects to simplify the fragility analysis based on IDA method: on the one hand,it can reduce the total IDA time consumption by establishing a simplified model and reducing the time of single time history analysis;on the other hand,it can reduce IDA consumption by reducing the number of elastoplastic dynamic time history analysis.The specific research is as follows:(1)A simplified fragility analysis method based on the strength adaptive Bouc-Wen alternative model is proposed.In this chapter,we propose to use Bouc-Wen model hysteretic element instead of each floor structure to build a chain type multi degree of freedom system,and use it as a simplified alternative model of 5-story reinforced concrete frame structure.In addition,considering the different failure modes of the structure under different earthquake intensity,the simplified model established in this paper is a strength adaptive model,and its relevant parameters change with the change of strength parameter PGA.In order to determine the parameters of Bouc-Wen model,a two-stage parameter determination method based on the least square method is proposed.At last,the analysis efficiency and calculation accuracy of the simplified fragility analysis method and the traditional fragility analysis method are compared through the structural calculation example,which shows that the method can also guarantee the accuracy and improve the efficiency by ten times.(2)A simplified fragility analysis method based on a single artificial ground motion record is proposed.In this paper,the average response spectrum and logarithm average response spectrum of multiple seismic records in the basic IDA method are selected as the target response spectrum.Power spectrum and amplitude spectrum methods are used to modify the initial artificial ground motion records so that its response spectrum gradually approaches the target response spectrum.Then the fragility analysis based on IDA method is carried out by using the single artificial ground motion record.At last,the analysis efficiency and calculation accuracy of the simplified fragility analysis method and the traditional fragility analysis method are compared through the structural calculation example,which shows that the method can also guarantee the accuracy and improve the efficiency by ten times.