Study On The Influence Of Ground Motion Input On Structural Collapse Fragility

Since the 1990s,the Pacific Earthquake Engineering Research Center of the United States proposed four specific research frameworks for the next generation of performance-based earthquake engineering and seismic design,such as seismic hazard,structural response,structural fragility and loss assessment.In the process of ground motion selection in collapsed fragility and loss assessment in China,strong motion records are selected according to magnitude-epicenter distance,or according to the limitation conditions recommended by the American Applied Technology Council?ATC? research report,or directly using the records recommended by ATC63.According to controlling some seismic parameters,the number of selection ground motion records is quite large,and the risk level has not been reflected,and the subsequent collapsed fragility and loss calculation results can't truly reflect the seismic hazard level of the local site.Considering the seismic hazard and the characteristics of Chinese buildings,the traditional collapsed fragility analysis method will be improved by single-direction ground motion selection and bi-direction ground motion selection.The improved method is helpful for the seismic and risk assessment of the structure designed according to the current codes.The main contents of this paper are as follows:?1?The influence of seismic parameters such as magnitude,epicentral distance and site condition on collapse fragility is analyzed.The strong motion records from PEER database are divided into groups by constraining the range of one single variable,which is one of the earthquake magnitude,distance and site parameters(M,R,V_S30).The IDA method is used to analyze the collapse fragilities of three concrete frame structures,which are 3-floors,8-floors and 15-floors with different natural periods,respectively,and compared with ATC63 conditions.The results show that it is necessary to consider the influence of magnitude,epicentral distance and site condition when selecting earthquake motion input in structural collapse fragility analysis.At the same time,the shortcomings of three common methods for selecting ground motion are explained.The parameters I_Sa to measure the difference of relative energy of ground motion are proposed,which can well reflect the internal causes of the influence of seismic parameters,such as earthquake magnitude,epicentral distance and site conditions.?2?A method of structural collapse fragility analysis based on conditional mean spectrum?CMS?and IDA is proposed.Three different 2D structures are taken as an example and two seismic safety assessment projects in North China and Southwest China are selected as the research objects.Based on the improved IDA method,the fragility results obtained from uniform hazard spectrum,the code spectrum and recommended recordings in ATC63 data are discussed and analyzed.For the structure with a long period,the envelope CMS spectrum is proposed to consider the influence of multi-mode.Otherwise,the single-point periodic CMS spectrum causes the collapse fragility results to be significantly underestimated,which easily leads to the partial dangerous performance analysis results.?3?CMS is introduced to improve the selection process of seismic input in probabilistic risk analysis of structural demand based on traditional IDA method and the strip method.At the same time,the calculation process of structural collapse fragility analysis based on CMS and strip method is constructed.Firstly,the traditional full-period ground motion selection method is improved,which can effectively control the discreteness of ground motion,and the mean value is closer to the estimated value.Secondly,Based on the demand fragility,the traditional IDA and strip method are improved based on CMS,and compared with the traditional two nephogram methods.The fragility results of CMS-strip method and CMS-IDA method are in good agreement at four behavioral levels,while the final results of two nephogram methods are different because of the discreteness of wave selection.Finally,Based on the collapse fragility,the strip method based on conditional mean spectrum is introduced into the structural collapse fragility analysis.The rationality of the improved method is verified by comparing with CMS-IDA method,and the difference between CMS-IDA method and CMS-strip method is not significant under the rare annual exceedance probability level.?4?A method for selecting horizontal orthogonal and bidirectional ground motions is proposed,and a three-dimensional collapse fragility analysis and calculation process based on CMS is established,which is applied to the analysis of structural fragility surface.Firstly,the method of establishing a new database by rotating interval angle can effectively expand the alternative database and satisfy ground motion selection in engineering.Secondly,On the basis of single-direction ground motion selection method,the horizontal orthogonal bi-direction ground motion selection method is proposed.Compared with other tradition bi-direction ground motion selection methods such as the code,it is shown that the process has the advantages of considering the azimuth dependence of strong motion observation and the characteristics of natural horizontal bi-direction ground motion.Thirdly,it is to link the bi-direction ground motion selection,seismic risk and collapse fragility reasonably and scientifically,based on the concrete frame structure and the core tube structure.Thirdly,it is to link the bi-direction ground motion selection,seismic risk and collapse fragility reasonably and scientifically,based on the concrete frame structure and the core tube structure.Finally,the collapse fragility surface analysis method is constructed by means of conditional mean spectrum,bi-direction ground motion selection method,multi-angle input and vulnerability.Taking different frame structures as examples,the necessity of considering the direction of seismic input and the scientific rationality of vulnerability surface analysis are illustrated.