The Seismic Fragility Analysis Of Rc Frame Structure Taking Account Of Mainshock-aftershock Sequence Action

A large number of seismic historical data shows that a strong earthquake is always accompanied by a large number of aftershocks.According to the statistical data,the occurrence rate of strong aftershocks or relative strong aftershocks reached 89%.The strength index of this secondary energy release process with high probability of occurrence is not necessarily lower than that of the mainshock,while it is quite common that strength index of aftershock is higher than the mainshock strength index.After the main earthquake,buildings may have entered the nonlinear stage where the plastic deformation and stiffness degradation appeared as well as bearing capacity reduced.Therefore,when buildings undergo the subsequent aftershock sequence,even smaller energy release may multiply the risk of earthquake and causes serious consequences.However,most of the countries in the world,including China,there is no content of structural seismic design considering the effect of the mainshock-aftershock sequence in current seismic design code.Therefore,it is of great practical significance to analyze the dynamic response of the structure under the action of the mainshock-aftershock and to quantify the damage accumulation process.In this paper,the dynamic response of the RC frame structure under the action of the mainshock-aftershock sequence-type ground motion is studied.The main work includes the following aspects:(1)Review the research progress of mainshock-aftershock ground motion and its structural dynamic analysis at home and abroad,and introduce the background and significance of this research.(2)In accordance with the most detailed mainshock-aftershock seismic records by permanent stations in Wenchuan earthquake of China and refer to the NGA conditions for screening ground motion records,1158 mainshock-aftershock ground motion records of is statistical analysed.Classic characteristic analysis process of ground motion is introduced.The relationship between aftershocks occurrence rate and the time after the mainshock is given through the regression calculation.The attenuation relationship between aftershock PGA and magnitude and epicentral distance under different surface conditions in different directions is fitting calculated.(3)According to Chinese architectural design code,a 6 level 3 span RC frame structure is designed.The structural performance variable is taken as the damage indexand with which the limit values corresponding to different failure states of the index are given.The calculation method of the structural performance variables under the continuous action of aftershocks is introduced.(4)According to the seismic risk analysis results,the mainshock-aftershock ground motion records of Wenchuan earthquake recorded by the same station in the same direction is combined to "mainshock + single aftershock" and "mainshock + multiple aftershocks" records following the real time of occurrence.the vulnerability analysis of input RC frame structure.The vulnerability analysis is carried out by combining the combined records into the RC framework.In summary,this paper choose the analytical logic of seismic risk analysis,the first part is seismic hazard analysis which studies the characteristics of the mainshock-aftershock sequence-type ground motion;Then structural vulnerability analysis do calculate and analyze to the damage accumulation of the RC frame structure under the action of the mainshock-aftershock sequence-type ground motion.