Fragility Analysis Of Steel Frame Structure Based On IDA Under Mainshock-aftershock Sequences

Seismic investigation has demonstrated that aftershocks often occur after the main earthquake in a certain distance scope,which will cause more severe damage to structure.Impact of aftershock for structure earthquake-resistance performance is not be considered in the current design provisions,which makes the structure design unsafe.In this paper,near-field pluse-like and far-field mainshock-aftershock sequences were chosen.The 8-story steel frame model was taken as the research object.Considering specific initial damage of structure under mainshock,the aftershock and mainshock-aftershock vulnerability of structure was analyzed,the main research contents as follows:（1）Choose the mainshock-aftershock sequences that were used for structure analyze.20 near-field pluse-like and 20 far-field mainshock-aftershock sequences were chosen from Chi-Chi earthquake in five aspects which include moment magnitude M_W,peak ground acceleration PGA,peak ground acceleration PGV,mean shear wave velocity and whether the record is pluse-like,and two kind of mainshock-aftershock sequences were compared by the standard response spectrum.（2）Conduct aftershock IDA analysis of mainshock damage steel structure.Suitability of the maximum transient story drift ratioθ_maxand the maximum residual story drift ratioθ_resas mainshock damage index measures through variability of aftershock IDAcurves;after the structure reached five damage states of undamaged and DS1～DS4 under the mainshock,aftershock IDA analysis was carried out to study the influence of damage scenarios of mainshock on IDA curves of aftershock.（3）Analyze the influence of ground motion intensity selection on aftershock IDA curves of steel structure.10 ground motion intensity measures were chosen,then suitability of them measures through variability and correlation are studied on aftershock IDA analysis.（4）The aftershock vulnerability analysis and mainshock-aftershock vulnerability analysis of steel frame structure were carried out.Using the experience accumulation function as the probability function model,the vulnerability curves of the mainshock and the aftershock vulnerability curves of the damaged structures at various performan-ce levels were obtained,and the effects of five damage states,DS1～DS4,on the aftershock seismic performance were analyzed.Based on formula of total probability,the vulnerability curves of the mainshock-aftershocks at various performa-nce levels under different intensity ratios of the mainshock-aftershocks were obtained,and the impact of the two types of ground motion on the collapse ability of the structure was compared through the Collapse Margin Ratio CMR...