| A major earthquake is followed by a lot of aftershocks.Under the action of the mainshock-aftershock sequences,the aftershock can cause additional damage to the damaged structure by the mainshock,or even cause it to collapse,especially for the low ductility structure.The seismic design codes in China and other countries' only consider one earthquake and do not consider the influence of the mainshock-aftershock sequences on the structure.In China,there are a large number of old existing lowductile reinforced concrete(RC)structures,which have not been subjected to seismic design,insufficient level of seismic design or lack of seismic structural measures,and have been in service for many years.These structures have become weak for seismic fortification of urban building structures.The low-ductile structure damaged by the major earthquake will increase the probability of serious damage when it experiences the aftershock again.However,the existing research on the seismic performance of this kind of low-ductile structure under the action of the mainshock-aftershock sequences is not clear enough.Based on the existing research,this paper further studies the seismic performance evaluation of low-ductile structures under the action of the mainshock-aftershock sequences,and mainly carries out the following work:(1)According to the failure characteristics of low ductile RC frame,The finite element model of different response mechanism of low-ductility structural components is established by OpenSees The effects of shear failure in low-ductile beam-column joint zone,the bending-shear failure of the column,the degradation of strength and stiffness,and the bond-slip failure of longitudinal reinforcement at beam end on seismic response of low-ductile structure are analyzed.Fragility analysis for lowductile RC frames that consider different component response mechanisms.(2)Seismic performance analysis of low-ductile RC structures under different mainshock-aftershock sequences.In this paper,the real mainshock-aftershock sequences and the mainshock-aftershock sequences based on the repeated method are selected,and the influence of the aftershock directionality and the number of aftershocks on the fragility of the low-ductile structure is considered.The different mainshock-aftershock sequences are used as the ground motion input to calculate the fragility curve of the low-ductility structure under four kinds of limit states.The effects of different mainshock-aftershock sequences on the seismic performance of low-ductile structures are analyzed.(3)Aftershock fragility analysis for low-ductile RC frames that exhibit different mainshock-damaged states.The IDA analysis method is used to simulate the different damage states of low-ductile structures under the major earthquake.The probability demand model of aftershocks for low-ductile structures with different damage states under mainshocks is established.Then,the fragility of low-ductile structures with different damage states under the mainshocks is analyzed.The effects of different damage states of main shock on the vulnerability of low-ductility structure aftershocks are studied. |
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