Seismic Design Method Of Reinforcement Concrete Frame Structures Considering Main Shock-aftershock Effects

Large numbers of aftershocks often occur after a main shock.Structures undergo plastic deformation after a main shock,which degrades stiffness and strength of the structure.Meanwhile,aftershocks after the main earthquake have the potential to aggravate the structural damage and even lead to collapse.Therefore,the study of seismic design method considering the effects of main shock-aftershock is particularly important.In this paper,different reinforced concrete structures are designed based on the design spectrum of the current seismic design code and the design of the main aftershocks.Based on these structures,the damage mechanism of the structure response under the corresponding fortification earthquake was studied.According to compare the collapse reserve coefficient of the structures,an earthquake-resistant design method considering the main and aftershock effects is proposed,based on the principle of equivalent collapse reserve.The main research results are as follows:1)Based on China’s current seismic design code and main shock-aftershock design spectrum,Sap2000 is used in this paper to design twelve RC frame structures with different seismic fortification intensity and different layers.Then,this paper uses OpenSees software to establish the two-dimensional frame of the above structural model,and the rationality of the model established by OpenSees is verified by comparing the structural modes and cycles.2)Fivty main shock-aftershock ground motions and their corresponding main shock ground motions are selected to conduct elasto-plastic analysis of structures in this paper.The results show that the effect of aftershocks will aggravate structural damage to a certain extent,and the additional damage follows the magnitude of the earthquake.In addition,by comparing different structural response indicators,the improved Park-Ang damage index has been found to be more sensitive to consider the effects of main shock-aftershock.3)The destruction mechanism of the reinforced concrete frame structure under the action of the main shock-aftershocks sequence is revealed,and it is found that the structure designed based on the main shock-aftershocks design spectrum has a smaller collapse reserve factor than the current code under the corresponding fortification earthquake.4)This paper uses IDA method and vulnerability analysis,combining with the collapse reserve coefficient CMR,to propose a seismic design method considering the effects of main shock-aftershock,so that the structure designed according to the main shock-aftershock design spectrum can achieve the same or similar CMR,thereby improving the collapse resistance of the structure under the action of the main shock-aftershock ground motion.So in this paper,the relationship between the collapse resistance of the structure and the period of the structure is theoretically derived,and the period prediction formula of the structure under main shockaftershocks based on the equivalent condition of collapse reserve is established,which can be used to guide the design of the structures under main shock-aftershocks.