Endurance time analysis for seismic performance of underground structures subjected to mainshock-aftershock sequences

The seismic response analysis of subway underground structures only considers the impact of a single mainshock, ignoring the aftershocks, which may cause more serious secondary damage within a short time after strong earthquakes. To investigate the seismic performance of underground structures under sequential earthquakes and improve the understanding of aftershocks, we analyzed the dynamic response of subway station structures under mainshock-aftershock sequences. A typical two-story and three-span subway station was selected as the prototype, and a finite element model of a soil-underground structure interaction was established. Based on the basic concept of endurance time and design response spectrum of relevant seismic standards in China, an endurance time acceleration function was generated, and nine mainshock-aftershock sequences were constructed. Thereafter, the seismic responses of subway stations under the action of mainshock-aftershock sequences, such as lateral deformation characteristics and damage failure law, were discussed and analyzed. The results show that the endurance time method can be used as a new and efficient method to study the seismic performance of underground structures subjected to mainshock-aftershock sequences. The effects of aftershocks on the damage and lateral displacement of underground structures were preliminarily revealed. The structural deformation response of each layer varies greatly due to the different damage states of the mainshock. The maximum story drift theta of the structure increases with the increase of loading seismic intensity. From the perspective of seismic damage and relative deformation, the structural dynamic response, considering the effect of sequential earthquakes, is greater than that of the mainshock alone, which reflects the disadvantage of aftershocks in seismic design. The results provide a reference for seismic analysis and damage assessment of structures under sequential earthquakes.