SEISMIC PERFORMANCE AND INCREMENTAL DAMAGE ANALYSIS OF UNDERGROUND STRUCTURES UNDER MAINSHOCK-AFTERSHOCK EARTHQUAKES

Aftershocks occurring in a short time after a strong earthquake have an important impact on the structure damaged by the mainshock. Existing researches on seismic performance of underground structures are mainly based on the action of a single earthquake, and the understanding of the damage caused by aftershocks needs to be further improved. A soil-underground structure interaction model was established based on a typical two-story and three-span subway station to reveal the incremental damage and performance deterioration of the subway station subjected to mainshock-aftershock earthquakes. A set of 85 real mainshock records and mainshock-aftershock sequences from 14 real earthquakes were selected as inputs. Then, the seismic responses of underground structures were studied. The damage degree of the underground structure during the mainshock-aftershock earthquakes is obviously more serious than that when only the mainshock is applied. The increment amplitude and extension range of the structure damage are related to such factors as the peak acceleration ratio ξ, the characteristics of ground motion and the polarity of the main aftershock. Due to the cumulative effect of structural damage, the interlayer displacement of subway stations caused by aftershock excitation is greater than that of the mainshock when the seismic intensity of the mainshock is similar to that of the aftershock (ξ≈1.0). When the intensity of the mainshock is much greater than that of the aftershock (ξ≥1.4), the additional damage caused by aftershock to the underground structure is limited.