Influence of Velocity-Pulse Characteristics in Near-Fault Mainshock-Aftershock Sequences on Subway Station Seismic Response

The influence of the velocity-pulse characteristics of the sequential earthquake on additional damage to the underground structures induced by aftershock warrants particular attention. In this paper, the pulse-like and non-pulse mainshock-aftershock sequences were constructed. A finite element model for the soil-subway station dynamic interaction was conducted. Furthermore, the average damage factor was employed to quantify the aftershock-induced vulnerability. The results indicate that pulse-like motions induce more significant horizontal displacements in columns and sidewalls, accompanied by increased differential settlements in slabs. For the non-pulse type, the aftershock results in a greater peak internal force response. Notably, under the peak acceleration of 0.20 g, the average damage factor of the upper column increases by 26.5% for the pulse-like aftershock, whereas it increases by 65.2% for the non-pulse type. The velocity-pulse effect on the damage extent of columns is evident, with the aftershock-induced incremental damage being most pronounced. Based on the correlation analysis of various intensity measures and the developed empirical model, the velocity spectrum intensity provides the optimal prediction for quantifying the damage degree of structures.