Elasto-plastic working states and seismic performance levels of frame-type subway underground station with two layers and three spans

The seismic performance of subway underground station has not been understood enough. According to the rules in the seismic codes of China, different stiffness ratios of underground structure to the surrounding soil foundation are designed. Considering the effects of the input earthquake waves, the elasto-plastic working states and seismic performance levels of a frame-type subway underground station are studied. Firstly, it is proved that the limit interlayer displacement angles of the subway underground station in the elastic or elasto-plastic working states are smaller than those of ground reinforced concrete frame structure. At the same time, the difference between the limit interlayer displacement angles of subway underground station is also smaller than that of ground reinforced concrete frame structure, which proves that the seismic performance of subway underground station is worse than that of ground reinforced concrete frame structure. According to the relationships among the interlayer displacement angles, the peak accelerations of the input ground motion and the stiffness ratios of structure to the nearby soil foundation, some empirical formulas are given to calculate the interlayer displacement angles of subway underground station. Finally, according to the relationship between the earthquake damage states and the interlayer displacement angles, the seismic performance of subway underground stations are divided into five levels and described.