Seismic damage evolution processes of the superstructure-integrated underground structure considering different seismic characteristics

The superstructure-integrated underground structure (SIUS) is a popular synthesis structure in urban city, which includes the aboveground part and underground part. The seismic responses of SIUS are influenced by the structural vibration of aboveground part and the soil deformation. Therefore, the seismic damage evolution processes of SIUS would be highly complicated, especially during different earthquakes with diverse seismic characteristics. In this paper, a finite element model of the soil-SIUS system is established. The representative ground motions corresponding to the actual site are selected. The seismic responses of both aboveground part and underground part in the SIUS are comprehensively studied, and the seismic damage evolution processes of the entire SIUS are clarified based on the seismic failure path of structural components. Furthermore, the influence mechanisms of seismic frequency characteristics and seismic input angles on the seismic responses and seismic damage evolution processes of SIUS are revealed respectively. The results show that the bottom aboveground part and outside underground part are typical vulnerable positions where the aboveground-underground interaction and soil-structure interaction are considerable respectively. The seismic damage evolution process would develop from bottom aboveground part to top aboveground part and develop from outside underground part to inside underground part. In addition, the aboveground part and underground part are demonstrated to be sensitive to the high-frequency and low-frequency respectively. The seismic input angle would have considerable influence effects on the underground part, and the seismic damage of the outside underground part would be more significant than that of the aboveground part with the increasing seismic input angle. This paper can develop an essential reference for the seismic design and of SIUS, and provide the important theoretical basis for the seismic performance evaluation of the large urban underground structures.