Drift Ratio Limit for the Seismic Design of Underground Structures

The interlayer drift ratio of underground structures is an important seismic design index in China’s Seismic Design Code. However, existing elastic and elasto-plastic limit of drift ratio are adopted from ground structures, and those of underground structures have yet to be comprehensively studied. Based on the design practice of underground structures in China, a set of finite element pushover analysis is conducted on underground structures in this paper to investigate the seismic deformation of six common subway stations. A technique of combining beam elements with quadrilateral elements is utilized to capture the realistic elasto-plastic behavior of structural components. Computation results show that 1/550 and 1/1000 are appropriate elastic drift ratio limiting values for underground structures two stories or lower and underground structures three stories or higher, respectively. The elasto-plastic drift ratio limit of 1/250 that is adopted from China’s Code for Seismic Design of Building (CCSDB) is a conservative limiting value. The influence of buried depth and soil stiffness is also analyzed.