Simplified equivalent static methods for seismic analysis of shallow buried rectangular underground structures

Abstract

Simplified equivalent static methods are widely used in seismic design and analysis of underground structures. The relative shear deformation of the soil is usually considered as the main earthquake load in the existing simplified methods, including the free-field racking deformation method, flexible coefficient method, response displacement method, response acceleration method, and pushover analysis method. However, the inertia force of the overburden soil caused by the vertical earthquake motion does not attract sufficient attention in many design specifications. The recent studies revealed that the large vertical inertia force made a significant influence on the shear strength and deformation capacity of the support components in the underground structures, especially for the shallow buried ones. Firstly, based on the earthquake damage investigation of shallow buried rectangular underground structures and the analysis model of response displacement method (RDM), this paper proposes the vertical inertia force-response displacement method (VIF-RDM), in which the vertical inertia force of overburden soil is taken into account. The calculation methods of two critical parameters of the VIF-RDM are described in detail, including the coefficients of the foundation springs around the structure and the maximum vertical inertia force of the overburden soil. Afterwards, the integral vertical inertia force-response displacement method (IVIF-RDM) is put forward to reduce the computational complexity and calculation error of the foundation springs. The surrounding soil model is directly used to calculate the equivalent earthquake loads, which are caused by the relative displacement of the free field. The two proposed simplified methods and RDM are compared with the time-history analysis method (THAM) in a real underground structure. The results show a significant difference in the axial force of the central column between the two proposed methods and RDM. The proposed methods reflect the internal forces of the structure under the strong earthquake more accurately. Therefore, it can be used to evaluate the seismic safety performance of the shallow buried rectangular underground structures in the future.