Enhanced Simplified Method for Pseudostatic Analysis of Seismic Internal Forces in Rectangular Underground Structures

Abstract

Current simplified analysis methods for rectangular underground structures subjected to earthquake action present in US design codes or analogous documents are based on the structure shear distortion assessment by means of closed-form solutions of the so-called racking coefficient, and then evaluation of the structure internal forces through the analysis of a simple frame subjected to imposed displacements. However, current formulations for these methods provide inaccurate results in terms of internal forces when compared with numerical analyses and experimental measures, especially for the more flexible structures compared with surrounding ground corresponding to large underground spaces like metro stations. This paper addresses this issue and proposes an improved yet simple method to compute internal forces for deeply and shallowly buried rectangular underground structures subjected to earthquake action. The proposed method is proven to be more accurate predicting internal forces than current simplified methods when compared with finite-element analyses for structure flexibility ratios 0<FR≤120.