A nonlinear soil-structure interaction analysis technique based on seismic isolation design response spectrum for seismically isolated nuclear structures with rigid basemat

Abstract

Seismic Analysis of Safety-Related Nuclear Structures (ASCE 4-16) offers a two-step nonlinear soil-structure interaction analysis procedure for seismically base-isolated structures based on the seismic isolation design response spectrum. The two steps are (I) development of seismic isolation design response spectrum at the foundation level of an isolated structure using frequency domain soil–structure interaction (SSI) analysis for an equivalent linear SSI system and (II) nonlinear time domain analysis of the isolated structure using foundation input motions, which is consistent with the seismic isolation design response spectrum. In step II, the rocking component of the structure shall be considered when its effects are significant. However, the ASCE 4-16 does not present how to consider the rocking input. In this study, we propose a method of taking account the rocking component of a base-isolated structure with rigid basemat. Specifically, this paper presents a method of developing rocking input motion that is fully coupled with horizontal input motion at the base of the isolated structure. The method was verified by comparing numerical results using the rocking input for a base-isolated nuclear power plant with rigid basemat on a compliant soil medium with those of a refined nonlinear response history analysis.