Seismic Soil–Structure Interaction Analysis of Base Isolated Nuclear Building of Indian Pressurized Heavy Water Reactor Subjected to Coherent Ground Motion

Abstract

Research work of this study focuses on the seismic soil-structure interaction (SSSI) analysis of a base isolated nuclear building (NB) of the Indian pressurized heavy water reactor (IPHWR) under the action of coherent ground motion using the frequency domain approach. The seismic isolation of NB is achieved by installing lead rubber bearings (LRBs) below the raft. The base isolated NB is subjected to SSSI analysis in the frequency domain in order to take the influence of soil-structure interaction into account. LRB base isolators are numerically simulated as spring elements by assigning iterated equivalent linear stiffness. The seismic analysis of base isolated NB is performed using a conventional approach of fixed base analysis and the frequency domain approach of SSSI analysis to evaluate the effect of inclusion of SSSI on NB structures’ performance. This study also evaluates the implication of modeling isolators by assigning constant isolator stiffness as well as assigning equivalent linear stiffness to account for its nonlinear behavior under seismic excitation. Seismic responses in terms of in-structure response spectra and seismic displacements at representative locations of NB substructures are studied. The outcome of the study showed (1) base isolation of NB of IPHWR is achieved successfully by bringing down spectral accelerations and relative structural displacements of NB structure at target frequencies; (2) the conventional approach of fixed base boundary condition and assigning constant isolator parameters derived at isolator design displacement underestimates the structural responses in terms of spectral acceleration, frequencies, and displacements; (3) the conventional fixed base analysis approach fails to capture the spectral amplifications along its height at the fundamental frequencies of the various structure of NB; (4) discounting the SSSI effect along with equivalent iterative isolator parameters underestimates the structural responses marginally under horizontal excitation; and (5) the SSSI effect works like an isolation in the vertical direction and leads to reduced spectral accelerations in the vertical direction.