Nonlinear Seismic Response Characteristics of CAP1400 Nuclear Island Structure on Soft Rock Sites

Abstract

CAP1400 nuclear island structure is an advanced and novel nuclear power plant structure. In order to explore the seismic response characteristics of CAP1400 nuclear island structure on soft rock sites, a three-dimensional refined nonlinear seismic response analysis model was established for a soft rock foundation-nuclear island structure system using ABAQUS software. The influences of the input ground motion intensity and the frequency spectrum characteristics on the acceleration, relative displacement, and floor response spectrum, as well as the critical shear wave velocity of nonbedrock sites for CAP1400 nuclear island structure, were proposed. The results suggested that the increasing amplitude of the peak acceleration and relative displacement of nuclear island structure decreased as the soft rock site entered a nonlinear state, and the high-frequency components of the input ground motion became more abundant. Specifically, the earthquake response was the largest at the cooling water tank on the top of the shield building, which was the focus of the seismic research on nuclear island structure. Due to the influence of the ground motion frequency spectrum characteristics and the nonbedrock site effect, the peak acceleration, peak relative displacement, and acceleration response spectrum of the nuclear island structure showed different changing trends for the near-field and far-field ground motions. Based on the influence of the site shear wave velocity on the seismic response of nuclear island structure, it was recommended that the critical shear wave velocity of nonbedrock sites for CAP1400 nuclear island structure should be 1250 m/s, and the nuclear island structure-foundation dynamic interaction could be ignored at this time. The research conclusions could provide some technical support and theoretical basis for the construction and seismic performance research of CAP1400 and other nuclear power plants.

A new effective stress method for nonlinear site response analyses

“…The octahedral or generalized shear strain in 2D or 3D stress conditions is commonly used as the equivalent shear strain ( γ eq ) instead of shear strain 6,23 . The DCZ model using the generalized shear strain as the γ eq has been tested in 2D and 3D nonlinear seismic response analyses of large‐scale seabed site, submarine tunnel, underground structure, and nuclear island structure on soft rock during the three years 6,31,40,41,49 …”

“…To this end, based on the explicit algorithm method and parallel computing technology in ABAQUS/Explicit platform, 4 ,5 a user‐defined material subroutine VUMAT for the DCZ model combined with the conventional algorithm of γ eq , which is used in the total stress method for nonlinear site response analyses, has been successfully developed by Chen et al 6 to define the state of the material at the Gauss points within each element, and written in Fortran language. The VUMAT subroutine has been tested to conduct the 2D and 3D nonlinear seismic response analyses in a series of studies 31,40,41,49 . The proposed loose‐coupled effective stress method for nonlinear site response analyses in this article is also implemented in ABAQUS/Explicit platform.…”

“…To achieve convergence for the solution in the high nonlinearity of site response analyses, the time step size Δ t usually does not exceed 10 −5 seconds in an explicit dynamic analysis. The results of the 2D and 3D nonlinear seismic response analysis 4 , 5, 6, 31,49 have shown the availability and versatility of the above parallel computational method performed in ABAQUS/Explicit platform.…”