Document: NUREG-0800
Document ID: 29f5ac9f-4962-4021-913a-6375076e03fd
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340566.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
ed, bases and justification for not performing SSI analyses are reviewed on a case-by-case basis. If the SSI analysis is not required, the input motion at the base of the structures will be the design motion reviewed in'SRP Section 3.7.1. The acceptance criteria for the constituent parts of the entire SSI system are summarized as follows: a. Modeling of.Structure The acceptance criteria given under subsection II.3 of this SRP section are applicable. b. Modeling of Supporting Soil The effect of embedment of structure, ground-water effects, and the layering effect of soil should be accounted for. For the half-space modeling of the soil media, the lumped parameter (soil spring) method and the compliance function methods are acceptable. For the method of modeling soil media with finite boundaries, all boundaries should be properly simulated and the use-of types of boundaries should be 3.7.2-9 Rev. 2 - August 1989 . I justified and reviewed on a case-by-case basis. Finite element and finite difference methods are acceptable methods for discretization of a continuum. The properties used in the SSI analysis should be those corresponding to the low strains that are consistent with the realistic soil strain developed during the design earthquake. Use of high strain soil parameters needs to be adequately justified on a case-by-case basis. For structures supported on rock or rock-like material, a fixed base assumption is acceptable. Such materials are defined by a shear wave velocity of 3500 feet per second or greater at a shear strain of 10-3 percent or smaller when considering preloaded soil conditions due to the structure (Ref. 5). A comparison of fundamental natural frequencies of the fixed base and interacting structures can be used to justify the fixed base assumption (Ref. 6). c. Generation of Excitation System The control motion should be consistent with the properties of the soil profile. For profiles consisting of competent soil or rock, with relatively uniform