Document: NUREG-0800
Document ID: d7cb8a38-878e-472d-94ad-0b40667eb30e
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A354.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Draft Revision 4 - December 2012 effect of in-phase and out-of-phase input motions can be considered in the SSI analyses by using plus and minus 1.0 times the magnitude of the input motions. Linear SSI analysis methods are acceptable if the ground contact ratio is equal to or greater than 80 percent. The ground contact ratio can be calculated from the linear SSI analysis using the minimum basemat area that remains in compression with the soil. If the ratio is less than 80 percent, then the effect of the nonlinearity due to the foundation uplift should be assessed, and if found important, then it should be accounted for in the seismic design, which is reviewed on a case-by-case basis. 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 provided that frequency variations and layering effects are incorporated. 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 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 that are consistent with soil strains developed in free-field site response analyses. For structures founded on materials having a shear wave velocity of 8,000 feet per second or higher, under the entire surface of the foundation, a fixed base assumption is acceptable. In the SSI analysis of embedded structures using the substructure approach, the finite element