Document: NUREG-0800
Document ID: e53d553c-572a-4b29-a1c6-65d21835374f
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:
tural modeling is reviewed. 4. Soil-Structure Interaction. The earthquake ground motion response spectra (GMRS) are defined in the "free-field," i.e., without the presence of structures, at the ground surface. For sites with soil layers near the surface that will be completely excavated to expose competent material, the GMRS are specified on an outcrop or a hypothetical outcrop that will exist after excavation. Motions at this hypothetical outcrop should be developed as a free surface motion, not as an in-column motion. Competent material is defined as in- situ material having a minimum shear wave velocity of 1,000 feet/second (fps). Because of the deformability of the supporting media (rock or soil), the resulting motions at the foundation mat will differ from the corresponding free-field motions. This difference between the foundation mat motion and the free-field motion is known as the SSI effect. As applicable, the modeling methods (including technical bases) used in the seismic system analysis to account for SSI are reviewed. The factors to be considered in accepting a particular modeling method include: (1) the extent of embedment, (2) the layering of the soil/rock strata, and (3) the boundary of soil-structure model. All SSI analyses must recognize the uncertainties prevalent throughout the phenomenon, including: A. The random nature of the soil and rock configuration and material characteristics. B. Uncertainty in soil constitutive modeling (soil stiffness, damping, etc.).