Document: NUREG-0800
Document ID: c165ebfe-8431-4d56-8bc9-97c2227d45bb
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070640311.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
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CFR Title: 

Content:
at 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.). C. Nonlinear soil behavior. D. Coupling between the structures and soil. E. Lack of uniformity in the soil profile, which is usually assumed to be uniformly layered in all horizontal directions. F. Effects of the flexibility of soil/rock. G. Effects of the flexibility of basemat. H. The effect of pore water on structural responses, including the effects of variability of ground-water level with time. I. Effects of partial separation or loss of contact between the structure (embedded portion of the structure and foundation mat) and the soil during the earthquake. The procedures by which strain-dependent soil properties (damping, shear modulus, pore pressure development), layering, and variation of soil properties are incorporated in the analysis are reviewed. Assumptions for modeling the soil-structure system and computer program validation documents are also reviewed. 3.7.2-3 Revision 3 - March 2007 If applicable, the criteria for determining the location of the bottom boundary and side boundary of the soil-structure system model are reviewed. The procedures used in the SSI analysis to account for effects of adjacent structures, if any, on structural response are reviewed. To perform a seismic analysis for an SSI system, it may be necessary to have well- defined excitation or forcing functions applied at the model