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:
rting rock or soil, the resulting motions of the base slab will differ from the corresponding free-field motions. This difference between the base slab motion and the free-field motion is known as the soil-structure interaction (SSI) effect. As applicable, the definition and location of the control motion and the modeling methods of SSI analysis used in the seismic system analysis and their bases are reviewed. The factors to be considered in accepting a particular modeling method include: (1) the extent of embedment, (2) the depth of soil, and (3) the layering of the soil strata. All SSI analyses must recognize the uncertainties prevalent throughout the phenomenon, including: a. Transmission of the. input motion to the site. b. The random nature of the soil and rock configuration and material characteristics. c. Uncertainty in soil constitutive modeling. d. Nonlinear soil behavior. e. Coupling between the structures and soil. f. Lack of symmetry in the soil deposits, which is usually assumed to be symmetrical. g. The effect of pore water on structural responses, including the effects of variability of ground-water level with time. h. Effects of partial separation or loss of contact between the structure and the soil during the earthquake. 3.7.2-2 Rev. 2 - August 1989 The procedures by which strain-dependent soil properties (damping, shear modulus, pore pressure), layering, and variation of soil properties are incorporated in the analysis are reviewed. If applicable, the criteria for determining the location of the bottom boundary and side boundary of the analysis model are reviewed. The procedures used to account for effects of adjacent structures, if any, on structural response in the SSI analysis are reviewed. To perform a dynamic analysis for an SSI system, it may be necessary to have a well-defined excitation or forcing functions applied at the model boundaries to simulate the earthquake motion. It is therefore required in such cases to generate an excitation