Document: NUREG-0800
Document ID: 78905d69-1945-4638-99b9-2db68eb3da77
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070318.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
responses for major Category I structures are reviewed. In addition, the response spectra at major Category I equipment elevations and points of support are reviewed. 3. Procedures Used for Analytical Modeling The criteria and procedures used in modeling for the seismic system analyses are reviewed. The criteria and bases for determining whether a component or structure is analyzed as part of a system analysis or independently as a subsystem are also reviewed. 4. Soil-Structure Interaction The design earthquake motion is defined in the "free field," i.e., without the presence of structures, at the ground surface, at a real or hypothetical rock outcrop, or at a rock interface appropriate to the particular site. Because of the deformability of the supporting 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 isare usually assumed to be 3 symmetrical. g. The effect of pore water on structural responses, including the effects of variability of ground-water level with time. 3.7.2-3 DRAFT Rev. 3 - April 1996 h. Effects of partial separation or loss of contact