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
CFR Part: 
CFR Title: 

Content:
.2-2 Revision 3 - March 2007 2. Natural Frequencies and Responses. The staff reviews the significant natural frequencies and responses (accelerations, displacements, and member forces) for all seismic Category I structures. In addition, the in-structure seismic response spectra at the support locations for seismic Category I subsystems are reviewed. 3. Procedures Used for Analytical Modeling. The criteria and procedures used in modeling for the seismic system analyses (including structural material properties, modeling of member stiffness, modeling of mass [structural masses, live loads, floor loads, and equipment loads], modeling of damping, modeling of hydrodynamic effects, etc.) are reviewed. The criteria and bases for determining whether a structure is analyzed as part of a structural system analysis or independently as a subsystem are also reviewed. In addition, the method used to address floor and wall flexibility in the structural 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