Document: NUREG-0800
Document ID: 08c2f027-7464-43c9-8a18-8da0ade1cfb7
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A223.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
em 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 design ground motion response spectra at the foundation level (foundation input response spectra (FIRS)) are defined in the free-field, i.e., without the presence of structures, as described in SRP Section 3.7.1, and Interim Staff Guidance (ISG) DC/COL-ISG-01 and DC/COL-ISG-017. Performance-based free- field surface response spectra (PBSRS) are also defined at the free ground surface to ensure the performance adequacy of the soil columns used in the deterministic SSI analysis. The FIRS and PBSRS should be developed in a consistent manner. They are probabilistically determined performance-based spectra generated using the soil columns corresponding to the building. The properties of the soil columns usually consist of 60 or more randomized sets of properties similar to those used in the probabilistic seismic hazard analysis (PSHA) process. For sites with soil layers near the surface that will be completely excavated to expose competent material, and replaced with extended compacted backfill layers, the FIRS and PBSRS are determined considering the effect of the backfill layers in the site profiles that will exist after completion of excavation and backfilling. FIRS at the foundation should also be developed as free-field outcrop motions, not as in-column motions. Competent material is generally considered to be in-situ material having a minimum shear wave velocity of 1,000 feet/second (fps). 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