Document: NUREG-0800
Document ID: 8160c1fd-7cef-4c93-8e12-456019f2cfd2
Document Type: srp
Title: FOUNDATIONS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A267.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.5
CFR Part: 
CFR Title: 

Content:
the static type stability evaluation methods. Several DC applicants have resorted to more complex analytical methods to reduce the conservatisms inherent in the static approach. These methods rely on time history analyses using three directions of statistically-independent seismic loadings that are applied simultaneously. This approach eliminates the static analysis assumption that the maximum vertical and maximum horizontal demand forces occur at the same time. The oscillatory nature of the response in a seismic time history analysis may demonstrate that the specified factors of safety are maintained at each instant in time. If the linear time history analysis indicates that some sliding and uplift may occur, then a nonlinear time history analysis can be performed to include these effects. To provide guidance about the staff’s expectations when performing the time history evaluations discussed above, the guidance in SRP Section 3.8.5 was enhanced to address several issues: (1) since there is no single value to be used for the seismic demand, how the financial operations section (FOS) should be calculated in the evaluation, (2) for nonlinear analysis, how many time histories should be considered and how should the results from each of the time histories be evaluated, (3) the adequacy of 3.8.5-25 Revision 4 – September 2013 the mathematical model, (4) enhancement of the criteria for selection of the appropriate friction values, and (5) acceptance criteria if minimal sliding displacements do occur. 2. Revised SRP Section 3.8.5 II.4 “Design and Analysis Procedures” items E, J, and K, to include enhanced guidance to incorporate differential settlement and construction sequence aspects in the foundation design. The technical rationale for this change is as follows. Seismic Category I structures (foundations and superstructures) should be designed to take into account the additional member forces and moments that are induced by the combined effects of the