Document: NUREG-0800
Document ID: 0d1dd9a4-bcad-421f-a2f2-a33ef1c04988
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:
Revision 4 – September 2013 size in both the horizontal and vertical directions that is appropriate for adequately transmitting seismic motions over the frequency range of interest. Both the horizontal and vertical mesh size for the excavated soil model should satisfy the wave length requirement regardless of whether the model is being analyzed for the horizontal or vertical excitation. The geometric regularity of the mesh (aspect ratio and size) is also an important characteristic of the mesh to ensure the adequacy of the computational capability. In the SSI analysis of surface-supported structures using the substructure approach, or portions of embedded structures that are surface-supported, where there is no associated excavated soil volume, the guidance in the preceding paragraph is applicable to the mesh at the base of the surface supported structures. C. Input Ground Motion. The acceptance criteria for generating the input ground motion to be used in the SSI analysis are summarized in the following: i. For structures with either surface or shallow embedded foundations, the seismic input motions to the SSI analyses can be placed at the free ground surface or at the foundation level. For embedded structures, the seismic input should be specified at the foundation level as FIRS. In developing the corresponding ground motions at the surface, the potential effects of soft soil layers and/or compacted backfill layers should be considered. ii. Deterministic site response analyses are performed using at least three soil profiles defined as the Best Estimate (BE), Lower Bound (LB) and Upper Bound (UB) determined at the mean, and ± one sigma iterated velocity/damping profiles generated from the set of at least 60 randomized profiles used in the PSHA response evaluations. The UB high stiffness profile should make use of the LB damping properties for each layer of the profile. Similarly, the LB soft stiffness profile should make use of the higher damping properties.