Document: NUREG-0800
Document ID: 7786a9e8-1ed1-44ea-a727-bfa570c49351
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A354.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Draft Revision 4 - December 2012 spurious spikes in the transfer functions above the frequencies of interest to the SSI analysis. (4) An evaluation should be performed to ensure that the frequency content of the ground motion input important to the SSI analysis is unaffected by the spurious vibration modes of the constrained excavated soil volume. Computer models of reduced size (e.g., quarter models) can also be used to obtain additional insight into the adequacy of an SSI analysis performed using the SM/MSM. In this case, direct comparisons between the SM/MSM and DM solutions are feasible and may provide valuable information that could be extrapolated to the full size model. There are advanced analytical methods currently being applied in the nuclear industry to develop seismic responses to high frequency ground motion inputs, incorporating the effect of ground motion incoherency. These methods might be used when a site acceptability determination is performed, as discussed in subsection II.4 of SRP Section 3.7.1. The phenomenon of ground motion incoherency in the free field has been investigated and characterized in terms of coherency functions, based on recorded earthquake data collected from dense array field tests. The ground motion incoherency effect on structural response is considered by incorporating coherency functions in analytical methods for SSI analyses. SSI analyses based on analytical methods that consider ground motion incoherency generally reduce structural response in high frequencies, compared to the response based on the traditional assumption of ground motion coherency. If the effect of incoherent ground motion is used to reduce the high frequency response, the potential effects of incoherent ground motion in increasing overturning and torsional responses need to be considered. The NRC issued Interim Staff Guidance (DC/COL-ISG-01) on May 19, 2008, describing methods acceptable to the staff for evaluating high frequency ground motion input. It