Document: NUREG-0800
Document ID: 45f5d841-54ef-4876-be3e-86eafc6ca90a
Document Type: srp
Title: Each calculated spectrum of the artificial time history is considered to envelop
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12352A305.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.0
CFR Part: 
CFR Title: 

Content:
responses from the multiple time histories may be used. When calculating the response of structures from nonlinear analyses (e.g., seismic evaluation of as-built structures), the average value of the responses from the multiple time histories may be used if at least seven nonlinear time history analyses are performed. Otherwise, the maximum value (i.e., envelope) of the individual responses from the multiple time histories should be used. 3.7.1-14 Draft Revision 4 - December 2012 In addition, if the extent of the nonlinear response is found to be significant or if the nonlinear response due to one or several time histories is found to be substantially different from the other results, then additional time histories should be considered. If there is a particular ground motion or time history analysis that dominates the response values, it should not be replaced with another motion or analysis to reduce the responses. Also, if a ratcheting effect is noted (e.g., increasing deformation with subsequent cycling of earthquake motion), then the system characteristics should be reviewed to ensure that they have been conservatively considered or the design should be revised to eliminate this behavior. 2. Percentage of Critical Damping Values. The specific percentage of critical damping values used in the analyses of Category I SSCs is considered to be acceptable if they are in accordance with RG 1.61. Damping values different from those listed in RG 1.61 (e.g., higher damping values) may be used in a dynamic seismic analysis if test data are provided to support them. These damping values will be reviewed and accepted by the staff on a case-by-case basis. In addition, a demonstration of the correlation between stress levels and damping values will be required and reviewed for compliance with the applicable regulatory position in RG 1.61. If other methods for correlation of damping values with stress level are used, they will need to be reviewed and accepted on a case-by-case