Document: NUREG-0800
Document ID: 585516eb-af20-45dc-a470-9638ec9381f3
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/ML0706/ML070640306.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.0
CFR Part: 
CFR Title: 

Content:
the design response spectrum when no more than five points fall below, and no more than 10 percent below, the design response spectrum. Studies indicate that numerically generated artificial ground acceleration histories produce PSD functions having a quite different appearance from one individual function to another, even when all these time histories are generated so as to closely envelop the same design response spectra. For example, the use of the available techniques of generating acceleration time histories that satisfy enveloping RG 1.60 spectra usually results in PSD functions that fluctuate 3.7.1-11 Revision 3 - March 2007 significantly and randomly as a function of frequency. It is also recognized that the more closely one tries to envelop the specified design response spectra, the more significantly and randomly do the spectral density functions tend to fluctuate and these fluctuations may lead to unconservative results for the response of SSCs. Therefore, when a single artificial ground motion time history is used in the design of seismic Category I SSCs, it must in general satisfy requirements for both enveloping design response spectra as well as adequately matching a target PSD function compatible with the design response spectra. Therefore, in addition to the response spectra enveloping requirement, the use of a single time history should also be justified by demonstrating sufficient energy at the frequencies of interest through the generation of PSD function, which envelops the target PSD function throughout the frequency range of significance. When RG 1.60 response spectra are used as design response spectra, the requirements for a compatible target PSD are contained in Appendix A to this SRP section. Target PSD functions other than those given in Appendix A can be used if justified. For design response spectra other than RG 1.60 response spectra, a compatible target PSD should be generated. For generation of target PSD in such cases, the