Document: NUREG-0800
Document ID: f58a3e4a-be8a-4b75-8b11-b41b7a54a500
Document Type: srp
Title: SEISMIC DESIGN PARAMETERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340564.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.1
CFR Part: 
CFR Title: 

Content:
ectra, as design spectra is also acceptable provided that their use is consistent with the information reviewed in SRP Section 2.5.2. 3.7.1-4 Rev. 2 - August 1989 To be acceptable, the design response spectra should be specified for three mutually orthogonal directions--two horizontal and one vertical. Current practice is to assume that the maximum ground accelerations in the two horizontal directions are equal. b. Design Time History The SSE and OBE design time histories to be used in the free field of the soil media shall be consistent with those developed or specified in Section 2.5.2. For both horizontal and vertical input motions, either a single time history or multiple time histories can be used. For linear structural analyses, using site-independent response spectra (e.g., Regulatory Guide 1.60), the total duration of the artificial accelerogram should be long enough such that adequate representation of the Fourier components at low frequency is included in the time history. The total time duration between 10 seconds and 25 seconds is required to adequately match the design response spectra at 0.4 Hz. The corresponding stationary phase strong-motion duration should be between 6 seconds and 15 seconds. If site-specific informa- tion reviewed in SRP Section 2.5.2 indicates duration estimates outside the above ranges, the site-specific values should be used. The rationale for selecting lower and upper limits on duration is presented in Reference 6. For nonlinear problems, duration estimates are reviewed on a case-by-case basis. Option 1: Single Time History To be considered acceptable, the response spectra of the artificial time history to be used in the free field must envelop the free-field design response spectra for all damping values actually used in the response analysis. When spectral values are calculated from the artificial time history, the frequency intervals at which spectral values are determined are to be small enough such that any reduction in