Document: NUREG-0800
Document ID: 94da2f11-6df6-47d0-a25e-edeb21a4d649
Document Type: srp
Title: 3.7.1-12
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1419/ML14198A460.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.0
CFR Part: 
CFR Title: 

Content:
target, where the ratio is calculated frequency by frequency, is only slightly greater than “1.” The aim is to achieve an accelerogram that does not have significant gaps in the Fourier amplitude spectrum, but which is not biased high with respect to the target. (a) The time history should have a sufficiently small time increment and sufficiently long duration. Records should have a Nyquist frequency of at least 50 Hz, (e.g., a time increment of at most 0.010 seconds) and a total duration of at least 20 seconds. If frequencies higher than 50 Hz are of interest, the time increment of the record should be suitably reduced to provide a Nyquist frequency (Nf =1/(2Δt), where Δt = time increment) above the maximum frequency of interest. The total duration of the record can be increased by zero packing to satisfy these frequency criteria. (b) Spectral acceleration at 5 percent damping should be computed at a minimum of 100 points per frequency decade, uniformly spaced over the log frequency scale from 0.1 Hz to 50 Hz or the Nyquist frequency. The comparison of the response spectrum obtained from the design ground motion time history with the target response spectrum should be made at each frequency computed in the frequency range of interest. (c) The computed 5 percent damped response spectrum of the acceleration time history should not fall more than 10 percent below the target response spectrum at any one frequency. To prevent response spectra in large frequency windows from falling below the target response spectrum, the response spectra within a frequency window of no larger than ±10% centered on the frequency should be allowed to fall below the target response spectrum. This corresponds to response spectra at no more than 9 adjacent frequency points defined in (b) above from falling below the target response spectrum. (d) The computed 5 percent damped response spectrum of the acceleration time history should not exceed the target response spectrum at any