Document: NUREG-0800
Document ID: 29f5ac9f-4962-4021-913a-6375076e03fd
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340566.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
of the squares" (SRSS) method to predict the total floor response spectrum for that particular frequency (Ref. 7). If the three components of the motion are applied simultaneously (also see subsection II.6), the SRSS approach is not required. When a single artificial time history is used to generate the floor response spectra, all the provisions of Reference 7, including peak broadening requirements, shall apply. The use of single artificial time history should also be justified as outlined in subsection II.Lb of SRP Section 3.7.1. The use of multiple time histories to generate floor response spectra is reviewed and accepted on a case-by-case basis. Particularly, the basis for procedures used to account for uncertainties (by variation of para- meters) are evaluated. The same acceptance criteria are used for floor response spectra as are used for design response spectra in subsection II.1.b of SRP Section 3.7.1. For example, if the average response spectra 3.7.2-13 Rev. 2 - August 1989 generated from the multiple design time histories are used to envelop the design response spectra, then the average floor response spectra generated from the multiple analyses (each of which used one of the multiple design time histories) are used in design. Justification should be provided for the statistical relationship between input ground response spectra and output floor response spectra. The methods used for direct generation of floor spectra are reviewed and accepted on a case-by-case basis. 6. Three Components of Earthquake Motion Depending upon what basic methods are used in the seismic analysis, i.e., response spectra or time history method, the following two approaches are considered acceptable for the combination of three-dimensional earthquake effects (Ref. 8). a. Response Spectra Method When the response spectra method is adopted for seismic analysis, the maximum structural responses due to each of the three components of earthquake motion should be combined by taking