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:
l have characteristics consistent with characteristic values for the magnitude and distance of the appropriate controlling events defined for the corresponding uniform hazard response spectrum (UHRS). Option 2: Multiple Sets of Time Histories. As discussed in Section I.1.B and Section II.1.B of this SRP section, the use of multiple real or artificial time histories for analyses and design of SSCs is acceptable. For linear structural analyses, a minimum of four times histories should be used. For nonlinear structural analyses, the number of time histories must be greater than four and the technical basis for the appropriate number of time histories are reviewed on a case-by-case basis. This review also includes the adequacy of the characteristics of the multiple time histories. The response spectra calculated for each individual time history need not envelop the design response spectra. However, the multiple time histories are acceptable if the average calculated response spectra generated from these time histories envelop the design response spectra. An acceptable method to demonstrate the adequacy of a set of multiple time histories, in terms of enveloping requirements and having sufficient power over the frequency range of interest, is to follow the procedures described for Approach 2 presented in subsection II.1.B.ii of this SRP. When implementing Approach 2, the criteria in paragraphs (a) and (b) of this approach need to be satisfied for each of the time histories. The criteria in paragraphs (c) and (d) of this approach can be satisfied by utilizing the results for the average of the suite of multiple time histories. When calculating the response of structures (e.g., accelerations, member forces, and displacements) from linear analyses, the average value of the 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