Document: NUREG-0800
Document ID: 6e0c1973-ed41-4000-9f50-3190607f8d57
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A354.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Draft Revision 4 - December 2012 (2) The 3 Hz frequency increment in the last row of RG 1.122, Table 1, applies up to the highest frequency of interest. This typically will be the PGA frequency of the design ground response spectrum, which in some cases may significantly exceed 33 Hz. (3a) When a single set of three artificial time histories is used as the input motion to the supporting structure, the in-structure response spectra are smoothed and broadened in accordance with the provisions of RG 1.122, to account for uncertainty. (3b) When multiple sets of three time histories, derived from actual earthquake records, are used as the input motion to the supporting structure, the multiple sets of ISRS already account for some of the uncertainty. Therefore, the provisions of RG 1.122, to account for uncertainty, do not strictly apply. The use of multiple sets of time histories to generate in-structure 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 parameters) are evaluated. The same acceptance criteria apply to the ISRS as apply to the design ground response spectrum, reviewed in subsection II.l.B of SRP Section 3.7.1. As an example, if the average of the multiple response spectra generated from the multiple design time histories is used to envelop the design ground response spectrum, then the average of the multiple in-structure response spectra generated from the multiple analyses (each of which used one of the multiple design time histories) are used in design. An evaluation of the statistical correlation between the input ground response spectrum and the output ISRS should also be provided. The methods used for direct generation of ISRS are reviewed and accepted on a case- by-case basis. 6. Three Components of Earthquake Motion. RG 1.92 describes acceptable methods for combining the responses due to three components of earthquake motion, for both the