Document: NUREG-0800
Document ID: 01f55174-7618-4db4-af9e-955638d7f076
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A223.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Revision 4 – September 2013 response spectra) from the time history motions resulting from the dynamic analysis of the supporting structure. The topics addressed are: A. Square-root-of-the-sum-of-the-squares (SRSS) Combination of the three ISRS in a given direction (e.g., x direction), developed from the output time histories from separate analyses of the three directions (x, y, z) of input motion. SRSS combination is not applicable, if the three directions of the input motion are applied simultaneously in a single analysis. B. Frequency increments for calculation of spectral accelerations. C. Spectrum smoothing and broadening to account for uncertainty. The guidance in RG 1.122 is augmented as follows: A. The SRSS combination applies to all cases where the three directions of input motion (two horizontal and one vertical) are analyzed separately. There is no longer a distinction made between symmetric and unsymmetric structures. B. 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 is the PGA frequency of the design ground response spectrum, which in some cases may significantly exceed 33 Hz. C. When a single set of three time histories is used as the input motion to the supporting structure, the ISRS are smoothed and broadened in accordance with the provisions of RG 1.122, to account for uncertainty. D. 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 ISRS 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