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
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CFR Title: 

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total responses if the method of direct integration is used. b. A time history of acceleration (or other parameters of motion) or response spectrum used in design at the major plant equipment eleva- I tions and points of support. c. For multiple time history option, procedures used to account for uncer- tainties (by variation of parameters) and to develop design responses, including justification for the statistical relationship between input design response spectra and output responses. (For example, if the average response spectra generated from the multiple design time his- tories are used to envelop the design response spectra, then the aver- age responses generated from the multiple analyses are used in design.) 3. Procedures Used for Analytical Modeling A nuclear power plant facility consists of very complex structural systems. To be acceptable, the stiffness, mass, and damping characteristics of the structural systems should be adequately incorporated into the analytical models. Specifically, the following items should be considered in analytical modeling: a. Designation of Systems Versus Subsystems Major Category I structures that are considered in conjunction with the foundation and its supporting media are defined as "seismic systems." Other Category I structures, systems, and components that are not designated as "seismic systems" should be considered as "seismic subsystems." b. Decoupling Criteria for Subsystems 3.7.2-7 Rev. 2 - August 1989 It can be shown, in general, that frequencies of systems and sub- systems have a negligible effect on the error due to decoupling. It can be shown that the mass ratio, R and the frequency ratio, Rfs govern the results where Rm and Rf mre defined as: Rm = Total mass of the supported subsystem m Total mass of the supporting system R - Fundamental frequency of the supported subsystem f Dominant frequency of the support motion The following criteria are acceptable: (i) If Rm < 0.01, decoupling can be done for any Rf. (ii)