Document: NUREG-0800
Document ID: c165ebfe-8431-4d56-8bc9-97c2227d45bb
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070640311.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
ed on a case-by-case basis for acceptability. When the three components of earthquake motion are applied simultaneously, using a set of three artificial time histories, the statistical independence of the time histories should be demonstrated. See subsection II.1.B of SRP 3.7.1 for the acceptance criteria to demonstrate statistical independence. 7. Combination of Modal Responses. RG 1.92, describes acceptable methods for combination of modal responses, including consideration of closely-spaced modes and high-frequency modes, when the response spectrum method of analysis is used to determine the dynamic response of damped linear systems. Use of alternate methods are evaluated on a case-by-case basis for acceptability. When the modal superposition time history method of analysis is used, modal responses are combined algebraically, at each output time step. In accordance with RG 1.92, only modes with natural frequencies less than or equal to the ZPA frequency of the input spectrum are included in the modal superposition time history analysis. The contribution of the higher frequency modes to the total response is calculated by the missing mass approach. Since this contribution is in-phase with the input time history, it is treated as one additional modal response, that is scaled by the input time history normalized to the ZPA, and combined algebraically with the modal superposition time history solution at each output time step. 3.7.2-16 Revision 3 - March 2007 8. Interaction of Non-Category I Structures with Category I SSCs. All non-Category I structures should be assessed to determine whether their failure under SSE conditions could impair the integrity of seismic Category I SSCs, or result in incapacitating injury to control room occupants. Each non-Category I structure should meet at least one of the following criteria: A. The collapse of the non-Category I structure will not cause the non-Category I structure to strike a Category I SSC. B. The collapse of the