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
CFR Part: 
CFR Title: 

Content:
pt of limited inelastic/nonlinear behavior when appropriate. The actual analysis, incorporating inelastic/nonlinear considerations, is reviewed on a case-by-case basis. 3.7.2-5 Rev. 2 - August 1989 a. Dynamic Analysis Method A dynamic analysis (e.g., response spectrum method, time history method) should be used. The use of the equivalent static load method is also acceptable if the method can be justified. To be acceptable, dynamic analyses should consider the following items: (i) Use of appropriate methods of analysis (e.g., time history, response spectrum, frequency domain) acccounting for effects of soil-structure interaction. (ii) Consideration of the torsional, rocking, and translational responses of the structures and their foundations. (iii) Use of an adequate number of masses or degrees of freedom in dynamic modeling to determine the response of all Category I and applicable non-Category I structures and plant equipment. (Caution should be exercised in reducing large static models to fewer degrees of freedom models (Ref. 3) for dynamic analysis.) The number is considered adequate when additional degrees of freedom do not result in more than a 10 percent increase in responses. Alternatively, the number of degrees of freedom may be taken equal to twice the number of modes. The adequacy of the number of modes is discussed below. (iv) Investigation of a sufficient number of modes to ensure participation of all significant modes. The criterion for sufficiency is that the inclusion of additional modes does not result in more than a 10 percent increase in responses. Responses associated with high-frequency modes may be important in some cases (where significant modes have frequencies greater than the frequency at which spectral accelerations return to the zero period acceleration; for example, 33 cycles per second in the case of structures, equipment, and components excited directly by Regulatory Guide 1.60 design spectra). Therefore, a demonstration that adequate