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:
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) If 0.01 < Rm < 0.1, decoupling can be done if 0.8 > Rf > 1.25. (iii) If R > 0.1, a subsystem model should be included in the primary systWm model. If the subsystem is rigid compared to the supporting system, and also. is rigidly connected to the supporting system, it is sufficient to | include only the mass of the subsystem at the support point in the primary system model. On the other hand, in case of a subsystem supported by very flexible connections, e.g., pipe supported by hangers, the subsystem need not be included in the primary model. In most cases, the equipment and components, which come under the definition of subsystems, are analyzed (or tested) as a decoupled system from the primary structure and the seismic input for the former is obtained by the analysis of the latter. One important exception to this procedure is the reactor coolant system, which is considered a subsystem but is usually analyzed using a coupled model of the reactor coolant system and primary structure. c. Lumped Mass Considerations The acceptance criteria given under subsection II.1.a(iii) of this SRP section are applicable. d. Modeling for Three-Component Input Motion In general, three-dimensional models should be used for seismic analyses. However, simpler models can be used if justification can be provided that the coupling effects of those degrees of freedom that are omitted from the three-dimensional models are not significant. 4. Soil-Structure Interaction A complete soil-structure interaction (SSI) analysis must properly account for all effects due to kinematic and inertial interaction for surface or embedded structures. Any analysis method based on either a direct approach or a substructure approach can be used provided the following conditions are met: 3.7.2-8 Rev. 2 - August