Document: NUREG-0800
Document ID: 215ec1da-bdbb-48d3-b871-6010c1f4bc55
Document Type: srp
Title: SEISMIC SUBSYSTEM ANALYSIS REVIEW RESPONSIBILITIES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A239.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.3
CFR Part: 
CFR Title: 

Content:
us support locations. The URS is applied at all locations to calculate the maximum inertial responses of the equipment. This is referred to as the uniform support motion (USM) method. In addition, the relative displacements at the support points should be considered. Conventional static analysis procedures are acceptable for this purpose. The maximum relative support displacements can be obtained from the building structural response calculations. The support displacements can then be imposed on the supported equipment in the most unfavorable combination. The responses due to the inertia effect and relative displacements should be combined by the absolute sum method. The URS method described above can result in considerable overestimation of seismic responses. In the case of multiply- supported equipment in a single structure and/or spanning between structures, an alternate method that can be used is the independent support motion (ISM) approach. Guidance and criteria for the use of the ISM method is given in NUREG-1061, Volume 4, Section 2. If the ISM method is utilized, all of the criteria presented in NUREG-1061 related to the ISM method should be followed. In lieu of the response spectrum approach, time histories of support motions may be used as input excitations to the subsystems. The staff expects the time history approach to provide more realistic results than the USM or ISM methods. 10. Use of Equivalent Vertical Static Factors. The acceptance criteria provided in SRP Section 3.7.2, Subsection II.10, are applicable. 3.7.3-7 Revision 4 – September 2013 11. Torsional Effects of Eccentric Masses. For seismic Category I subsystems, when the torsional effect of an eccentric mass is judged to be significant, the eccentric mass and its eccentricity should be included in the mathematical model. The criteria for judging the significance will be determined on a case-by-case basis. 12. Seismic Category I Buried Piping, Conduits, and Tunnels. For seismic Category I