Document: NUREG-0800
Document ID: 10bc45c3-8e70-44ed-a57b-2dd08d4ef847
Document Type: srp
Title: SEISMIC SUBSYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070640313.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.3
CFR Part: 
CFR Title: 

Content:
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, Section 2, Volume 4.. If the ISM method is utilized, all of the criteria presented in NUREG-1061 related to the ISM method must be followed. In lieu of the response spectrum approach, time histories of support motions may be used as input excitations to the subsystems. The time history approach is considered to provide more realistic results as compared to 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. 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 reviewed on a case-by-case basis. 12. Seismic Category I Buried Piping, Conduits, and Tunnels. For seismic Category I buried piping, conduits, tunnels, and any other subsystems, the following items should be considered in the analysis: 3.7.3-6 Revision 3 - March 2007 A. Two types of groundshaking-induced loadings must be considered for design. i. Relative deformations imposed by seismic waves traveling through the surrounding soil or by differential deformations between the soil and anchor points. ii. Lateral earth pressures and ground-water effects acting on structures. B. The effects