Document: NUREG-0800
Document ID: 129133a3-2833-4da5-a564-052efbadbeb2
Document Type: srp
Title: but as applied to Category I subsystems.
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070319.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
he acceptance criteria provided in SRP Section 3.7.2, subsection II.8, are applicable to all seismic Category I SSCs at the system and subsystem level.12 9. Multiply-Supported Equipment and Components With Distinct Inputs Equipment and components in some cases are supported at several points by either a single structure or two separate structures. The motions of the primary structure or structures at each of the support points may be quite different. A conservative and acceptable approach for analyzing equipment items supported at 13 two or more locations is the uniform response spectrum (URS) technique: to use an An 14 upper bound envelope of all the individual response spectra for these locations is used15 to calculate maximum inertial responses of multiply-supported items. 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 structural response calculations or, as a conservative approximation, by using the floor response spectra. For the latter option the maximum displacement of each support is predicted by S = S g/ , where S is the d a a 2 spectral acceleration in "g's" at the high-frequency end of the spectrum curve (which, in turn, is equal to the maximum floor acceleration), g is the gravity constant, and is the fundamental frequency of the primary support structure in radians per second. The support displacements can then be imposed on the supported item in the most 3.7.3-5 DRAFT Rev. 3 - April 1996 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. Acceptable analysis methods that provide more realistic estimation of seismic responses are discussed in Section 2 of NUREG-1061 (Reference 4).16 In the case of