Document: NUREG-0800
Document ID: 228b9b6e-c81e-4d76-9b8e-12f6c3bd7fa1
Document Type: srp
Title: and Regulatory Guide 1.92,(Reference 10) "Combining Modal Responses
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070336.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
and Spatial Components in Seismic Response Analysis" presents detailed criteria and guidance on this topicfor modal response combination methods which are acceptable to the staff.31 f. Analytical Procedures for Piping Systems The seismic analysis of Category I piping may use either a dynamic analysis or 32 an equivalent static load method. The acceptance criteria for the dynamic analysis or equivalent static load methods are as given in subsection II.2.a of this SRP section. g. 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 equipment items supported at two or more locations is to use an upper bound envelope of all the individual response spectra for these locations 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 (S ) is predicted by d 33 where S is the spectral acceleration in "g's" at the high frequency end of the a 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 DRAFT Rev. 3 - April 1996 3.9.2-12 structure in radians per second. The support displacements can then be imposed on the supported item in the most unfavorable combination. The responses due to the inertia effect and relative displacements should be combined by the absolute sum method. In the case