Document: NUREG-0800
Document ID: 78905d69-1945-4638-99b9-2db68eb3da77
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070318.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
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CFR Title: 

Content:
inite element soil model, and (3) performance of a coupled analysis using the modal synthesis technique, which uses the data obtained in steps (1) and (2) with appropriate damping ratios for structure and soil subsystems. This method is based upon satisfaction of displacement compatibility and force equilibrium at the system interfaces and uses subsystem eigenvectors as internal generalized coordinates. This method results in a nonproportional damping matrix for the composite structure, and equations of motion have to be solved by direct integration or by uncoupling them by use of complex eigenvectors. Other techniques for estimating the equivalent modal damping of a soil-structure interaction model are reviewed on a case-by-case basis. Additionally, damping values derived from Appendix N to ASME Code Section III, Division 1, Code Case N-411-1 (Reference 12), insofar as they are compatible with the guidance provided in Regulatory Guide 1.84, are acceptable. 52 14. Determination of Category I Structure Overturning Moments To be acceptable, the determination of the design overturning moment should incorporate the following items: a. Three components of input motion. b. Conservative consideration of vertical and lateral seismic forces. Technical Rationale:53 The technical rationale for application of the above acceptance criteria to the seismic system analysis is discussed in the following paragraphs.54 3.7.2-19 DRAFT Rev. 3 - April 1996 1. General Design Criterion 2 requires, in relevant part, that SSCs important to safety be designed to withstand the effects of natural phenomena such as earthquakes, without loss of capability to perform their intended safety functions. GDC 2 further requires that the design bases reflect appropriate consideration for the most severe natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have