Document: NUREG-0800
Document ID: 1febfb39-661a-42d9-9d43-e8a0621eae35
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A223.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Revision 4 – September 2013 K* = {φ}T [K] {φ}, [K] = assembled stiffness matrix, j β = equivalent modal damping ratio of the jth mode, [ K ], [ M ] = the modified stiffness or mass matrix constructed from element matrices formed by the product of the damping ratio for the element and its stiffness or mass matrix, and {φ} = jth normalized modal vector. For models that take SSI into account by the lumped soil spring approach, the method defined by equation (2) is acceptable. For fixed base models, either equation (1) or (2) may be used. Other techniques based on modal synthesis have been developed and are particularly useful when more detailed data on the damping characteristics of structural subsystems are available. The modal synthesis analysis procedure consists of (1) extraction of sufficient modes from the structure model, (2) extraction of sufficient modes from the finite 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 SSI model are reviewed on a case-by-case basis. 14. Determination of Seismic Overturning Moments and Sliding Forces, Structure to Soil Pressures and Frictional Forces for Seismic Category I Structures. To be acceptable, the determination of the design seismic overturning moments and sliding forces, structure to soil pressures beneath the foundation and along side walls (including potential sliding and separation effects) and soil