Document: NUREG-0800
Document ID: 29f5ac9f-4962-4021-913a-6375076e03fd
Document Type: srp
Title: SEISMIC SYSTEM ANALYSIS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340566.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
be necessary to have a well-defined excitation or forcing functions applied at the model boundaries to simulate the earthquake motion. It is therefore required in such cases to generate an excitation system acting at the boundaries such that the response motion of the soil media at the plant site in the free field is identical to the design ground motion. The procedures and theories for regeneration of such an excitation system are reviewed. Any other modeling methods used for SSI analysis are also reviewed as is any basis for not using an SSI analysis. 5. Development of Floor Response Spectra The procedures for developing floor response spectra are reviewed. There are several methods for generating in-structure response spectra. One method makes use of time history analysis by considering single or multiple (real or artificial) ground time histories which have spectra that, essentially, envelop the design response spectra. Another method involves a group of analysis techniques generally referred to as the direct solu- tion methods for the generation of in-structure response spectra. These techniques do not involve time history analysis. The basis and justifica- tion for the use of either of the above methods are reviewed. 6. Three Components of Earthquake Motion The procedures by which the three components of earthquake motion are considered in determining the seismic response of structures, systems, and components are reviewed. 7. Combination of Modal Responses When a response spectrum method is used for calculating the seismic response of structures, systems, or components, the phase relationship between various modes is lost. Only the maximum response for each mode can be determined. The maximum responses for modes do not in general occur at the same time, and these responses have to be combined according to some procedure selected to approximate or bound the response of the system. When a response spectrum method is used, the description of the procedure for