Document: NUREG-0800
Document ID: f58a3e4a-be8a-4b75-8b11-b41b7a54a500
Document Type: srp
Title: SEISMIC DESIGN PARAMETERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340564.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.1
CFR Part: 
CFR Title: 

Content:
stories may be real or artificial. 3.7.1-2 Rev. 2 - August 1989 Option 1: Single Time History Use of single time history is justified by satisfying a target power spectral density (PSD) requirement in addition to the design response spectra enveloping requirements. Option 2: Multiple Time Histories In lieu of the use of a single time history, multiple artificial or real time histories may be used for analyses and design of structures, systems, and components. The number and adequacy of time histories with respect to design response spectra are reviewed. In some instances, a nonlinear analysis of the structures, systems, and components may be appropriate (e.g., the evaluation of existing structures). Multiple time history analyses incorporating real earth- quake time histories are appropriate when such analyses are proposed. The adequacy of-time histories used in the analyses is reviewed. 2. Percentage of Critical Damping Values The percentage of critical damping values used for Category I structures, systems, and components is reviewed for both the OBE and the SSE. Critical damping is the amount of damping that would completely eliminate free vibration and is an important measure of the damping capacity of a structure. Vibrating structures have energy losses that depend on numerous factors, such as material characteristics, stress levels, and geometric configura- tion. This dissipation of energy, or damping effect, occurs because a part of the excitation input is transformed into heat, sound waves, and other energy forms. The response of a system to dynamic loads is a func- tion of the amount and type of damping existing in the system. A knowl- edge of appropriate values to represent this characteristic is essential for obtaining realistic results in dynamic analysis. In practical seismic analysis, which usually employs linear methods of analysis, damping is also used to account for many nonlinear effects such as changes in boundary conditions, joint slippage,