Document: NUREG-0800
Document ID: 1121c8ce-ab70-416c-9784-421014a1b25b
Document Type: srp
Title: SEISMIC DESIGN PARAMETERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1419/ML14198A460.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.1
CFR Part: 
CFR Title: 

Content:
such analyses are proposed. The adequacy of time histories used for the nonlinear analyses is reviewed. 2. Percentage of Critical Damping Values. The percentage of critical damping values used for the seismic analysis of seismic Category I SSCs 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 SSCs have energy losses that depend on numerous factors, such as material characteristics, stress levels, and geometric configurations. 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 function of the amount and type of damping inherent in the system. Knowledge of appropriate values to represent this characteristic is essential for obtaining realistic results in any 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, concrete cracking, gaps, and other effects that tend to alter response amplitudes. In real structures, it is often impossible to separate “true” material damping from system damping, which is the measure of the energy dissipation, from the nonlinear effects. Overall structural damping used in design is normally determined by observing experimentally the total response of the structure. Damping values assigned to members of seismic Category I SSCs, including material damping and system damping, are reviewed. When applicable, the basis for any damping values that differ from those given in RG 1.61, “Damping Values for Seismic Design of Nuclear Power Plants,” is reviewed. 3. Supporting Media for Seismic Category I Structures. The description of the supporting media for each seismic Category I