Document: NUREG-0800
Document ID: b5a87a6e-5e73-493f-b8d9-5de2b5feba56
Document Type: srp
Title: SEISMIC DESIGN PARAMETERS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070317.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.1
CFR Part: 
CFR Title: 

Content:
Values The percentage of critical damping values used for Category Istructures, systems, and components SSCs is reviewed for both the OBE and the SSE. Critical damping is the 10 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 configuration. 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 existing in the system. A knowledge 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, concrete cracking, gaps, and other effects that tend to alter response amplitude. 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. Only the overall damping used for Category I structures, systems, and components SSCs is reviewed. When applicable, the basis for any damping values that differ from 11 those given in Regulatory Guide 1.61(Ref. 3) is reviewed. 12 DRAFT Rev. 3 - April 1996 3.7.1-4 3. Supporting Media for Category I Structures The description of the supporting media for each Category I structure is reviewed, including foundation embedment depth, depth of soil over bedrock, soil layering characteristics, design groundwater elevation, dimensions of the structural