Document: NUREG-0800
Document ID: 8f9a1788-18f3-4cf5-bdec-9e4e8971c97d
Document Type: srp
Title: -
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A354.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.7.2
CFR Part: 
CFR Title: 

Content:
Draft Revision 4 - December 2012 members should be reduced (e.g., using stiffness reduction factors). In other regions of the model where cracking does not occur, the same uncracked properties should be used, and the seismic analysis would be re-run. For those regions that are cracked, 7 percent damping may be used, while 4 percent damping should be used for the uncracked regions. The results of this analysis may be used as the basis for the ISRS, provided there are no additional members whose state of stress leads to further significant cracking in the model. If further significant cracking is identified in some of the remaining uncracked members, then reductions in the stiffness representation of those members should be made and a re-analysis of the model performed. If the state of stress in any cracked members demonstrates that the cracked members are no longer cracked, then it is not necessary to revise the cracked member properties back to the original uncracked properties. If any alternative methods are utilized, then adequate justification needs to be provided to demonstrate that the best estimate stiffness properties used for concrete are appropriate and that uncertainty associated with the best estimate stiffness values have been considered. In addition, it should be demonstrated that the SSI frequencies in both the horizontal and vertical directions are sufficiently below the amplified portion of the input design spectra so that if further cracking were to occur, then any reduction in stiffness would not increase the seismic demand. If the SSI frequencies fall above the amplified portion of the input design response spectra, then the analysis need to evaluate the effects of further concrete cracking since this may lead to higher demand loads on the structure. D. Representation of Floor Loads, Live Loads, and Major Equipment in Dynamic Model. In addition to the structural mass, mass equivalent to a floor load of 50 pounds per square foot should be included,