Document: NRC Regulatory Guide
Document ID: b6726dc6-2968-4ca9-a925-c831eaaecc69
Document Type: regulatory_guide
Title: 03/2007
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0702/ML070260029.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.61
CFR Part: 
CFR Title: 

Content:
of different connection types, use the lowest specified damping value, or as an alternative, use a “weighted average” damping value based on the number of each type present in the structure. 1.1.2 Operating-Basis Earthquake (OBE) If the design-basis OBE ground acceleration is selected to be less than or equal to one-third of the design-basis SSE ground acceleration, then a separate OBE analysis is not required. However, if the design-basis OBE ground acceleration is selected to be greater than one-third of the design-basis SSE ground acceleration, then a separate OBE analysis should be conducted. Table 2 provides acceptable damping values for the OBE analysis. Table 2. OBE Damping Values Structural Material Damping (% of Critical Damping) Reinforced Concrete 4% Reinforced Masonry 4% Prestressed Concrete 3% Welded Steel or Bolted Steel with Friction Connections 3% Bolted Steel with Bearing Connections 5% Rev. 1 of RG 1.61, Page 5 1.2 Special Consideration for In-Structure Response Spectra Generation The SSE damping values specified in Table 1 for linear dynamic analysis of structures have been selected based on the expectation that the structural response attributed to load combinations that include SSE will be close to applicable code stress limits, as defined in Section 3.8 of NUREG-0800 [Ref. 15]. However, there may be cases where the predicted structural response to load combinations that include SSE is significantly below the applicable code stress limits. Because equivalent viscous damping ratios have been shown to be dependent on the structural response level, it is necessary to consider that the SSE damping values specified in Table 1 may be inconsistent with the predicted structural response level. For structural evaluation, this is not a concern, because the stresses resulting from the use of damping-compatible structural response will still be less than the applicable code stress limits, as defined in Section 3.8 of NUREG-0800 [Ref. 15]. However, for