Document: NRC Regulatory Guide
Document ID: ad61f8a3-1cce-4446-9542-dcdda55c1ec6
Document Type: regulatory_guide
Title: Comprehensive Vibration Assessment Program for Reactor Internals During Preoperational and Initial Startup Testing + HISTORY - HISTORY 07/2015 – DG-1323 , Proposed Revision 4 03/2013 – Periodic Review of Revision 3 – No Issues Identified 11/2006 – DG-1163 , Proposed Revision 3 (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1508/ML15083A390.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.20
CFR Part: 
CFR Title: 

Content:
cases, checks on localized loading distributions, particularly in areas of expected high stress, need to be conducted to ensure conservative load mapping has occurred. c. Fatigue Analysis of Two-Sided Fillet Welds Before the use of general purpose finite element structural analysis computer codes, structural analysts and experimenters developed semi-empirical methods to ensure the structural reliability of fillet-welded connections subject to cyclic loading. The methods rely on the calculation of a “nominal” average stress plus linear bending stress through the thickness of the plate-type member at the fillet-welded connection, using hand calculations or simple computer models. A fatigue strength reduction factor (effective stress concentration factor) of 4 is then applied, based on extensive cyclic load testing. The resulting “peak” stress is used in the fatigue evaluation for cyclic loading. DG-1323, Page 26 Currently, structural analysts rely on mathematical simulation to solve complex problems. However, because of the unknown geometric condition at the root of a fillet weld, it is not practical to directly predict the stress field using mathematical simulation, regardless of the refinement of the local model. Using the stress results from a finite element analysis in the fatigue evaluation of fillet welds depends on the local geometric complexity and the level of model refinement at the double fillet weld connection. Two methods have been evaluated by the NRC staff, and found to be acceptable, with certain limitations on their application. The methods may be used, in conjunction with using appropriate multipliers, to achieve acceptable predictions of peak stress for use in a fatigue evaluation. The intent is to ensure a level of conservatism consistent with the traditional semi-empirical method that has been successfully employed for many years. The first method is analogous to the traditional method. The finite element analysis results from a global