Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC
Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC
Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC
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Regulatory Guide 1.61 Revision 0 damping value <strong>of</strong> 2 percent provided margins that were generally at<br />
least 100 percent higher.<br />
The Ultimate Strength test was designed to produce a maximum elastically-calculated elbow stress <strong>of</strong><br />
24Sm and induce pipe failure. This occurred after five applications <strong>of</strong> <strong>the</strong> high-level earthquake input<br />
excitation. The Code analyses <strong>of</strong> this load case provided <strong>the</strong> highest stress margins. Analyses <strong>of</strong> <strong>the</strong><br />
piping system using design dimensions based on 1993 Code provided margins <strong>of</strong> 7.98 <strong>for</strong> 2 percent<br />
damping, 5.24 <strong>for</strong> 4 percent damping, and 4.67 <strong>for</strong> N-411 damping. Analyses based on <strong>the</strong> 1994 and<br />
2004 Code with 5 percent damping provided margins <strong>of</strong> 3.11. Since <strong>the</strong> measured elbow thickness from<br />
<strong>the</strong> test specimen were approximately 25% thicker than <strong>the</strong> design dimensions, <strong>the</strong> analyses were repeated<br />
using as-built dimensions. Due to <strong>the</strong> shift in piping system frequency and <strong>the</strong> higher wall thickness, <strong>the</strong><br />
stresses and stress margins were lower. The 1993 Code analyses provided margins <strong>of</strong> 6.35 <strong>for</strong> two<br />
percent damping, 4.50 <strong>for</strong> 4 percent damping, and 3.94 <strong>for</strong> N-411 damping. Analyses based on <strong>the</strong> 1994<br />
and 2004 Code with 5 percent damping provided margins <strong>of</strong> 2.63. Since a failure occurred at <strong>the</strong> highest<br />
stressed elbow, <strong>the</strong>se margins may be interpreted as failure margins based on stress level <strong>for</strong> this specific<br />
test. However, since <strong>the</strong> number <strong>of</strong> cycles in <strong>the</strong>se tests far exceeded <strong>the</strong> normal number <strong>of</strong> SSE cycles,<br />
some additional margin may be available. On <strong>the</strong> o<strong>the</strong>r hand, as discussed in Section 2.5, <strong>the</strong> seismic<br />
waves <strong>for</strong> <strong>the</strong> ultimate strength test were adjusted so that <strong>the</strong> dominant input motion frequency was close<br />
to <strong>the</strong> fundamental piping system frequency (on-resonance). There<strong>for</strong>e, it is possible that a different<br />
seismic input may result in a smaller margin.<br />
Fur<strong>the</strong>r discussion on <strong>the</strong> impact <strong>of</strong> 4 percent and 5 percent damping ratios on piping system responses is<br />
included in Appendix A.<br />
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