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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g, and 0.471 g respectively in <strong>the</strong> vertical direction. For <strong>the</strong> motions used in <strong>the</strong>se three tests,<br />
including both horizontal and vertical components, <strong>the</strong> dominant frequency is about 6 Hz, as<br />
shown by <strong>the</strong> corresponding response spectra plots (Figure 4-3 through Figure 4-5). The resonant<br />
frequencies measured in <strong>the</strong>se three tests are 6 Hz, 6 Hz, and 5.9 Hz, respectively, confirming that<br />
<strong>the</strong> input motions were specified to have <strong>the</strong>ir dominant frequency at <strong>the</strong> resonance. It should be<br />
noted that <strong>the</strong> resonant frequencies are slightly smaller than those measured in <strong>the</strong> elastic tests.<br />
The durations <strong>of</strong> <strong>the</strong> input motions <strong>for</strong> <strong>the</strong>se three tests are 82 seconds, and <strong>the</strong> time increments<br />
are 0.005 seconds.<br />
All input motions, recorded at <strong>the</strong> shaking table top, were found to include large drifting<br />
displacements, which may numerically reduce <strong>the</strong> accuracy <strong>of</strong> <strong>the</strong> calculated responses.<br />
There<strong>for</strong>e, <strong>the</strong> input motions are adjusted using a Lagrange-multiplier based correction algorithm<br />
[Borsoi, L. and Ricard, A. 1985], also termed in this report baseline-corrected or baseline<br />
correction whichever <strong>for</strong>m applies. Figure 4-6 shows <strong>the</strong> acceleration history, its Fourier<br />
trans<strong>for</strong>m, <strong>the</strong> velocity history, and <strong>the</strong> displacement history <strong>of</strong> <strong>the</strong> original record (in red dotted<br />
lines) and <strong>the</strong> baseline-corrected record (in blue solid lines) <strong>for</strong> <strong>the</strong> horizontal input motion <strong>of</strong><br />
DM4-1. The displacement <strong>of</strong> <strong>the</strong> original record appears to reach about 65 m in a monotonic<br />
fashion at <strong>the</strong> end <strong>of</strong> <strong>the</strong> time history, which is unrealistic and will probably shadow <strong>the</strong><br />
displacement responses that are in <strong>the</strong> magnitudes <strong>of</strong> millimeters. A similar drifting pattern can<br />
be observed in <strong>the</strong> original velocity time history, although it oscillates along its drifting path.<br />
After adjusted by baseline correction, <strong>the</strong> displacement and <strong>the</strong> velocity oscillate around zero,<br />
with <strong>the</strong> displacement variation nearly invisible in Figure 4-6. It is noticeable in <strong>the</strong> plot <strong>of</strong> <strong>the</strong><br />
acceleration time history that <strong>the</strong> original record (in red) is basically overlapped by <strong>the</strong> corrected<br />
record (in blue), indicating that <strong>the</strong> modification to <strong>the</strong> acceleration time history is small. This<br />
observation is also shown in <strong>the</strong> Fourier spectra plot, in which only <strong>the</strong> low frequency content is<br />
affected and <strong>the</strong> frequency content that excites <strong>the</strong> piping system <strong>the</strong> most is almost identically<br />
preserved by <strong>the</strong> baseline correction.<br />
The slight change in <strong>the</strong> acceleration time history during <strong>the</strong> baseline correction can be better<br />
noticed in Figure 4-7, in which <strong>the</strong> two time history records are plotted side by side. The 5%<br />
damping response spectra <strong>of</strong> <strong>the</strong> original and <strong>the</strong> baseline-corrected acceleration time histories are<br />
identical to <strong>the</strong> extent shown by Figure 4-7. More importantly, <strong>the</strong> change in <strong>the</strong> input motions<br />
due to baseline correction has virtually no effect in <strong>the</strong> analytical responses. In a preliminary<br />
analysis <strong>of</strong> <strong>the</strong> piping system using DM4-1 input motions, <strong>the</strong> displacement responses due to <strong>the</strong><br />
original and <strong>the</strong> baseline-corrected input motions are nearly identical (see Figure 4-8 <strong>for</strong> an<br />
example <strong>of</strong> displacement time history comparison). It should be noted that this preliminary<br />
analysis only serves as a sensitivity study <strong>of</strong> <strong>the</strong> baseline correction and its results do not<br />
necessarily match those in <strong>the</strong> result sections because subsequent modifications <strong>of</strong> <strong>the</strong> material<br />
and <strong>the</strong> finite element models were made.<br />
In addition, <strong>the</strong> removal <strong>of</strong> <strong>the</strong> residual displacement in <strong>the</strong> input motions <strong>for</strong> <strong>the</strong> analysis should<br />
not significantly affect <strong>the</strong> result comparison because <strong>the</strong> displacement measurements in <strong>the</strong><br />
experiment were taken as relative values with <strong>the</strong> top <strong>of</strong> <strong>the</strong> shaking table as <strong>the</strong> reference.<br />
There<strong>for</strong>e, all input motions used in <strong>the</strong> BNL analyses reported in <strong>the</strong> following are baselinecorrected.<br />
4.2.2 ANSYS Material Models<br />
Three kinematic hardening rules available in ANSYS have been studied in <strong>the</strong> piping analysis in<br />
<strong>the</strong> previous report [DeGrassi and H<strong>of</strong>mayer 2005]. In <strong>the</strong> analysis <strong>for</strong> <strong>the</strong> design confirmation<br />
method tests and also <strong>the</strong> ultimate strength tests, only <strong>the</strong> multi-linear kinematic hardening model<br />
and <strong>the</strong> Chaboche nonlinear kinematic hardening model [Chaboche 1986] are used in <strong>the</strong> final<br />
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