Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC

slightly wider resonant region towards the high frequency. The peaks are at a frequency of about
5 Hz, which is between the input dominant frequency of 4.5 Hz and the fundament frequency of
the pipe system of 6.09 Hz (6.2 Hz from test). The relative differences of both the maximum
spectra responses and the PGA’s are only about 2%.
DM4-1:
Comparisons for the DM4-1 test regarding the displacement D2, D4, and acceleration A2 are
provided in Figure 4-22 through Figure 4-24. The overall shapes and the peak responses of the
time histories agree excellently between the test and the analysis, with a maximum peak
difference of about 10% (over-predicted by the analysis). The analytical time histories appear to
be slightly less damped than the test. The Fourier spectra of the test displacements show a flat
region for frequencies above 20 Hz, suggesting white noise was recorded in the test. Unlike the
white noise for tests DM2-1 and DM2-2, the white noise for this test cannot be easily identified in
the time histories because the white noise is about five magnitudes smaller than the peak response.
The dominant responses, which are at a frequency of slightly less than 6 Hz, and most responses
for frequencies below 10 Hz compare especially well between the test and analysis. Both the test
and the analysis show discontinuities at around 1 Hz and 10 Hz in the Fourier spectra. There is
not a significant difference in the general trend of the displacement responses at the low
frequencies. The slight differences of the displacement responses at the low frequencies reflect
the difference in the residual displacements and the overall shapes, and may be due to the
baseline correction of the input motions. As discussed previously the baseline correction affects
mainly the low frequency range. The response spectra of the acceleration A2 for the test and
analysis match very well. The spectral response peaks are at a frequency of slightly less than 6
Hz, which is the same as the input dominant frequency and the fundamental frequency of the pipe
system (6.0 Hz from test DM4-1). The relative difference between the maximum spectra
responses is only about 12% (over-predicted by the analysis), comparing to the relative difference
of about 1% between the PGA’s.
DM4-2(1) (Restart):
This analysis considered the plasticity developed during DM4-1. Comparisons for the DM4-2(1)
with restart regarding the displacement D2, D4, and acceleration A2 are provided in Figure 4-25
through Figure 4-27. The overall shapes and the peak responses of the time histories agree
excellently between the test and the analysis, with a maximum peak difference of about 5%. The
analytical time histories appear to be slightly less damped than the test. The Fourier spectra of
the test displacements show a flat region for frequencies above 20 Hz, suggesting white noise was
recorded in the test. Unlike for tests DM2-1 and DM2-2, the white noise cannot be easily
identified in the time histories because the white noise is about 4~5 magnitudes smaller than the
peak response. The dominant responses, which are at a frequency of slightly less than 6 Hz, and
most responses for frequencies between 0.3~20 Hz compare especially well between the test and
analysis. Both the test and the analysis show discontinuities at around 1 Hz and 10 Hz in the
Fourier spectra. The differences of the displacement responses at the low frequencies reflect the
difference in the residual displacements and the overall shapes, and may be due to the baseline
correction of the input motions. The response spectra of the acceleration A2 for the test and
analysis match very well. The spectral response peaks are at a frequency of slightly less than 6
Hz, which is the same as the input dominant frequency and close to the fundamental frequency of
the pipe system (6.0 Hz from test DM4-2(1)). The relative difference of the maximum spectra
responses is only about 9% (over-predicted by the analysis), comparing to the relative difference
of about 2% of the PGA’s.
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