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

difference in the residual displacements and the overall shapes; these differences may be due to
the limitation of the material model as well as the baseline correction to the input motions. The
differences in the displacement Fourier spectra between 1 Hz and 2Hz and the strong cyclic
behavior of the analytical results between 10 Hz and 40 Hz may have contributed to the shape
and peak differences in the time histories. The analytical peak spectral response of the
acceleration A2 is lower than the test result by about 10% and the analytical PGA is lower than
the test result by about 8%. Nevertheless, the spectral responses from the test and the analysis
agree fairly well for the dominant frequency range around 3.6 Hz, which is the same as the
resonance frequency of the input motion and the fundamental frequency of the piping system.
The analytical response spectra shows a bump around 10 Hz, but the test does not.
In summary, although some comparisons of the analytical results for the US2-1 test are
reasonably good, most of the comparisons are not as accurate as those for the DM tests. It should
be noted that the comparisons for the DM4-2(2) test had already been shown to be less accurate
(mostly under-predicted) than those for the other DM tests that are subjected to lower level input
motions. The reason for the less accurate comparisons may be that the mono multi-linear
kinematic hardening model reaches shakedown for large input motions (large piping responses).
4.3.3.3 Difference of Elbow FE Modeling from DM Models
Because the differences in the piping system configuration between the US tests and the DM tests
are located outside of the Elbow 2 boundaries, the elbow shell model for the US tests is almost
identical to that for the DM tests. The only exceptions are the pipe diameter and the wall
thickness, which are 219.1 mm and 10.16 mm (average as-built values), respectively. Therefore,
Figure 4-37, showing the overall mesh of the elbow model, is valid for both the DM tests and the
US tests.
Figure 4-65 shows the strain gauge location and the four selected elements 145, 154, 315, and
324 in the elbow model for strain comparisons. The position of the strain gauges SE2C-7A and
SE2C-7H in the test were located between elements 154 and 324.
4.3.3.4 Input Motions for the Elbow Model
Figure 4-66 shows the input motions for the elbow model for US2-1. These motions were
generated from the piping system analysis described above. These input motions are designated
as DX, DY, and DZ for displacements and as RX, RY, and RZ for rotations. There are no test
results available for comparison of these input motions, and therefore observations regarding the
input motions for the elbow model will be qualitative.
As expected, the most significant vibrational input motions are displacement DX and rotation RZ,
because the shaking table excitation is only in the X direction for this test. DZ, RX and RY
oscillate in an apparently lower frequency than that of DX, DY, and RZ, indicating substantial
plasticity development rather than excited vibration. The rotational plastic deformations RX and
RY can reach magnitudes comparable to the major oscillating rotational deformation RZ. Figure
4-66 clearly shows that more severe plasticity in Elbow2 was caused in US2-1 than the DM tests.
4.3.3.5 Analysis of the Elbow Model and Result Assessment
Several attempts have been made in this study to obtain a complete execution of the analysis of
the elbow model (120 seconds) in ANSYS. However, the analysis could only reach as far as
about 77 seconds before ANSYS prematurely terminated with an output operation failure.
However, as shown in Figure 4-60, the significant part of the shaking table input motion has
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