EVALUATION OF EARTHQUAKE-PROOF SAFETY DESIGN OF
PLANT STRUCTURE AND A CONCRETE METHOD
EVALUATION DE LA CONCEPTION DE LA SECURITE DES
OUVRGES DES INSTALLATIONS CONTRE LES SEISMES
ET UNE METHODE CONCRETE
Takenori Makita,Managing Director,
Tatsuya Hasegawa,Manager
Hajime Anzai, Deputy Manager
Nihonkai LNG Co. Ltd.
1612-32, Higashiko Seiromachi 1 Chome Kita-Kanbaragun
Niigata 957-0195 Japan
KeijiroYoshida, PM
Haruma Asakawa, PM
Hiroshi Sakagami, Manager,
Mitsubishi Heavy Industries, Ltd., Machinery Headquarters
3-1, Minatomirai 3 Chome Nishi-Ku, Yokohama 220-84 Japan
Dr.Tomomichi Nakamura, Chief Engineer,
Mitsubishi Heavy Industries, Ltd., Takasago Research & development Centre
1-1, Shinhama Arai-Cho 2 Chome Takasago, Hyogo 676 Japan
Shigemi Ochiai,Ph.D, CEO,
Jonquil Consulting Inc.
1-30, Takaido-Higashi 1 Chome Suginami-Ku, Tokyo 168-0072 Japan
ABSTRACT
Since the beginning of recorded history, earthquakes have brought some truly
appalling disasters upon mankind. In just the past few years we have had the Great
Hanshin Earthquake in Japan, the Izmit Earthquake in Turkey, and the Cumulative
Earthquake in Taiwan. These have brought untold damage to lifeline facilities needed for
public services. In particular, after the Great Hanshin Earthquake it took three days for
electric power to be restored and several months for the gas supply to return. This once
again recognized the need for an enough investigation on the safety design of public
utility facilities. Given this situation, we conducted studies and research over the space of
five years from 1996 on the earthquake-proof safety design of Nihonkai LNG Niigata
terminal, an important energy centre for the Japan Sea side of the country, based on the
lessons from the Great Hanshin Earthquake.
RESUME
Depuis le commencement de l’histoire, les séismes font des catastrophes meurtrières
sur les hommes. Juste ces dernières années sont survenus les séismes de Kobe au Japon,
d’Izmit en Turquie, et Celui Cumulé à Taïwan. Ils ont provoqué d’enormes dégâts sur les
infrastructures de vie requises pour les services publiques, et notamment dans le cas de
Kobe, il a fallu 3 jours pour le rétablissement de la distribution de l’énergie électrique, et
quelques mois pour le gaz de ville. L’événement a suscité à nouveau une prise de
conscience sur la nécessité d’une étude approfondie de la conception de la sécurité des
infrastructures d’utilité publique. Dans ce contexte et sur la base des leçons que l’on a
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tirées du tremblement de terre de Kobe, nous avons mené des études et des recherches
pendant 4 ans depuis 1996 sur la conception parasismique des installations de Nihonkai
LNG Co. Ltd. : un centre d’énergie important sur la côte de la mer du Japon de l’archipel.
1. Introduction
The object of the studies and research was to make certain the scale of earthquakes
and measures for improving the earthquake-proof safety design of various facilities. I
show one part of LNG facility whole view with Fig.1. To do this, we categorized the
importance of the facilities in terms of risk management, and organized earthquake
reinforcement measures in line with the level of importance. We collated the extent of
damage caused by the scale of earthquakes and theories on earthquake movement, and
installed strong motion seismographs in important points at each facility. We
incorporated data on actual earthquake behavior recorded by the seismographs in
earthquake-proof calculations.
As a result, we proved that
earthquake-proof safety design in
pipe racks needs to be reconfirmed.
We focused, in particular, on pipes
from a vaporizer and the racks
supporting them. We also analyzed
two-dimensional liquefaction of
subsoil and conducted earthquakeproof calculations taking account of
the effects of liquefaction. As a
result, we proved that the columns,
beams, pedestals, and foundation
concrete of pipe racks needs to be
reinforced. In the case of columns
Fig.1 C14 One part of facilities in Nihonkai
and beams, applying a cover
LNG Niigata Terminal
plateand thus increasing strength
can complete reinforcement. But
with the pedestals and foundation concrete, we proved that, if strengthened without due
care, the pedestals will become fixed and the piles subject not only to an additional axial
force but also to an excessive bending stress. Therefore, measures to reduce these are
needed.
To solve this, we developed a new method of reinforcing pedestals and pedestal
foundations while coupling them with a cushioning material. We made a 1/3-scale model
of an actual pipe rack and conducted simulations on a large-scale shaking table, proving
that the effects are considerable. We also conducted static loading tests on the 1/3-scale
model of an actual pipe rack and dynamic vibration tests on a large-scale shaking table.
The aim of this was to confirm the “ultimate strength of pipe racks with the developed
reinforcement measures” when applying the results of these studies and research to actual
earthquake-proof reinforcement of pipe racks. As a result, we were able to quantify the
ductility factor of pipe racks with earthquake-proof reinforcement.
Further, in order to confirm “the effect of liquefaction on pipe racks”, we conducted
large-scale shaking table experiments using the same model as above. As to the stress
acting on pipe racks due to liquefaction, we found that the stress occurring at points of
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contact between the pipes and the pipe rack is largest at the moment when the pipes are
pulled downwards simultaneously with the occurrence of liquefaction. If the ductility
factor of pipe racks calculated in this research is applied to pipe racks designed for
earthquake-proof reinforcement, the true yield strength of the pipe rack will be known
and it will be clear how great an earthquake force factor can be covered. If the ductility
factor is applied to earthquake-proof design in advance when designing new pipe racks,
optimal member selection will be possible. Also, with respect to the maximum stress
acting on the pipe rack due to liquefaction, it will be possible to reduce stress by placing
cushioning material at points of contact between the pipes and the pipe rack. We have
reflected these result and started earthquake-proof reinforcement work.
In this research, we describe the background to the pipe rack ductility factor
calculated by static loading tests and dynamic vibration tests on the large-scale shaking
table. We also discuss how this ductility factor should be applied to earthquake-proof
design to facilitate the assurance of earthquake-proof safety for pipe racks.
2. Description and Results of the Study and Research
2.1 Evaluation of the Impact on all the Facilities and Equipment in the Terminal
The study of earthquake-proof safety design of the LNG vaporizer and facilities and
equipment in the terminal was done by applying the risk management method to
categorize the importance of earthquake-proof safety design for each kind of facilities and
equipment. The risk management method was used to study the effects of an earthquake
on each kind of component equipment and piping of the plant to assess the importance of
each kind in guaranteeing safety and maintaining plant facilities and to evaluate the
impact of the failure of each kind on the other kinds, and based on the results, rank each
according to its importance and the possibility of it being a weak point within the
terminal. Figure 2 shows an example of screening results. As Figure 2 shows, the
screening assessed 5 factors by assigning points from 1 to 5 for each factor, with 5 points
representing the most dangerous state of each factor.
Fig. 2 The result of screening
The final risk evaluation was represented by the total
of the points given to all five factors and ranking the
object with the highest score as the one with the greatest
influence. Table 1 shows facility from big order of
influence degree to the fifth. This study has revealed that
earthquake damage to the low pressure ORV would
cause the most harm to the rest of the plant equipment.
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Table.1 Evaluation of risk
And knowledge about the effects of earthquakes on the principal equipment was
finalized by summarizing earthquake design methods and earthquake force coefficients
when the facilities and equipment were designed in order to organize the earthquake
coefficients. Because it has been reported that almost all the cases of damage to ordinary
plants caused by the Hanshin Earthquake Disaster were LNG tank failure caused by the
diamond buckling of cylindrical tanks, bending of pipe racks by liquefaction, and oil
leaks caused by cracked piping, earthquake response analysis of LNG tanks was
performed using the El Centro earthquake waves. As a result of the calculation, strong
motion seismographs were installed near the LNG tank foundations and near pipe racks
in the base to observe behavior during an earthquake. These have provided records of 10
earthquakes.
2.2 Study of Earthquake-proof Safety Design of Facilities and Equipment around the ORV
Following the research described in 2.1, an earthquake-proof safety design analysis of
the facilities and equipment around the ORV was performed with particular focus on the
piping connected to the ORV and the pipe racks supporting that piping. The analysis
estimated the amplification properties and natural period of the ground to evaluate the
equipment’s interaction with the ground, evaluated the possibility of liquefaction, and
hypothesized the earthquake behavior of the pipe racks. The study provided two results.
(1) Measurements of the micro tremors of the ground and analysis of the frequency
properties of the earthquake waves in strong motion records have shown that the natural
periods of the ground around the ORV include a natural period close to 1.0 second that
suggests the possibility of liquefaction occurring.
Therefore, the 1.0 second natural period of the ground was used to perform an
approximate liquefaction analysis, revealing that liquefaction will occur at a depth near
10 m. (2) It was discovered that it is necessary to do earthquake-proof reinforcement of
the columns, beams, and pedestal foundations of the pipe racks. Site surveys to visually
inspect for deterioration over time and an assessment of the present design allowable
stress has been performed to confirm the allowance against earthquakes of all the pipe
racks in the terminal.
2.3 Study of Liquefaction Analysis and Earthquake-proof Reinforcement Method
Following the study in 2.2, El Centro earthquake waves were used to perform twodimensional liquefaction analysis of the ground around the ORV based on input
accelerations of 1 m/s2 and of 3 m/s2. The results revealed that in the ground inside the
terminal, there is a high possibility of liquefaction occurring at an earthquake input
acceleration of about 1 m/s2. The calculation results have shown that liquefaction would
pull the piping around the ORV towards the ground and transmit bending moment to the
pipe racks supporting this piping. Adding the stress this generates to the pipe racks to
perform earthquake calculations confirmed that there would be little leeway between the
earthquake force coefficient and the allowed stress of the beams and the surrounding
columns at the connections between the piping from the ORV and the pipe racks. They
reveal that the stress on the base plates is severe and that they could slide laterally. Based
on these results, the earthquake-proof safety design of the column and beam members
was successfully maintained by installing cover plates on them to increase their strength.
The earthquake strength of the pedestal was increased by earthquake-proof reinforcement
them with reinforced concrete in order to strengthen there pedestal foundation concrete
and prevent buckling of the base plates, but new bending moment is generated in the
foundation.
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2.4 Study on Effective Pedestal Earthquake-proof Reinforcement
Next, to increase the strength of the pedestal in order to lower the axial force and
bending stress generated in the pedestal and
piles by the earthquake-proof reinforcement of
the pedestal foundations, a method involving
inserting cushioning materials between the
reinforced concrete and the columns in order
to prevent the transmission of bending
moment to the foundation was devised. Then
to verify this proposed method’s effects, a 1/3scale specimen of an actual pipe rack was
prepared and used for a vibration test on a
three-dimensional shaking table. Figure 3
Fig.-3 Vibration test on a three-dimensional
shows this test. Three facts were learned from
shaking table
its results. Also Table 2 shows a characteristic
of vibration stand.
Table 2 A characteristic of a three-dimensional shaking table vibration stand
Performance of experimental devices
A limit to experimental devices
Horizontal X-Direction 120 ton • g
Horizontal Y-Direction 60 ton • g
Vertical Z-Direction
120 ton • g
Horizontal Direction
about 20m/s2 (60 ton Inertia load)
Scale of experimental devices
Vertical to experimental devices
about 20m/s2 (60 ton Inertia load)
Size of experimental devices 6 ×6m×1m
Weight of experimental devices
20 ton
Load Weight
100 ton (max)
Frequency range
0~50 Hz
(1) Without earthquake-proof reinforcement, the earthquake wave input caused the bases
plate to be pulled up by the pullout force of the anchor bolts of the pipe rack pedestal,
but earthquake-proof reinforcement the pedestal with concrete prevents the base plate
from rising.
(2) When the base plate has been earthquake-proof reinforcement with concrete, the
stress of the anchor bolts is lowered.
(3) Earthquake-proof reinforcement the pedestal of the pipe racks with concrete and
inserting cushioning materials between the pipe rack pedestal and the concrete is an
effective method that prevents the generation of new bending moment from the
pedestal foundations.
To summarize these results, it was possible to increase the earthquake-proof safety
design of the columns and beams of the pipe racks by installing cover plates on parts with
stress extremely close to the design allowed stress of 1.0 accounting for overall balance,
and by increasing the earthquake-proof safety design of the pedestal foundations by
inserting cushioning materials between the pedestal and the poured concrete and
earthquake-proof reinforcement the pedestal foundations.
3. Evaluation of Strength and Safety of the Pipe Racks after Reinforcement
As stated in 2.4, the earthquake-proof reinforcement sharply lowered the design
allowed stress from 1.0, maintaining the safety of the pipe rack. In order to quantitatively
clarify the earthquake-proof safety design of the overall pipe racks from the earthquake
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design perspective instead of only performing earthquake-proof reinforcement of the pipe
racks in order to shift the design allowed stress to the safe side, 1/3- scale specimens were
used for earthquake-proof safety design testing to study the following two points.
(1) Specimens of pipe racks before earthquake-proof reinforcement and racks after
earthquake-proof reinforcement were used for static loading testing in order to clarify
which specimen exceeded the yield point and estimate their strength (ultimate strength).
Figure 4 and Figure 5 shows these tests. The testing of the specimens without earthquakeproof reinforcement revealed that under the loading, the stress of the members gradually
rose and the anchor bolts exceeded the yield point to reach the plasticity range. Even
Fig.-4 Static load test without
reinforcement model (Type-0)
Fig.-5 Static load test with
reinforcement model (Type-3)
though loading continued, only the strain increased until ductile failure of the anchor
bolts occurred. This time is assumed to be the failure point. This result confirmed that the
ultimate strength of a rack without earthquake-proof reinforcement is determined by the
strength of its anchor bolts. Figure 6 shows the state of a pedestal that was broken by
ductile fracture of the anchor bolts. In the design of an actual pipe rack, pedestals are
designed as either pin connections or as semi-anchored. It was confirmed that the
experimental results conform to the present design. In the case of a specimen with
earthquake-proof reinforcement on the other hand, the compression braces exceeded the
plastic range, and then although the loading
continued, only the strain increased until the braces
were completely buckled. Figure 7 shows the state
where the compression braces were completely
buckled and Figure 8 shows a case where the beams
buckled. It is assumed that the compression side
braces ultimately buckled, because the earthquakeproof reinforcement of the pedestal foundation
increased the strength of the anchor bolts and because
plates were installed on columns and beams to
strengthen them. It was not possible to confirm the
Fig. 6 Pedestal was broken by
curvature of the columns, but the overall specimens did
ductile fracture (Type-0)
not topple.
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Fig.-7 The compression braces were
completely buckled by the static
load test (Type-3)
Fig.-8 The beams buckled by the
static load test (Type-3)
The results of the static loading testing have shown that the ductility factor can be
almost tripled by earthquake-proof reinforcement.
(2) Type 3 specimens were used to perform dynamic vibration testing on a large shaking
table in order to study the dynamic stress that occurs at the contact points of the piping
and the pipe rack the instant that the piping is pulled downwards as liquefaction occurs.
Figure 9 and Figure 10 shows this experiment. Because Figure 10 shows the test while it
was in progress, the piping on the racks shakes violently so that it appears as if there are
two pipes.
Fig.-9 The effect of liquefaction on
pipe; Rack (Type-3) before vibration
Fig.-10 The effect of liquefaction on
pipe; Rack (Type-3)
The test results show that the stress on the piping was extremely large. Because the
piping on the racks on the shaking table was wrapped with cushioning material but not
with buffer material, its impact with the rack in response to the earthquake waves caused
large stress, and it is a phenomenon that cannot be accounted for by the calculations.
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4. Execution Design of Earthquake-proof Reinforcement and Earthquake-proof
Reinforcement Work
The execution design done to prepare for the earthquake-proof reinforcement
stipulated that cover plates be installed on columns and beams with little leeway between
the design allowable stress and the present design earthquake force coefficient accounting
for the ductility rate found in paragraph 3, that cushioning materials be inserted between
the pedestal and the poured concrete of the pedestal foundation and that these pedestal
foundations be earthquake-proof reinforcement with concrete. Earthquake-proof
reinforcement of part of the pipe rack began based on this earthquake-proof
reinforcement design. Figure 11 and Figure 12 shows the scene of the earthquake-proof
reinforcement work.
Fig.-12 The earthquake-proof
reinforcement work
Fig.-11 The earthquake-proof
reinforcement work
The above earthquake-proof reinforcement work has guaranteed the earthquake safety
of the pipe racks at Nihonkai LNG Niigata terminal, an important energy centre for the
Japan Sea side of the country.
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