Applsci 12 08390 (3)

The acceleration response of the seismic storage tank increases approximately linearly along the direction of height, and the seismic isolation bearing has a significant seismic isolatio

Citation:Chen, Z.; Xu, Z.; Teng, L.;

Fu, J.; Xu, T.; Zhao, Z Experimental

and Numerical Investigation for

Seismic Performance of a Large-Scale

LNG Storage Tank Structure Model.

Appl Sci 2022, 12, 8390 https://

doi.org/10.3390/app12178390

Academic Editors: Panagiotis

G Asteris, Nikola Grgi´c and

Goran Baloevi´c

Received: 18 July 2022

Accepted: 12 August 2022

Published: 23 August 2022

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applied

sciences

Article

Experimental and Numerical Investigation for Seismic

Performance of a Large-Scale LNG Storage Tank

Structure Model

Zengshun Chen 1 , Zhengang Xu 1, *, Lingxiao Teng 2 , Jun Fu 1,3,4 , Tao Xu 1,5 and Zhihang Zhao 1, *

1 School of Civil Engineering, Chongqing University, Chongqing 400045, China

2 Science and Technology Quality Department, Chongqing Design Institute Co., Ltd., Chongqing 400015, China

3 Key Laboratory of Icing and Anti/Deicing, China Aerodynamics Research and Development Center, Mianyang 621000, China

4 Construction Management Department, Construction of Five Investment Management Company, Changsha 410116, China

5 Management Department, Construction of Chongqing High-Tech Building Materials Company, Chongqing 401431, China

* Correspondence: zhengangxu@cqu.edu.cn (Z.X.); zhaozhihang@cqu.edu.cn (Z.Z.)

Abstract:As special equipment for storing energy, the safety performance of liquified natural gas (LNG) storage tanks under earthquake action is extremely important To study the dynamic charac-teristics of the large-scale LNG storage tank structure and the dynamic response under earthquake action, the shaking table test and numerical simulation analysis of the LNG storage tank structure model are carried out The results of the shaking table test demonstrate that the natural vibration frequency of the tank model is significantly reduced after the isolation measures are taken The acceleration response of the seismic storage tank increases approximately linearly along the direction

of height, and the seismic isolation bearing has a significant seismic isolation effect on the acceleration

of the storage tank The numerical simulation results show that the seismic responses and their spectral characteristic curves of the numerical model and the shaking table test are the same, which verifies the feasibility and rationality of the numerical model After seismic isolation measures are taken, the seismic responses of large-scale LNG storage tanks, such as base shear force, overturning bending moment and acceleration, are reduced to varying degrees, but the displacement of the storage tank increases to some extent When carrying out the seismic isolation design of LNG storage tanks, it is necessary to focus on the displacement of the storage tank to prevent damage of the auxiliary pipeline led by excessive displacement

Keywords:LNG storage tank; shaking table test; dynamic characteristics; dynamic response; seismic performance

1 Introduction

The large liquified natural gas (LNG) storage tank is an important energy storage equipment, which is widely used in chemical raw material production and energy supply Typically, LNG storage tanks are built in coastal areas to receive LNG from maritime transport However, poor geological conditions in coastal areas, which are prone to suffer from foundation liquefaction [1], result in settlement and inclination of buildings The safety of large LNG storage tanks is always threatened by earthquakes Once a severe earthquake comes, large LNG storage tanks will suffer from a tremendous overturning bending moment and dynamic hydraulic pressure, which may lead to damage to the storage tank [2] and buckling failure of the inner tank [3,4] This can lead to leakage of LNG, which can result in fires and explosions [5–7] It is critical that large LNG storage tanks remain intact during the course of earthquakes Therefore, it is of great practical

Appl Sci 2022, 12, 8390 https://doi.org/10.3390/app12178390 https://www.mdpi.com/journal/applsci

Appl Sci 2022, 12, 8390 2 of 20

significance and engineering value to study the seismic performance of large-scale LNG storage tanks

Liquid−solid interaction is the most obvious difference between storage tanks and conventional civil structures (such as houses and bridges) Under the external excitation, the liquid will slosh back and forth, which will generate tremendous dynamic hydraulic pressure on the tank wall, which in turn will affect the structure In order to study the liquid−solid interaction of the storage tank, Housner [8] first proposed a two-particle mass−spring model, which divided the liquid into a rigid component and a convection component Considering the elastic deformation of the tank wall under load, Haroun and Housne [9] proposed a simplified mechanical model, which takes into account the elastic deformation of the tank wall and the interaction between the liquid and the solid For the convenience of engineering application, Malhotra et al [3] proposed a simplified seismic design method, which takes into account the influence of liquid convection and pulsation

on the tank wall Jadhav et al [10] studied the effect of different isolator parameters on the seismic response of the foundation isolation liquid storage tank In order to verify the correctness of the simplified model of the storage tank proposed by the above researchers, some researchers [11–13] used finite element software to analyze the seismic time history of the storage tank, and compared the calculation results of the finite element and the simpli-fied model; it was found that the difference between the two is not large, which verifies the rationality of the simplified model Moslemi and Kianoush [14] used ANSYS finite element software to conduct a parametric study on the dynamic behavior of cylindrical storage tanks, and the study illustrated that the current liquid tank design codes of the dynamic hydraulic pressure is too conservative Saha et al [15] studied the seismic response of liquid storage tanks isolated by elastomeric bearings and sliding systems under near-fault seismic motion Kangda [16] reviewed the research status of the finite element method used in the barrier and barrier-free liquid storage tanks, and introduced the method of establishing the finite element model of the liquid storage tank in ANSYS software in detail However, as storage tanks are being built larger, it is difficult to control the seismic response of storage tanks with seismic measures

In order to reduce the seismic response of the liquid storage tank, seismic isolation devices are introduced into the liquid storage tank structure, such as friction pendulum bearings, lead-core rubber bearings, etc In order to study the seismic response of the isolated storage tank under the excitation of near-fault ground motion, Panchal et al [17,18] selected different isolation bearings for analysis The research results show that the iso-lating affection of the variable frequency friction pendulum bearing is better than that

of the friction pendulum bearing Zhang et al [19] derived the nonlinear restoring force expression of the multiple friction pendulum system, and studied the seismic response of the isolated storage tank on this basis Tang et al [20] conducted shaking table tests on storage tanks with different isolation devices The test results show that the horizontal dis-placement of the laminated rubber bearing isolated tank is the largest In comparison, both friction pendulum bearing and variable curvature friction pendulum bearing have good isolation over a wider frequency band Moeindarbari et al [21] investigated the multiple level performance of a seismically isolated elevated storage tank isolated with multi−phase friction pendulum bearing, and a mathematical formula involving complex time history analysis was presented for the analysis of a typical storage tank for a multiphase friction pendulum bearing Seleemah et al [22] studied the seismic response of liquid storage tanks isolated by elastomeric or plain bearings; it was found that base isolation is quite effective in reducing the earthquake response of liquid storage tanks The type of site has a significant effect on the seismic response of the storage tank The foundation of the storage tank was considered as a rigid foundation in previous studies In fact, the foundation frequently suffers from uneven settlement Ormeño et al [23] conducted shaking table tests

on rigid-foundation storage tanks and flexible-foundation storage tanks, and the results showed that the axial stress of flexible-foundation storage tanks was reduced compared

to rigid-foundation storage tanks Tsipianitis et al [24] proposed a detailed numerical

Appl Sci 2022, 12, 8390 3 of 20

framework for seismic analysis of liquid storage tanks considering soil-structure interaction (SSI), and studied the effect of SSI on the seismic performance of storage tanks

In summary, the current research has made great progress in the field of seismic resistance (seismic isolation) of storage tanks However, some researchers’ studies are based

on simplified mechanical models or numerical simulation models, without conducting a shaking table test to verify their results A few researchers have carried out shaking table tests, but their studies lack the numerical simulation to prove it In view of this, this paper analyzes the seismic response of the storage tank model based on the shaking table test and numerical simulation, and studies the seismic isolation effect of the lead-core rubber bearing on the storage tank On this basis, the dynamic response of a large LNG storage tank of 200,000 cubic meters under earthquake action is analyzed, and the seismic isolation pattern of the storage tank is studied

2 Shaking Table Test of LNG Storage Tank Model

To reveal the dynamic response mechanism of large-scale LNG storage tanks under earthquake action, a shaking table test was carried out on the structural model of LNG storage tanks in this paper In the experiment, the dynamic response of a storage tank model was obtained by using the acceleration sensor and the displacement sensor, and the dynamic characteristics of a large LNG storage tank were studied

2.1 Test Model This paper takes an actual large-scale LNG storage tank as a reference Considering the complexity of its structure, a simplification was made when designing the structure model storage tank It is necessary to ensure that the prototype structure is similar to the experimental structure during the design, but it is difficult to meet this requirement in most cases Therefore, the storage tank structure model only retains the main structure

of large LNG storage tank, such as the outer tank, pile foundation, dome and inner tank, ignoring the structures that do not bear weight, such as the aluminum ceiling, steel dome and auxiliary pipelines

The geometric dimensions and material parameters of the tank model are as follows The height of the outer tank wall is 2 m, and the sagittal height of the dome is 0.2 m The inner diameter of the outer tank wall is 2.5 m, and the thickness of the outer tank wall

is 0.2 m The distance between the outer tank and the inner tank is 0.35 m, the diameter

of the inner tank is 0.9 m, the height of the inner tank is 1.5 m, and the wall thickness of the inner tank is 5 mm There are 13 pile foundations in the model tank For the seismic storage tank, the pile foundation and the bearing platform of the storage tank are directly connected For the seismic storage tank, lead−core rubber bearings are arranged between the pile foundation and the bearing platform of the storage tank, as shown in Figure1a,b The diameter of the pile is 0.4 m and the length of the pile is 0.3 m The plans of the seismic storage tank and isolation storage tank are shown in Figure1 The outer tank is made

of C50 concrete with an elastic modulus, Poisson’s ratio and density of 34.5 GPa, 0.167 and 2500 kg/m3, respectively The inner tank is made of steel with and elastic modulus, Poisson’s ratio and density of 210 GPa, 0.3 and 7800 kg/m3, respectively

Appl Sci 2022, 12, 8390 4 of 20

Figure 1 The plans of the storage tank: (a) seismic storage tank; (b) isolation storage tank (units:

mm)

The earthquake shaking table is a three-dimensional horizontal excitation hydraulic drive device The specific parameters of this device are as follows: the size of the table is

6 m × 6 m; the maximum load capacity is 60 t; the maximum anti-overturning moment is

1800 kN·m; the limit displacement of the table is ± 250 mm The measurement point layout

of the storage tank model is shown in Figure 1 Acceleration sensors and displacement sensors were arranged in the experiment According to the structural characteristics of the storage tank, acceleration sensors were arranged at the pile foundation, the bearing plat-form, the height of the center of mass, and the dome, and the displacement sensor was arranged at the bottom of the dome Figure 2a is the test model of the storage tank, and Figure 2b is the actual layout of the acceleration sensor The acceleration sensor selected for the test was Endevco 7290E (Endevco Corporation, Irvine, CA, USA); the acceleration range that can be tested was ± 10 g The Endevco 7290E is a rugged, variable capacitance accelerometer with integral electronics for voltage regulation, filtering, and signal ampli-fication

Figure 2 (a) Test model of the storage tank; (b) layout of the acceleration sensor

2900

JSD-1 JSD-2 JSD-3 JSD-4 JSD-5

JSD-6

JSD-7 JSD-8

300

330

390

360

950

100

100

400

200

JSD-9 JSD-10 JSD-11 JSD-12 JSD-13

JSD-14

JSD-15 JSD-16

300

200 390 360 950

100 100

2900

330 400 200

Figure 1 The plans of the storage tank: (a) seismic storage tank; (b) isolation storage tank (units: mm).

The earthquake shaking table is a three-dimensional horizontal excitation hydraulic drive device The specific parameters of this device are as follows: the size of the table is

6 m×6 m; the maximum load capacity is 60 t; the maximum anti-overturning moment is

1800 kN·m; the limit displacement of the table is±250 mm The measurement point layout

of the storage tank model is shown in Figure1 Acceleration sensors and displacement sensors were arranged in the experiment According to the structural characteristics of the storage tank, acceleration sensors were arranged at the pile foundation, the bearing platform, the height of the center of mass, and the dome, and the displacement sensor was arranged at the bottom of the dome Figure2a is the test model of the storage tank, and Figure2b is the actual layout of the acceleration sensor The acceleration sensor selected for the test was Endevco 7290E (Endevco Corporation, Irvine, CA, USA); the acceleration range that can be tested was±10 g The Endevco 7290E is a rugged, variable capacitance accelerometer with integral electronics for voltage regulation, filtering, and signal amplification

Figure 1 The plans of the storage tank: (a) seismic storage tank; (b) isolation storage tank (units:

mm)

The earthquake shaking table is a three-dimensional horizontal excitation hydraulic drive device The specific parameters of this device are as follows: the size of the table is

6 m × 6 m; the maximum load capacity is 60 t; the maximum anti-overturning moment is

1800 kN·m; the limit displacement of the table is ± 250 mm The measurement point layout

of the storage tank model is shown in Figure 1 Acceleration sensors and displacement sensors were arranged in the experiment According to the structural characteristics of the storage tank, acceleration sensors were arranged at the pile foundation, the bearing plat-form, the height of the center of mass, and the dome, and the displacement sensor was arranged at the bottom of the dome Figure 2a is the test model of the storage tank, and Figure 2b is the actual layout of the acceleration sensor The acceleration sensor selected for the test was Endevco 7290E (Endevco Corporation, Irvine, CA, USA); the acceleration range that can be tested was ± 10 g The Endevco 7290E is a rugged, variable capacitance accelerometer with integral electronics for voltage regulation, filtering, and signal ampli-fication

Figure 2 (a) Test model of the storage tank; (b) layout of the acceleration sensor

2900

JSD-1 JSD-2 JSD-3 JSD-4 JSD-5

JSD-6

JSD-7 JSD-8

300

330

390

360

950

100

100

400

200

JSD-9 JSD-10 JSD-11 JSD-12 JSD-13

JSD-14

JSD-15 JSD-16

300

200 390 360 950

100 100

2900

330 400 200

Figure 2 (a) Test model of the storage tank; (b) layout of the acceleration sensor.

2.2 Seismic Wave Selection

In the shaking table test, the ground motion is input in the form of base acceleration

In this paper, the prototype of test tank is located in a Class II site Based on seismic codes

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for building structures [25] and design codes for large oil storage tanks [26], the selected seismic waves should be close to the natural period of the site where the structure is located

to increase the seismic response of the structure Three natural seismic waves and one artificial wave were selected for experiment, namely the El Centro wave, Taft wave, Wolong wave and Artificial wave, which satisfies the wave selection requirements of seismic waves The time history curve of the seismic wave is shown in Figure3 During the experiment, the peak values of seismic wave acceleration were adjusted to 0.1 g, 0.25 g, 0.5 g and 0.75 g, respectively Since the storage tank model is scaled from a large storage tank, the time of the seismic wave needed to be scaled, and the time interval was compressed to 1/5 of the original seismic record The test conditions were carried out according to the peak acceleration from minor to large To determine the changing pattern of the dynamic characteristics of the LNG storage tank, the natural vibration characteristics of the storage tank model were obtained by white noise scanning before the start of the shaking table test and after the application of seismic waves at all levels The arrangement of test conditions

is shown in Table1

2.2 Seismic Wave Selection

In the shaking table test, the ground motion is input in the form of base acceleration

In this paper, the prototype of test tank is located in a Class II site Based on seismic codes for building structures [25] and design codes for large oil storage tanks [26], the selected seismic waves should be close to the natural period of the site where the structure is lo-cated to increase the seismic response of the structure Three natural seismic waves and one artificial wave were selected for experiment, namely the El Centro wave, Taft wave, Wolong wave and Artificial wave, which satisfies the wave selection requirements of seis-mic waves The time history curve of the seisseis-mic wave is shown in Figure 3 During the experiment, the peak values of seismic wave acceleration were adjusted to 0.1 g, 0.25 g, 0.5 g and 0.75 g, respectively Since the storage tank model is scaled from a large storage tank, the time of the seismic wave needed to be scaled, and the time interval was com-pressed to 1/5 of the original seismic record The test conditions were carried out accord-ing to the peak acceleration from minor to large To determine the changaccord-ing pattern of the dynamic characteristics of the LNG storage tank, the natural vibration characteristics of the storage tank model were obtained by white noise scanning before the start of the shak-ing table test and after the application of seismic waves at all levels The arrangement of test conditions is shown in Table 1

Figure 3 Time history of seismic wave acceleration: (a) El Centro wave; (b) Taft wave; (c) Wolong wave; (d) Artificial wave

Table 1 Arrangement of test conditions

Condition

Excitation Direction

Peak Acceleration (g)

Figure 3 Time history of seismic wave acceleration: (a) El Centro wave; (b) Taft wave; (c) Wolong wave; (d) Artificial wave.

Appl Sci 2022, 12, 8390 6 of 20

Table 1.Arrangement of test conditions

Condition Number Test Condition Excitation

Direction

Peak Acceleration (g)

12–21 El Centro, Taft, Wolong, Artificial X; X, Z; X, Y, Z 0.50

23–34 El Centro, Taft, Wolong, Artificial X; X, Z; X, Y, Z 0.75

2.3 Design of Lead-Core Rubber Bearing Using MATLAB software to analyze the frequency spectrum of the seismic wave after compression time, the predominant periods of the El Centro wave, Taft wave, Wolong wave and Artificial wave were 0.125 s, 0.134 s, 0.078 s and 0.067 s, respectively In order to avoid the resonance phenomenon of the test tank, the isolation period should be far from the seismic predominant period A lead-core rubber bearing is arranged between the test tank and the pile foundation, and the parameters of them are shown in Table2

Table 2.Lead-core rubber bearing parameters

effective outer diameter 300 mm shear modulus 0.392 MPa outer diameter of bearing 320 mm rubber standard elastic modulus 1.5 MPa

side length of sealing plate 400 mm effective area 70,685.8 mm2 sealing plate thickness 11 mm bearing area 160,000 mm2 rubber layers 26 layer hardness correction coefficient 0.9 layers of sheet steel 25 layer vertical stiffness 887 kN/mm thickness of rubber layer 3 mm equivalent horizontal stiffness 821 kN/m

total thickness of rubber 78 mm post yield stiffness 469 kN/m total thickness of steel plate 50 mm equivalent damping ratio 30.9%

The calculation formula of the isolation period is as follows [27]:

Tiso=2π

s

Mi+Ms

Total stiffness of horizontal isolation layer Kisois:

Mi = tanh[0.866(D/hw)]

where: Tisois the isolation period; Kisois the horizontal stiffness of the isolation layer; Mi

is the mass of the liquid that moves with the tank; Msis the mass of the tank; kiso is the equivalent stiffness of a single lead-core rubber bearing; D is the diameter of the inner tank;

hwis the height liquid storage, its value is 0.75 m; and Mlis the total mass of the liquid Taking the equivalent stiffness of a single isolation bearing in Table2into Equation (2), and then from Equation (1), the isolation period can be obtained as 0.967 s, which is distant from the predominant period of the input seismic wave This preliminarily indicates that it

is reasonable to choose lead rubber bearing

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3 Analysis of Test Results

3.1 Natural Vibration Characteristics The dynamic characteristics of the tank model will change somewhat after being excited by seismic waves subjected to different peak accelerations By processing the data

in the condition of white noise, the natural vibration frequency of the tank model can be obtained, as shown in Table3

Table 3.Natural vibration frequency of tank model under white noise excitation (Hz)

Condition Number Explanation

Seismic Storage Tank Isolation Storage Tank

6 after 0.10 g

11 after 0.25 g

22 after 0.50 g

35 after 0.75 g

It can be seen from Table3that:

(1) After seismic isolation measures are taken, the natural vibration frequency of the tank model is significantly reduced Before the seismic wave is applied, along the X-direction, the frequencies of the seismic storage tank and the seismic isolation tank are 16.8 Hz and 7.0 Hz After the seismic isolation, the frequency of the storage tank decreases by 9.5 Hz, with a decrease of 56.5% Along the Y-direction, the frequencies

of the seismic storage tank and the isolation storage tank are 16.1 Hz and 7.0 Hz, and the frequency of the storage tank is reduced by 9.1 Hz after isolation, with a decrease

of 56.5% This shows that the isolation bearing has the same effect on the natural vibration frequency of the tank in the X- and Y-directions

(2) With the increase of peak acceleration of the seismic wave, the natural vibration frequency of the seismic storage tank and the seismic isolation storage tank decreases gradually This indicates that the tank was damaged, and that the damage was progressive After the test, along the X-direction, the natural vibration frequencies of the seismic storage tank and the isolation storage tank decreased by 1.8 Hz and 0.9 Hz, respectively; along the Y-direction, the natural vibration frequencies of the seismic storage tank and the isolation storage tank decreased by 2.5 Hz and 1 Hz, respectively This indicates that the damage degree of the isolation storage tank is smaller than that

of the seismic storage tank

3.2 Acceleration Response

In this paper, the data collected under the action of seismic waves with peak accelera-tions of 0.5 g and 0.75 g are selected to analyze acceleration responses and their differences between the seismic storage tank and the isolation storage tank By extracting the peak acceleration of the measurement points, and the results shown in Figures4and5can be obtained As can be seen from the figure:

(1) The acceleration of the seismic storage tank approximately increases linearly along the direction of height, and the acceleration will change abruptly at the dome position, which indicates that the lateral stiffness of the dome position is much lower than that

of the tank wall After the seismic isolation measures are taken, acceleration response

of the storage tank is significantly reduced In the direction of seismic wave action, the isolation effect is particularly obvious Under the action of the Wolong wave (XYZ,

Appl Sci 2022, 12, 8390 8 of 20

0.75 g), the maximum acceleration of the seismic storage tank and the isolation storage tank are 20.68 m/s2and 8.92 m/s2, respectively, and the isolation rate reaches 56.9%

(2) With the increase of peak acceleration of the seismic wave, the acceleration of the seismic storage tank and the isolation storage tank also increases Compared with the Taft wave (XZ direction) condition, when the PGA is 0.50 g, the maximum ac-celerations of the seismic storage tank and the isolation storage tank are 13.62 m/s2 and 2.25 m/s2, respectively; when the PGA is 0.75 g, the maximum accelerations of the seismic storage tank and the isolation storage tank are 17.93 m/s2and 4.21 m/s2, respectively This is because of the arrangement of lead-core rubber bearings in the isolation tank, so the increase of the acceleration of the isolation storage tank is not as obvious as that of the seismic tank

(2) With the increase of peak acceleration of the seismic wave, the acceleration of the seismic storage tank and the isolation storage tank also increases Compared with the Taft wave (XZ direction) condition, when the PGA is 0.50 g, the maximum accelera-tions of the seismic storage tank and the isolation storage tank are 13.62 m/s2 and 2.25

storage tank and the isolation storage tank are 17.93 m/s2 and 4.21 m/s2, respectively This is because of the arrangement of lead-core rubber bearings in the isolation tank,

so the increase of the acceleration of the isolation storage tank is not as obvious as that of the seismic tank

Figure 4 Comparison of peak acceleration in the X-direction of the seismic storage tank: (a) Taft wave (XZ direction, 0.50 g); (b) Artificial wave (XYZ direction, 0.50 g); (c) Wolong wave (XYZ direc-tion, 0.75 g); (d) Taft wave (XZ direcdirec-tion, 0.75 g)

Figure 4 Comparison of peak acceleration in the X-direction of the seismic storage tank: (a) Taft wave (XZ direction, 0.50 g); (b) Artificial wave (XYZ direction, 0.50 g); (c) Wolong wave (XYZ direction, 0.75 g); (d) Taft wave (XZ direction, 0.75 g).

The above only compares the peak accelerations of the seismic and the isolation storage tanks In order to visualize how their acceleration changes, the acceleration time history curves of measuring point 5 and measuring point 17 are selected for comparative analysis in the time domain and frequency domain Figures6and7are the acceleration time history curve and the corresponding spectrum curve under the action of the Taft wave (XYZ direction, 0.75 g) and the Wolong wave (XYZ direction, 0.75 g), respectively It can be seen from the comparison of acceleration time history curves that the acceleration response

of the isolation storage tank is smaller than that of the seismic storage tank, which indicates that the lead-core rubber bearing has a good seismic isolation effect Comparing Figure6

with Figures6c and 7a,c, it is also found that the seismic isolation effect of lead-core rubber bearing is related to the seismic wave Under the action of the Wolong wave (XYZ direction, 0.75 g), the isolation efficiency of lead-core rubber bearing is 74.8% (X-direction)

Appl Sci 2022, 12, 8390 9 of 20

and 68.0% (Y-direction), respectively; under the action of the Taft wave (XYZ direction, 0.75 g), the isolation efficiency of the lead-core rubber bearing is 33.2% (X-direction) and 48.5% (Y-direction), respectively

Figure 5 Comparison of peak acceleration in the X direction of the isolation storage tank: (a) Taft

wave (XZ direction, 0.50 g); (b) Artificial wave (XYZ direction, 0.50 g); (c) Wolong wave (XYZ direc-tion, 0.75 g); (d) Taft wave (XZ direcdirec-tion, 0.75 g)

The above only compares the peak accelerations of the seismic and the isolation stor-age tanks In order to visualize how their acceleration changes, the acceleration time his-tory curves of measuring point 5 and measuring point 17 are selected for comparative analysis in the time domain and frequency domain Figures 6 and 7 are the acceleration time history curve and the corresponding spectrum curve under the action of the Taft wave (XYZ direction, 0.75 g) and the Wolong wave (XYZ direction, 0.75 g), respectively

It can be seen from the comparison of acceleration time history curves that the acceleration response of the isolation storage tank is smaller than that of the seismic storage tank, which indicates that the lead-core rubber bearing has a good seismic isolation effect Com-paring Figure 6a with Figures 6c and 7a,c, it is also found that the seismic isolation effect

of lead-core rubber bearing is related to the seismic wave Under the action of the Wolong wave (XYZ direction, 0.75 g), the isolation efficiency of lead-core rubber bearing is 74.8% (X-direction) and 68.0% (Y-direction), respectively; under the action of the Taft wave (XYZ direction, 0.75 g), the isolation efficiency of the lead-core rubber bearing is 33.2% (X-direc-tion) and 48.5% (Y-direc(X-direc-tion), respectively

Figure 5 Comparison of peak acceleration in the X direction of the isolation storage tank: (a) Taft wave (XZ direction, 0.50 g); (b) Artificial wave (XYZ direction, 0.50 g); (c) Wolong wave (XYZ direction, 0.75 g); (d) Taft wave (XZ direction, 0.75 g).

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Figure 6 Taft wave (XYZ direction, 0.75 g): (a) acceleration time history curves in the X-direction; (b) spectrum characteristic curve in the X-direction; (c) acceleration time history curves in the Y-direction; (d) spectrum characteristic curve in the Y-direction

Comparing spectral characteristics of the acceleration response, it can be seen that the spectral curve of the seismic storage tank has two obvious peaks, while the spectral characteristic curve of the isolation storage tank has only one peak Under the action of the Taft wave (XYZ direction, 0.75 g), the two peaks of the seismic storage tank are located around 13 Hz and 32 Hz, respectively, and the peak value of the isolation tank is located around 6 Hz Under the action of the Wolong wave (XYZ direction, 0.75 g), the two peaks

of the seismic storage tank are located around 10 Hz and 35 Hz, respectively, and the peak value of the isolation tank is located around 7 Hz This shows that the lead-core rubber bearing can significantly suppress the high-frequency components in seismic waves

Figure 6 Taft wave (XYZ direction, 0.75 g): (a) acceleration time history curves in the X-direction; (b) spectrum characteristic curve in the X-direction; (c) acceleration time history curves in the Y-direction; (d) spectrum characteristic curve in the Y-direction.

Figure 7 Wolong wave (XYZ direction, 0.75 g): (a) acceleration time history curves in the X-direc-tion; (b) spectrum characteristic curve in the X-direcX-direc-tion; (c) acceleration time history curves in the Y-direction; (d) spectrum characteristic curve in the Y-direction

3.3 Numerical Simulation of Experimental Tank Model

ANSYS software was used to simulate the experimental storage tank model, and the differences between the numerical results and the experimental results are compared to verify the validity and reliability of the finite element model, paving the way for further study on seismic performance of large LNG storage tanks The bilinear kinematic harden-ing model was used for the concrete outer tank, dome and pile foundation The material parameters of the numerical model are based on those of the test tank, and the parameters

of the lead-core rubber bearing are shown in Table 2 The storage tank is simulated by the SOLID186 element The pile foundation is simulated by the BEAM188 element The con-tact element is used for connection between the pile foundation and the storage tank Zhang et al [12,28–30] have conducted in-depth research on the numerical simulation of LNG storage tanks Their article gives detailed information about the meshing method and mesh element selection The results show that by dividing two elements along the thickness direction and ensuring that the element shape is a cube as much as possible, the simulated results can have high computational accuracy Therefore, the finite element model of the LNG storage tank in this paper was divided into 2 elements in the thickness direction, 64 elements in the hoop direction, and 21 elements in the height direction; the mapped meshing method was used for the mesh division The selected element is SOLID186 element, which is a high-order element with 20 nodes and three degrees of freedom, with a total of 10,169 elements

In the element library of ANSYS, there is no element that can directly simulate the mechanical properties of lead-core rubber isolation bearings Therefore, it is necessary to simplify the mechanical properties of the isolation bearing and conduct a reasonable sim-ulation according to mechanical behavior of the isolation bearing The lead-core rubber bearing has good hysteresis performance and can be simulated by a bilinear model The mechanical properties of the lead-core rubber bearing in the horizontal and vertical direc-tions are very different The lead-core rubber bearing will yield in the horizontal direction,

Figure 7 Wolong wave (XYZ direction, 0.75 g): (a) acceleration time history curves in the X-direction; (b) spectrum characteristic curve in the X-direction; (c) acceleration time history curves in the Y-direction; (d) spectrum characteristic curve in the Y-direction.

Comparing spectral characteristics of the acceleration response, it can be seen that the spectral curve of the seismic storage tank has two obvious peaks, while the spectral