Dynamic Buckling Test of Modified 1/10 Scale Model of Cylindrical Water Storage Tank

2007 ◽  
Author(s):  
Akira Maekawa ◽  
Katsuhisa Fujita ◽  
Toru Sasaki
Keyword(s):  
Fluid Pressure ◽  
Water Storage ◽  
Initial Imperfection ◽  
Buckling Analysis ◽  
Dynamic Buckling ◽  
Scale Model ◽  
The Finite Element Method ◽  
Tank Model ◽  
Water Storage Tank ◽  
Reduced Scale

This study reports on the dynamic buckling experiment of a 1/10 reduced scale model of a large-scale cylindrical water storage tank by using a shaking table, and the buckling analysis by using both the simplified method and the finite element method. The dynamic buckling experiment is performed by using the reduced scale tank model whose initial imperfection has been measured. The tank model is filled with water up to 95% of the full level, and puts 200-weight on its top, overcoming the response reduction induced by the oval-type vibration. The sinusoidal waves are used as the input. As a result of the experiment, the bucking occurs on the tank and plastic deformation is observed on the side and bottom of the tank. Two methods of the buckling analysis are carried out. At first, the buckling load is estimated by using a simplified method adopted in the current Japanese guideline. The analytical result shows this method is conservative despite using the tank with initial imperfection. Secondly, the static buckling analysis with the finite element method is conducted. There is an issue how to treat the dynamic fluid pressure distribution of the contained water in the tank with regard to the static analysis, because the coupling between fluid and structure cannot be taken into consideration. In this study, the distribution of the dynamic fluid pressure is calculated in accordance with the Fischer’s method. The buckling load calculated by using the dynamic fluid pressure distribution agrees with that of the experiment approximately. Therefore, it is appropriate to apply this proposed static analytical method to seismic design.

Nonlinear Vibration Response of a Cylindrical Water Storage Tank Caused by Coupling Effect Between Beam-Type Vibration and Oval-Type Vibration: Part 1 — Vibration Experiment

2006 ◽  
Author(s):  
Akira Maekawa ◽  
Michiaki Suzuki ◽  
Katsuhisa Fujita
Keyword(s):  
Nonlinear Vibration ◽  
Storage Tank ◽  
Coupling Effect ◽  
Water Storage ◽  
Scale Model ◽  
Water Storage Tank ◽  
Vibration Experiment ◽  
Input Acceleration ◽  
Beam Type ◽  
Reduced Scale

In this study, a vibration experiment with a reduced scale model of a large-size cylindrical water storage tank has been performed in order to investigate the nonlinear vibration responses of the cylindrical tank when the beam-type vibration and the oval-type vibration are coupled. In the vibration experiment, a sinusoidal sweep test was performed by using a shaking table on the reduced scale model of the cylindrical water storage tank filled with water to the 95% level. The test was conducted by varying the input acceleration from smaller to larger input in several steps to identify the vibration modes and evaluate the vibration behaviors of the beam-type vibration and the oval-type vibration. As a result, the resonance curves showed that the resonance frequency shifted to the lower frequency region and the response magnification factor became smaller when the input acceleration level became higher. When the magnitude of the input acceleration increased furthermore, the resonance curves were changed to be duller from the sharp peak and the resonance points became unclear. The measured displacements and strains of the sidewall of the model tank showed that the oval-type vibration was excited in the vicinity of the beam-type resonance frequency and that the amplitude of the oval-type vibration increased too significant to be ignored when larger input was applied. It was verified that the oval-type vibration with a subharmonic resonance of order one-half was excited when larger input was applied. This phenomenon was not observed when small input was applied. This shows that the vibration behaviors caused by coupling effect between beam-type vibration and oval-type vibration depend on the magnitude of input excitation. From these results, it can be assumed that the oval-type vibration is closely related to the nonlinear vibration response phenomena of a cylindrical water storage tank.

Vibration Test of 1/10 Scale Model of Cylindrical Water Storage Tank

2004 ◽  
Author(s):  
Akira Maekawa ◽  
Yasutaka Shimizu ◽  
Michiaki Suzuki ◽  
Katsuhisa Fujita
Keyword(s):  
Storage Tank ◽  
Large Scale ◽  
Seismic Waves ◽  
Fluid Pressure ◽  
Water Storage ◽  
Seismic Excitation ◽  
Scale Model ◽  
Vibration Test ◽  
Water Storage Tank ◽  
Circumferential Distribution

Large-scale cylindrical water storage tanks have a large ratio of radius to thickness, which means their thickness is relatively thin compared with the radius. Regarding seismic responses, the deformation of a tank frame is significantly influenced by the sloshing of the water inside the tank and by the bulging vibration of the tank structure, therefore it is important to consider such deformation theoretically and experimentally. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale industrial cylindrical water storage tank, conducted particularly to clarify the dynamic behavior of the tank during a seismic excitation. First a sinusoidal wave excitation experiment was performed for the scale model tank, which measured axial distributions of dynamic fluid pressures, strains and accelerations. Ovaling vibration of the scale model tank also was examined by measuring the circumferential distribution of strains. Furthermore, the dependence of dynamic fluid pressure on the acceleration magnitude of the input excitation was investigated. Secondly, a seismic excitation experiment was conducted using typical seismic waves. Finally, the measuring results were compared with the values calculated using common seismic-proof design methods based on the Housner method or velocity potential theory and the finite element method. Considering the differences between the experiment values and numerical design ones, it became obvious that there was inconsistent between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure was dependent on the acceleration magnitude. And it was suggested that such phenomena were caused by ovaling vibration. They, however, had little effect on the seismic-proof design of the tank in the range of acceleration used in this study.

Vibration Test of a 1/10 Reduced Scale Model of Cylindrical Water Storage Tank

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Akira Maekawa ◽  
Yasutaka Shimizu ◽  
Michiaki Suzuki ◽  
Katsuhisa Fujita
Keyword(s):  
Seismic Design ◽  
Fluid Pressure ◽  
Water Storage ◽  
Seismic Excitation ◽  
Scale Model ◽  
Seismic Load ◽  
Storage Tanks ◽  
Distribution Shape ◽  
Vibration Tests ◽  
Reduced Scale

This paper describes the results of vibration tests using a 1/10 reduced scale model of large-scale cylindrical water storage tanks to clarify their dynamic behavior under seismic excitation. The thin sidewall of the tanks is not so rigid that the vibration modes (sloshing and bulging) induced by earthquake can affect the distribution of their liquid pressure and seismic load. It is, therefore, important for the seismic design of water storage tanks to consider such elastic deformation theoretically and experimentally. In this study, vibration tests by shaking table are conducted using a reduced scale tank model partially filled with water to investigate the dynamic fluid pressure behavior and seismic-proof safety of the tanks. A small sinusoidal excitation test, large amplitude sinusoidal excitation test and seismic excitation test are conducted. The measured values are compared with the calculated ones by some conventional seismic design methods. The results reveal that the distribution shape and magnitude of the dynamic fluid pressure are different between under positive and negative pressures and depend on the magnitude of input acceleration. Further examination concludes that the oval-type vibration, which is a high-order vibration mode, occurring on the sidewall of the tanks affects the distribution shape and magnitude of dynamic fluid pressure. However, it is demonstrated that the vibration does not act as a seismic load in the conventional evaluation of seismic-proof safety.

Dynamic Buckling Analysis of Cylindrical Water Storage Tanks: A New Simulation Method Considering Coupled Vibration Between Fluid and Structure

2009 ◽  
Author(s):  
Akira Maekawa ◽  
Katsuhisa Fujita
Keyword(s):  
Shell Structure ◽  
Water Storage ◽  
Safety Margin ◽  
Time History ◽  
Buckling Analysis ◽  
Dynamic Buckling ◽  
Coupled Analysis ◽  
Storage Tanks ◽  
Analysis Method ◽  
Coupled Vibrations

This paper proposes a dynamic buckling analysis method which can accurately simulate the buckling behavior of cylindrical water storage tanks during an earthquake. The proposed method takes into account the behavior of oval-type vibration as well as beam-type vibration, which are coupled vibrations between the shell structure of the tank and the water stored in the tank. In the proposed method, both the tank and the stored water are three-dimensionally modeled by finite elements and time history analysis is conducted. Moreover, coupled analysis between the fluid and structure and large deformation analysis to the shell structure of the tank are also considered. The analytical results by the proposed method agreed well with those of experiments regarding occurrence of oval-type vibration, mode of buckling and buckling load. The method can accurately simulate the seismic response including the coupled vibrations and the process of damage such as buckling of the cylindrical water storage tank during an earthquake. In conclusion, the proposed dynamic buckling analysis method can quantitatively evaluate the seismic performance of water storage tanks such as seismic safety margin.

Study of Correlation Between Beam Vibration and Oval Vibration on Cylindrical Water Storage Tank

2005 ◽  
Author(s):  
Akira Maekawa ◽  
Yasutaka Shimizu ◽  
Michiaki Suzuki ◽  
Katsuhisa Fujita
Keyword(s):  
Natural Frequency ◽  
Large Amplitude ◽  
Storage Tank ◽  
Excitation Frequency ◽  
Water Storage ◽  
Scale Model ◽  
Vibration Test ◽  
Large Radius ◽  
Water Storage Tank ◽  
Test Tank

A large cylindrical water storage tank, widely used at power stations and chemical plants, typically has a large radius/wall-thickness ratio. The relatively thin sidewall of such a tank can deform easily during an earthquake due to vibrations of the tank structure. In order to improve the seismic-proof design practices for a water storage tank of flexible structure and to develop a new seismic resistance evaluation method to be adopted in future, it is important to understand the dynamic responses of such a tank to seismic motions including the nonlinearity of responses to large amplitude vibrations. This paper reports on the results of vibration test, in which sinusoidal wave excitations with large amplitude were conduced to the scale model tank of a thin-walled cylindrical water storage tank, and the theoretical analysis of the dynamics of the vibratory behaviors that were observed during the vibration test. First, a frequency sweep test was performed over the range that covered the natural frequency. The response of the test tank as a whole to given vibrations remained almost the same over the excitation frequency range. Frequency analysis of the response of the tank failed to locate any resonance points at or around frequencies that had been determined by the basic vibration characteristic test that we had conducted in advance. Next, a large amplitude excitation tests were carried out, in which the test tank was excited intensively by several tens of sinusoidal waves of a fixed frequency that was in the vicinity of the resonant frequency. The response of the tank as a whole in the form of beam vibrations did not intensify in proportion to the input acceleration; it did not go beyond a certain level. Since both of the tests produced significant oval vibrations on the sidewall of tank, the influence of oval vibrations over beam vibrations was analyzed. The analysis concerning the deflection of the sidewall of tank by the additional appearance of oval vibrations in the presence of beam vibrations revealed that a major decrease in the flexural rigidity reduced the response (beam vibrations) of the whole tank. The phenomenon was modeled using a nonlinear equation of motion, assumed that the rigidity depended on the amplitude of oval vibrations. The analysis using this equation explained the results of the above-mentioned tests very well. Thus, it was demonstrated both empirically and analytically that beam vibrations of a cylindrical water storage tank are reduced by the appearance of oval vibrations that have the effect of lowering the natural frequency.

Experimental Study of Coupling Vibration Characteristics Between a Thin Cylindrical Water Storage Tank and Its Contained Liquid

2005 ◽  
Author(s):  
Akira Maekawa ◽  
Yasutaka Shimizu ◽  
Michiaki Suzuki ◽  
Katsuhisa Fujita
Keyword(s):  
Storage Tank ◽  
Excitation Frequency ◽  
Fluid Pressure ◽  
Water Storage ◽  
Fem Analysis ◽  
Shaking Table ◽  
Vibration Modes ◽  
Coupled Vibration ◽  
Fluid Structure ◽  
Water Storage Tank

A large cylindrical water storage tank typically has a thin sidewall. When such a tank is under an earthquake, the vibrations of the water inside are coupled with the vibrations of the sidewall, producing a phenomenon called fluid-structure coupled vibration. The fluid-structure coupled vibration is an important issue for a tank like this to achieve reasonable seismic-proof design. Even though there have been many studies on fluid-structure coupled vibrations, only a few of them have examined the dynamic fluid pressure and oval vibrations. This paper reports on the investigations into the characteristics of oval vibrations exhibited by a cylindrical water storage tank, in which a vibration test was conducted using a shaking table, the correlation of changes in the excitation force and behaviors of dynamic fluid pressure with the appearance and growth of oval vibrations were analyzed, and the modes of oval vibrations that appeared were identified. The vibration test was conducted using a scale model tank of a large cylindrical water storage tank and a shaking table. The input vibrations were sinusoidal waves of 53 Hz, a frequency that was in the vicinity of the resonance frequency. The test took the form of a large amplitude excitation test, which increased the acceleration of the input vibrations gradually. The response acceleration of the tank and the dynamic fluid pressure were measured. Strain gages attached around the trunk of the tank were used to identify oval vibration modes. The frequency analysis of the dynamic fluid pressure revealed two major peaks, one at 53 Hz which matched the excitation frequency and the other at 106 Hz which was double the excitation frequency. It showed that the dynamic fluid pressure has nonlinear behavior like higher-harmonic resonance. The frequency analysis of the responses on the trunk of the tank arising from oval vibrations also revealed two major peaks, one at 53Hz and the other at 106Hz. The behavior of dynamic fluid pressure and the behavior of oval vibrations were coupled. It was found that a certain magnitude of the response acceleration of the tank that gave rise to oval vibrations were in proportion to the rate of increase of the response acceleration of the tank. In other words, oval vibrations appeared at a relatively low response acceleration if the response acceleration increased slowly, whereas oval vibrations appeared only at a relatively high response acceleration if the response acceleration increased quickly. An analysis of the circumferential distribution of circumferential strains around the trunk of the tank revealed the presence of two oval vibration modes with different circumferential wave numbers: 14 and 16, which have not been predicted by the FEM analysis. None of the natural frequencies determined by the FEM analysis of the two different vibration modes matched 106 Hz; however, a half of the sum of the two natural frequencies was close to 106 Hz. Thus oval vibrations were found to have a nonlinear characteristics experimentally.

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