scholarly journals The seismic response of elevated liquid storage tanks isolated by lead-rubber bearings

2003 ◽  
Vol 36 (3) ◽  
pp. 141-164 ◽  
Author(s):  
M.K. Shrimali ◽  
R.S. Jangid
Keyword(s):  
Seismic Response ◽  
Seismic Isolation ◽  
Degree Of Freedom ◽  
Earthquake Ground Motion ◽  
Storage Tanks ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Liquid Storage ◽  
Tower Structure ◽  
Lumped Masses

The seismic response of elevated liquid storage tanks isolated by the lead-rubber bearing is investigated under real earthquake ground motion. Two types of isolated tank models are considered in which the bearings are placed at the base and top of the tower structure. The tank liquid is modelled as lumped masses referred as convective mass, impulsive mass and rigid mass. The corresponding stiffness associated with these lumped masses has been worked out using the properties of the tank wall and liquid mass based on simple single-degree-of-freedom concepts. The mass of the tower structure is lumped equally at top and bottom. The assembled equations of motion are solved by Newmark's step-by-step method with iteration. The seismic response of two types of tanks, namely slender and broad tanks is obtained and a parametric study is carried out to study the effects of important system parameters on the effectiveness of seismic isolation. The various important parameters considered are the tank aspect ratio, the time period of the tower structure, damping and the lime period of the isolation system. It has been observed that the earthquake response of the isolated tank is reduced significantly. Further, it is observed that the isolation is more effective for the tank with a stiff tower structure in comparison to flexible towers. In addition, a simplified analysis is also presented to evaluate the response of the elevated tanks using a two-degrees-of-freedom model and two single degree-of-freedom models. It is observed that the proposed methods predict accurately the seismic response of elevated liquid storage tanks with less computational efforts.

Dynamic Analysis of Liquid Storage Tanks with Sliding Systems

2003 ◽  
Vol 6 (2) ◽  
pp. 145-158 ◽  
Author(s):  
M. K. Shrimali ◽  
R. S. Jangid
Keyword(s):  
Seismic Response ◽  
Frictional Force ◽  
Seismic Isolation ◽  
Earthquake Ground Motion ◽  
Hysteretic Model ◽  
Storage Tanks ◽  
Step Method ◽  
Conventional Model ◽  
Liquid Mass ◽  
Liquid Storage

Dynamic response of liquid storage tanks isolated by the sliding systems is investigated under real earthquake ground motion. The frictional force of sliding systems is modelled by conventional and hysteretic models. The continuous liquid mass is lumped as convective mass, impulsive mass and rigid mass. The corresponding stiffness associated with these lumped masses is worked out depending upon the properties of the tank wall and liquid mass. The governing equations of motion of the tank with sliding system are derived and solved by Newmark's step-by-step method with iterations. The frictional force mobilized at the interface of the sliding system is assumed to be velocity dependent. For comparative study, the seismic response of isolated liquid storage tank obtained by the conventional model is compared with the corresponding response obtained by the hysteretic model. In order to measure the effectiveness of isolation system, the seismic response of isolated tank is compared with that of the non-isolated tank. A parametric study is also conducted to study the effects of aspect ratio of tank on the effectiveness of seismic isolation of liquid storage tanks. It is found that the sliding systems are quite effective in reducing the earthquake response of liquid storage tanks. In addition, the conventional and the hysteretic model of the sliding system predict the same seismic response of liquid storage tanks. However, the conventional model is relatively more computationally efficient as compared to the hysteretic model.

scholarly journals Response of Base-Isolated Liquid Storage Tanks

2004 ◽  
Vol 11 (1) ◽  
pp. 33-45 ◽  
Author(s):  
M.B. Jadhav ◽  
R.S. Jangid
Keyword(s):  
Seismic Response ◽  
Seismic Isolation ◽  
Equations Of Motion ◽  
Approximate Model ◽  
Storage Tanks ◽  
Step Method ◽  
Earthquake Excitation ◽  
System Parameters ◽  
Liquid Storage ◽  
Isolation Systems

Seismic response of liquid storage tanks isolated by elastomeric bearings and sliding system is investigated under real earthquake ground motions. The continuous liquid mass of the tank is modeled as lumped masses known as sloshing mass, impulsive mass and rigid mass. The coupled differential equations of motion of the system are derived and solved in the incremental form using Newmark's step-by-step method with iterations. The seismic response of isolated tank is studied to investigate the comparative effectiveness of various isolation systems. A parametric study is also carried out to study the effect of important system parameters on the effectiveness of seismic isolation for liquid storage tanks. The various important parameters considered are: (i) aspect ratio of the tank and (ii) the time period of the isolation systems. It was observed that both elastomeric and sliding systems are found to be effective in reducing the earthquake forces of the liquid storage tanks. However, the elastomeric bearing with lead core is found to perform better in comparison to other systems. Further, an approximate model is proposed for evaluation of seismic response of base-isolated liquid storage tanks. A comparison of the seismic response evaluated by the proposed approximate method and an exact approach is made under different isolation systems and system parameters. It was observed that the proposed approximate analysis provides satisfactory response estimates of the base-isolated liquid storage tanks under earthquake excitation.

Seismic Response Reduction Caused by Coupling Between Beam-Type and Oval-Type Vibrations of a Cylindrical Water Storage Tank Under Large Excitation

2007 ◽  
Author(s):  
Akira Maekawa ◽  
Katsuhisa Fujita ◽  
Michiaki Suzuki
Keyword(s):  
Seismic Response ◽  
Water Storage ◽  
Degree Of Freedom ◽  
Seismic Excitation ◽  
System Model ◽  
Single Degree Of Freedom ◽  
Water Storage Tank ◽  
Single Degree ◽  
Input Acceleration ◽  
Beam Type

This study describes the response reduction caused by coupling between the beam-type and the oval-type vibrations of a cylindrical water storage tank under seismic excitation. In this study, the seismic response experiment is performed by using a 1/10 reduced scale model of an actual tank and then numerical simulation is performed by the simplified model. The authors conducted the sinusoidal response experiment for the tank and reported that the coupling between the beam-type and the oval-type vibrations causes the resonance frequency of the beam-type vibration to shift to the lower frequency and the response in the beam-type vibration (the response of the tank) to reduce. The seismic response experiment of the tank model filled with water up to 95% is performed by a shaking table. The El Centro 1940 NS and the improved standard seismic wave for Japanese LWR are used as the input seismic wave. The experimental results show that the maximum response acceleration does not enlarge linearly as the maximum input acceleration increases. The dominant resonance frequency slightly shifts to the lower frequency as the maximum input acceleration increases. It is concluded that the coupling between the beam-type and the oval-type vibrations make an influence on the beam-type vibration in seismic excitation. In the meantime, the authors propose the nonlinear single-degree-of-freedom system model to explain that the vibration response of the tank reduces. This model is based on geometric nonlinearity due to the out-of-plane deformation of the side-wall of the tank caused by the oval-type vibration. The numerical simulation of the seismic response is conducted using the nonlinear single-degree-of-freedom system model proposed by the authors. The analytical results agree with the experimental results as a general trend. Therefore, it is concluded that the response reduction of the tank is generated by coupling between the beam-type and the oval-type vibrations in the seismic excitation as well as the sinusoidal excitation. In addition, the response reduction rate of the tank under much larger seismic excitation can be estimated by using the nonlinear single-degree-of-freedom system model.

scholarly journals Observation of a directed resonance in soil driven by transverse rock motion

1989 ◽  
Vol 22 (2) ◽  
pp. 81-89 ◽  
Author(s):  
W. R. Stephenson
Keyword(s):  
Seismic Response ◽  
Resonant Mode ◽  
Degree Of Freedom ◽  
Mechanical Oscillator ◽  
Ground Acceleration ◽  
Single Degree Of Freedom ◽  
Fine Grained ◽  
Single Degree ◽  
Cook Strait

One component of horizontal ground acceleration recorded on flexible soil during the 1968 November 1 Cook strait earthquake is shown to be well modelled as a single degree of freedom oscillator excited by the recorded component of transverse acceleration in nearby bed rock. This is shown to be consistent with the cellular resonant mode hypothesis of seismic response of flexible soil. The mechanical oscillator is identified as a layer of fine-grained, post-glacial alluvium of approximately 20 m thickness.

A Simplified Analysis Method for Elasto-Plastic Seismic Response Using the Energy Balance Equation of a Maximum Hysteresis Loop

2015 ◽  
Author(s):  
Gaku Nakamura ◽  
Yukihiko Okuda ◽  
Shoichi Ebato ◽  
Hiroshi Niwa ◽  
Tadashi Iijima ◽  
...  
Keyword(s):  
Energy Balance ◽  
Seismic Response ◽  
Degree Of Freedom ◽  
Integration Scheme ◽  
Analysis Method ◽  
Maximum Displacement ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Simplified Analysis ◽  
Vibration Tests

With increasing magnitude of design earthquake ground motions, it is necessary to develop methods of evaluating the seismic safety margin that are more exact than the current methods. However, a standard nonlinear analysis method requires step by step calculations of the numerical time integration scheme to obtain the seismic response. The authors present a new simplified analysis method of elasto-plastic seismic response. The proposed method is formulated by the energy balance between the input energy and the dissipated energy of an equivalent single degree of freedom model for actual equipment. Assuming the harmonic resonance of the single degree of freedom model, the maximum displacement response can be estimated conservatively. To verify the proposed method, static tests and vibration tests with cantilever-type specimens were performed. The vibration tests were conducted with sine, sweep down sine and random waves to verify the conservativeness of the proposed method. Comparisons of the maximum displacement between the tests and the proposed method show the conservative estimation of the displacement by the proposed method.

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