scholarly journals Dynamic Instability of Pile-Supported Structures in Liquefiable Soils during Earthquakes

2008 ◽  
Vol 15 (6) ◽  
pp. 665-685 ◽  
Author(s):  
S. Adhikari ◽  
S. Bhattacharya
Keyword(s):  
Natural Frequency ◽  
Dynamic Instability ◽  
Tall Buildings ◽  
Experimental System ◽  
Oil Platforms ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Piled Structure ◽  
Slender Columns ◽  
Tip Mass

Piles are long slender columns installed deep into the ground to support heavy structures such as oil platforms, bridges, and tall buildings where the ground is not strong enough to support the structure on its own. In seismic prone zones, in the areas of soft soils (loose to medium dense soil which liquefies like a quick sand) piles are routinely used to support structures (buildings/ bridges). The pile and the building vibrate, and often collapse, in liquefiable soils during major earthquakes. In this paper an experimental and analytical approach is taken to characterize this vibration. The emphasis has been given to the dynamic instability of piled foundations in liquefied soil. The first natural frequency of a piled-structure vibrating in liquefiable soil is obtained from centrifuge tests. The experimental system is modelled using a fixed-free Euler-Bernoulli beam resting against an elastic support with axial load and tip mass with rotary inertia. Natural frequencies obtained from the analytical method are compared with experimental results. It was observed that the effective natural frequency of the system can reduce significantly during an earthquake.

scholarly journals Sustainable Measures for Protection of Structures Against Earthquake Induced Liquefaction

2021 ◽  
Author(s):  
Gopal S. P. Madabhushi ◽  
Samy Garcia-Torres
Keyword(s):  
Soil Liquefaction ◽  
Excess Pore Pressure ◽  
Economic Losses ◽  
Element Analysis ◽  
Centrifuge Testing ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Recent Earthquakes ◽  
Excess Pore Pressures ◽  
Excess Pore

AbstractSoil liquefaction can cause excessive damage to structures as witnessed in many recent earthquakes. The damage to small/medium-sized buildings can lead to excessive death toll and economic losses due to the sheer number of such buildings. Economic and sustainable methods to mitigate liquefaction damage to such buildings are therefore required. In this paper, the use of rubble brick as a material to construct earthquake drains is proposed. The efficacy of these drains to mitigate liquefaction effects was investigated, for the first time to include the effects of the foundations of a structure by using dynamic centrifuge testing. It will be shown that performance of the foundation in terms of its settlement was improved by the rubble brick drains by directly comparing them to the foundation on unimproved, liquefiable ground. The dynamic response in terms of horizontal accelerations and rotations will be compared. The dynamic centrifuge tests also yielded valuable information with regard to the excess pore pressure variation below the foundations both spatially and temporally. Differences of excess pore pressures between the improved and unimproved ground will be compared. Finally, a simplified 3D finite element analysis will be introduced that will be shown to satisfactorily capture the settlement characteristics of the foundation located on liquefiable soil with earthquake drains.

Centrifuge Modeling on Seismic Behavior of Pile in Liquefiable Soil Ground

2013 ◽  
Vol 479-480 ◽  
pp. 1139-1143
Author(s):  
Wen Yi Hung ◽  
Chung Jung Lee ◽  
Wen Ya Chung ◽  
Chen Hui Tsai ◽  
Ting Chen ◽  
...  
Keyword(s):  
Seismic Behavior ◽  
Soil Structure ◽  
Lateral Displacement ◽  
Bending Moment ◽  
Soil Liquefaction ◽  
Centrifuge Modeling ◽  
Shaking Table ◽  
Pile Head ◽  
Liquefiable Soil ◽  
Tip Mass

Dramatic failure of pile foundations caused by the soil liquefaction was founded leading to many studies for investigating the seismic behavior of pile. The failures were often accompanied with settlement, lateral displacement and tilting of superstructures. Therefore soil-structure interaction effects must be properly considered in the pile design. Two tests by using the centrifuge shaking table were conducted at an acceleration field of 80 g to investigate the seismic response of piles attached with different tip mass and embedded in liquefied or non-liquefied deposits during shaking. It was found that the maximum bending moment of pile occurs at the depth of 4 m and 5 m for dry sand and saturated sand models, respectively. The more tip mass leads to the more lateral displacement of pile head and the more residual bending moment.

Design of a Vibration-Based Energy Harvester With Adjustable Natural Frequency

2010 ◽  
Author(s):  
Mohamed O. Mansour ◽  
Mustafa H. Arafa ◽  
Said M. Megahed
Keyword(s):  
Energy Harvesting ◽  
Natural Frequency ◽  
Piezoelectric Layer ◽  
System Performance ◽  
Energy Harvester ◽  
Natural Frequencies ◽  
Opposite Polarity ◽  
Energy Harvesters ◽  
Close Proximity ◽  
Tip Mass

The recent years have witnessed a wealth of research on energy harvesting technologies. To maximize the output power, vibration-based energy harvesters are normally designed to have natural frequencies that match those of the excitation. This has spurred interest into the design of devices that possess tunable natural frequencies to cope with sources which exhibit varying frequencies. In this work, an energy harvester is proposed in the form of a base excited cantilever treated with a piezoelectric layer. The cantilever carries a tip mass in the form of a magnet which is placed in close proximity to another magnet with opposite polarity. Different values of axial tensions, and hence different natural frequencies, are obtained by adjusting the gap between the magnets. A dynamic model to predict the system performance is presented and verified experimentally. Based on the findings of this paper, natural frequencies ranging from 3.19–12 Hz were achieved.

Natural frequency coalescing and amplitude dependent damping in the wind-excited response of tall buildings

2014 ◽  
Vol 35 ◽  
pp. 108-117 ◽  
Author(s):  
Seymour M.J. Spence ◽  
Enrica Bernardini ◽  
Yanlin Guo ◽  
Ahsan Kareem ◽  
Massimiliano Gioffrè
Keyword(s):  
Natural Frequency ◽  
Tall Buildings

scholarly journals The Static and Dynamic Sensitivity of Magnetostrictive Bioinspired Whisker Sensor

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Ran Zhao ◽  
Qingjie Yuan ◽  
Jianwu Yan ◽  
Qanguo Lu
Keyword(s):  
Natural Frequency ◽  
Cantilever Beam ◽  
Vibration Frequency ◽  
Experimental System ◽  
High Sensitivity ◽  
First Order ◽  
Dynamic Sensitivity ◽  
Flow Sensing ◽  
Technical Indicator ◽  
Static Sensitivity

Magnetostrictive bioinspired whisker is a new kind of sensor that can realize tactile and flow sensing by utilizing magnetoelastic effect. The sensitivity is a key technical indicator of whisker sensor. The paper presented a new magnetostrictive whisker based on Galfenol cantilever beam, as well as its operation principle. Then, the static and dynamic sensitivity of the whisker sensor was investigated by using a self-made experimental system. The results illustrated that the proposed sensor has a high sensitivity. Its static sensitivity is 2.2 mV/mN. However, its dynamic sensitivity depends on the vibration frequency. When working at the natural frequency of the cantilever beam, the dynamic sensitivity performs an obvious increase—1.3 mV/mN at 3.5 Hz (the first-order natural frequency) and 2.1 mV/mN at 40 Hz (the second-order natural frequency), respectively.

Dynamic Response of a Servovalve Controlled Hydraulic Motor Driven Centrifugal Pump

1996 ◽  
Vol 118 (2) ◽  
pp. 253-258 ◽  
Author(s):  
Liangji Xu ◽  
John K. Schueller ◽  
Roy Harrell
Keyword(s):  
Centrifugal Pump ◽  
Natural Frequency ◽  
Damping Ratio ◽  
Experimental System ◽  
Estimation Procedure ◽  
Dynamic Responses ◽  
Physical Parameters ◽  
Model Estimation ◽  
Hydraulic Motor ◽  
Output Flow

A servovalve controlled hydraulic motor driven centrifugal pump was dynamically modelled using linearized analysis. The expressions for the system gain, natural frequency, and damping ratio in terms of component physical parameters were derived. An optimization model estimation procedure was developed and applied to the step responses of such a system constructed of common commercial components. The experimental system had a 4.2 Hz natural frequency and 1.2 damping ratio. The research indicates that the dynamic responses of a servovalve controlled centrifugal pump can be appropriately modelled for applications in industry and agriculture where the output flow rate needs to be dynamically changed.

Soil Grouting as Seismic Liquefaction Countermeasure

2014 ◽  
Vol 1025-1026 ◽  
pp. 1035-1040 ◽  
Author(s):  
Ahmet Pamuk ◽  
Patricia Gallagher ◽  
Korhan Adalier
Keyword(s):  
Colloidal Silica ◽  
Lateral Spreading ◽  
Liquefaction Resistance ◽  
Seismic Liquefaction ◽  
Ground Deformations ◽  
Centrifuge Tests ◽  
Liquefiable Soil ◽  
Soil Deposits ◽  
Vertical Ground ◽  
Similar Soil

This paper presents a series of centrifuge tests studying the performance of colloidal silica grouted soil layers during permanent lateral ground deformations due to earthquake induced lateral spreading. Two centrifuge tests were conducted to study liquefaction resistance of liquefiable soil deposits stabilized with colloidal silica, and then the results were compared with the tests conducted on similar soil deposits without any soil remediation. The testing results on remediated soils showed excellent resistance against the liquefaction and associated lateral and vertical ground deformations.

Tuned Liquid Damper Experiment Using Shaking Table

2013 ◽  
Vol 421 ◽  
pp. 772-777 ◽  
Author(s):  
Ki Pyo You ◽  
Young Moon Kim ◽  
Jang Youl You
Keyword(s):  
Natural Frequency ◽  
Damping Ratio ◽  
Tall Buildings ◽  
Excitation Amplitude ◽  
Shaking Table ◽  
Tuned Liquid Damper ◽  
Tuned Liquid Dampers ◽  
Liquid Dampers ◽  
Water Tanks ◽  
Wind Induced Vibration

The present study examines the characteristics of rectangular and circular tuned liquid dampers, which control wind-induced vibration in tall buildings, according to the natural frequency. The tuned liquid dampers (TLD) were of frequencies: 0.44Hz, 0.55Hz, 0.64Hz and 0.73Hz. The tuning feature of TLD water tanks was better in circular water tanks than in rectangular water tanks. Excitation amplitude affected the damping ratio based on energy dissipation capacity. At low excitation (below 5mm) and low natural frequency (0.44Hz), circular water tanks were advantageous over rectangular water tanks. However, at high excitation (over 5mm) and high natural frequency (over 0.55Hz), rectangular water tanks were advantageous over circular water tanks.

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