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Dynamic Behavior of Overhead Water Tank Using Shake Table Tests


Published on Feb 19, 2019

Abstract

The structures are subjected to static and dynamic loads. However, the majority of structures are designed for static loads and the effect of dynamic loading is not considered. It has been well established that during earthquake, a number of buildings fail and the effect is much more severe when there is a resonance. Resonance occurs when the frequency of base motion coincides with the natural frequency of the structure. Hence, natural frequency of the structure forms a key parameter for the stability of structures during an earthquake. Elevated water tanks consist of huge water mass at the top with slender columns. The behaviour of overhead water tank during earthquake is more critical than static loading. It is well documented that majority of water tanks fails during earthquakes.

The scope of the present work is to compute the natural frequency of overhead water tank model using shaking table setup and by analytical study.

The behavior of water tank models under static and dynamic loads is studied. The overhead tank model comprises of four columns, an aluminum base plate and acrylic tank. The models are idealized as a single degree of freedom system and continuous models. The models are subjected to sinusoidal base motion of varying frequency and amplitude. The experimental setup consists of shaking table, acceleration sensors and data acquisition system.

Keywords : Dynamic loading, Natural frequency, Time period, Resonance, Cantilever action, SDOF system, Finite element method, Bending moments, Amplitude, Displacement, Sloshing height, Acceleration Sensors

Objectives:

To know the importance of model testing in earthquake engineering.

 To understand the suitability of existing shaking table test setup to conduct dynamic testing on water tanks.

 To construct the overhead water tank models using Aluminum plates and Acrylic sheets and to test its performance.

 To determine the natural frequency of overhead water tank experimentally and analytically.

 To compare the behavior of the overhead water tank models using experimental and analytical study.

Methodology

The scope of the present work is to compute the natural frequency of overhead water tank models using shaking table setup and to study the behavior of models under dynamic load. The overhead tank model comprises of four columns, an aluminum base plate and Acrylic tank. The models are idealized as single degree of freedom system. The models are subjected to sinusoidal base motion of varying frequencies and amplitudes. The experimental setup consists of available shaking-table and piezoelectric acceleration sensors for collecting the acceleration time history. The data is stored and processed using data acquisition system and DEWESOFT software. The effect of water on the walls will be studied experimentally. The water tank models are also analyzed using STAAD.Pro software for the static and dynamic loads and the results are compared with the results obtained by the shaking table test. The natural frequency is determined and also the dynamic characteristics are studied analytically. The behavior of water tank under dynamic load is studied both experimentally and analytically.

Scope For Future Work :

 The behaviour of water tank of different shapes and size under static and dynamic loading can be studied using analytical and experimental methods.

 Staging effect on the dynamic behaviour of water tank can be studied.

Conclusion:

 The value of natural frequency of water tank without water and with water upto small height obtained from both analytical and experimental method are in good agreement.

 Dynamic displacement is a function of forcing frequency and not a function amplitude.

 Natural frequency of water tank with water calculated from theoretical method is not comparable with the experimental values at higher water column. This may be because of the sloshing effect of water. The percentage of error is increasing with the height of water in the tank. Corrections need to be applied while calculating natural frequency of water tank analytically.

 Sloshing height of water increases with increase in height of water column in water tank when subjected to dynamic loading.

Project Done By Ms. Rajeshwari Shankar Naik, Mr. Rajeshasadashiva Naik, Mr. Subramanya G, Mr. K. Vishruth






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