Research On Earthquake Simulation Experiment And Uplift Response Of Cylindrical Unanchored Liquid Storage Tanks

Large vertical cylindrical unanchored tanks are widely used in oil reserve bases for the advantages of less investment, smaller footprint, smaller respiratory loss, lower energy consumption and easer operation and management. The security and reliability of the liquid storage tanks in using has become extremely important. Once the liquid storage tanks are destructed under a seismic disaster, significant economic losses and environmental pollution would be brought out, even more, the human life safety may be threated.An earthquake simulation experimental research of the cylindrical unanchored liquid storage steel model tanks has been taken on a seismic test table. The effects of a variety of factors were considered. Uplift responses of the model tanks under earthquake have been systematically studied. The main tasks of this work are listed as follows:(1) A large-scale earthquake simulation experiment about the cylindrical steel liquid storage model tanks has been completed. Experimental procedures and data processing methods were introduced in detail. The selection of test equipment, the experimental methods, the design and production of the model tank, the sensors, the data acquisition systems, the test point arrangement method, the experimental seismic excitation and its input methods were described systematically. The experimental model systems included a tank without water, a tank with half water, a tank with full water and a tank with floating roof. The seismic excitation included the measured natural waves, artificial waves, white noise waves and harmonic waves.(2) Acceleration dynamic response of the model tanks were tested and analyzed. The analysis method of the acceleration time history experimental data were described. A common problem in the experimental studies that the multiple sampling devices are not synchronized and measurement results were different is solved. The spectrum characteristics of the model tanks were studied basing on the results of acceleration experiment results, the analysis methods and experimental results of the model tanks were introduced. ANSYS finite element software was used to simulate the low order natural frequency and fundamental frequency of the model tank systems, which were also calculated according to the national design standard. The reasons for the existence of consistency and differences between the results obtained from experiments, numerical simulation and national design standard were discussed.(3) The impact of earthquake multidimensional characteristics to the vertical absolute displacements and uplift response were studied. A point was proposed that the vertical absolute displacement and uplift response should be concerned simultaneously. The effects of different excitation’s direction were compared, which verified the necessity to carry out an analysis on dynamic response of tanks under multidimensional earthquake. Model tank responses under one-dimensional and multidimensional seismic excitation were compared; it showed that the uplift values under the latter were much higher than that under the former. And a further study were carried out about the effect of the changes of Z component in earthquake excitations, experiment results showed that the effect was significant to the uplift response.(4) Varieties of important factors were studied to investigate the impact of the dynamic laws of the model tank. The height of liquid in the tanks, with or without a floating roof, seismic wave acceleration amplitude, seismic wave frequency, site classification, etc. factors were considered as parameters. Under above factors and combined effects, laws and mathematical expressions of displacement and up lift response behaviors were got under experimental ways.(5) Dynamic fluid pressure was got by the tests, and rain flow counting method was used under seismic loading in this study. The mean pressure throughout the vibration process, the pressure amplitude and the effective amplitude of the cumulative number of cycles factors were considered to describe the strength of the dynamic fluid pressure, and the tank uplift responses to above factors were discussed.We would like to acknowledge the financial support from the Key Projects of "863" High-tech Research Development Plan (Project No.2009AA044803), National Key Technology R&D Program (Project No.2011BAK06B02).