Study On Strength And Stability Calculation Method Of Tank Wall For Large Oil Storage Tank

With the large scale of oil storage tank, the potential risk of tanks is increasing. The fracture of tank will result in a great loss. A large number of oil tanks designed according to current standards are still destroyed in all previous earthquake and hurricane disasters. In order to ensure the safety of large oil storage tank, further research on strength and stability calculation method of the tank should be earried out. In this thesis, strength and stability calculation methods of the tank wall in China, America, Japan and European oil tank design standards are deeply studied and compared, the shortcomings of these methods are also analyzed. On this basis, combining the latest study results inland and aboard, the theoretical study on the calculation methods of strength, critical loads of elephant foot buckling and wind pressure instability of the tank wall for large oil storage tank is developed. The presented results can provide technical support in further protection of large oil storage tanks. The main research works of the thesis include:(1) Thickness calculation methods of the oil tank wall in China standard GB50341, America standard API650, Japan Standard JIS B8501and European standard BS EN14015are first studied. Based on the theory of combined cylindrical shell, a new evaluation method for reasonable design of the tank wall is proposed. Applying this method, the effect of weld coefficient and allowable stress of steel plate on the tank wall thickness calculation is discussed in detail. Then, according to the shortcomings of the present China oil design standard GB50341, a reasonable tank wall thickness calculation method for large oil storage tank is presented after a lot of data comparisons and analyses, which can be used in Chinese engineering practice.(2) A new buckling critical stress calculation method for the tank wall which are accordance with actual failure mechanism of elephant foot buckling and conveniently applied for engineering calculation is established. Assuming axisymmetric buckling and according to the adjacent equilibrium criterion, a buckling critical stress formula of a perfect tank wall is first obtained through analysis of elastic-plastic buckling carried out by J2plastic flow theory. Furthermore, combining the current tank seismic design standards and the results obtained in this thesis, a new critical buckling stress formula of the tank wall is derived after correction for material plasticity by introducing a plasticity influence coefficient. Comparisons between the results obtained and those from the relevant formulae in the design standards of China, America, Japan and Europe are also performed. The research shows that under interaction of high hydraulic and axial compression, the material properties of the tank wall change rapidly, and the buckling strength of the tank wall also decreases rapidly.(3) The critical load calculation formula for wind pressure instability of the tank wall is deduced and obtained, which considers the effect of the actual stepwise variable thickness of large oil storage tank. Combining the separation of variables, perturbation method and Fourier series, a unified analytical method for the buckling of cylindrical shells with arbitrary axisymmetric thickness variation under uniform external pressure is presented. Adopting the arc tangent function to accurately describe the stepwise variable thickness of the oil tank, the analytical formula relating the buckling load to thickness values of the oil tank subjected to wind pressure is first derived in the world.