Stress Analysis And Aseismatic Research Of Large Unanchored Oil Storage Tanks

The large unanchored oil storage tank is the key equipment of the national strategic oil storage reservoir. Recently, the large-scalization becomes its development tendency. Failures of these tanks will be terrible. Therefore, it is very important to research on the stress condition and safety assessments of these tanks. Based on the filed testing of stresses, the static strength analysis and aseismic research of the 15×10~4m~3 oil tanks constructed lately in china have been conducted by the mechanic model and finite element numerical simulation. The main study is presented as follows:A new method called Long-Short Cylindrical Shell Method has been proposed to calculate the stress in wall of the large unanchored oil storage tank. In this method, the first shell plate is regarded as a short cylindrical shell. And all the other shell plates are considered as the long cylindrical shells. In addition, the Elastic-Inflexible foundation beam-coupling model is applied to the tank-bottom annular plate. Then, the stress calculation formulas are deduced to estimate the stress distribution in the tank wall and bottom plate. This research indicates that the theoretical values calculated by the new method match the stress testing results very well and the calculation is very simple. Therefore, the new method is suitable to the engineering application.By the watering experiment of the 15×10~4m~3 tank with the floating roof, the field testing has been carried out to evaluate the stress in the wall and bottom plate of the oil storage tank. In this testing, a lot of meaningful data have been obtained, which proved that the resistance strain measuring technique is a feasible method to test the stress of the large oil storage tank.Considering the uncertainty of the foundation coefficient during the finite element modeling of the large unanchored oil storage tank, a new model has been put forward to deal with the contact condition between the ground and bottom plate of the storage tank. In this model, the foundation settlement difference between the reinforced concrete wall and the elastic foundation under the bottom plate of tanks is used as the boundary conditions. This new model improves the calculation accuracy in the bottom plate greatly.Moreover, great achievements have been obtained to the design and safety assessments of the large oil storage tank according to the above results.In this paper, the three-dimension finite element method is used to calculate the dynamic characteristics of the solid-fluid coupling system of large oil storage tanks. The influences of the liquid density and level height on the natural frequency are studied. The results indicate that the natural frequency decreases with the increase of the liquid density and level height.In this paper, the quasi-static method for the simulation of the elephant foot buckling is summarized. Some improvements for this method have been proposed. In addition, a new dynamic modeling method of the elephant foot bucking under the re-uplifting condition of the local bottom plate is put forward. The research proves that the internal pressure due to the axial compressive stress and the circumferential membrane causes the buckling of the tank wall. However, the axial compressive stress is the predominant factor for the buckling of the tank wall, which is in accordance with the international aseismic standards.