| In recent years,In recent years,with the development of the national strategic petroleum reserve base,the construction of the storage tank and the large oil tanks has reached an unprecedented peak,large and ultra-large oil storage tanks have developed rapidly and become large and centralized.However,as the capacity and the diameter of the tank increased,the characteristics of the short cylindrical thin shell structure of the tank also deteriorate.Due to the high moisture content and low bearing capacity of the saturated loess foundation,the storage tank foundation usually produces various types of subsidence under the load of internal hydraulic pressure and earthquake,and the foundation settlement will pose a serious threat to the normal operation and safety of the storage tank.In addition,seismic action not only causes structural instability and loss of bearing capacity,but also can cause serious secondary disasters such as fire and explosion.Therefore,this paper is based on the first large-scale oil storage tank project constructed in saturated loess area,which is of great practical significance for the long-term safety and smooth operation of the storage tank under the condition of the saturated loess foundation,the mechanism of the composite foundation of the CFG composite foundation,the joint action of the tank foundation and the foundation,the stress and strain distribution of the tank,the seismic response of the tank,the evaluation of the seismic capability,etc.The main research content and innovation are as follows:(1)The static load test on the bearing characteristics of CFG monopile and monopile composite foundations was carried out,and the ultimate bearing capacity of CFG monopile and monopile composite foundations was obtained.One of the 150,000 m~3 oil storage tanks was selected,a deformation monitoring section was set up in the tank area,test elements were buried in the foundation,and on-site monitoring of the foundation of the tank was carried out during the tank filling test pressure.The centrifugal model test was used to simulate the stress level of the foundation soil and to compare and analyze the deformation development characteristics of the saturated loess foundation and the CFG pile complex foundation under tank load.The study shows that the rigid CFG pile can transfer the larger load to the pebble layer and play an end bearing effect,and the characteristic value of the treated composite foundation bearing capacity is 275 kPa,which meets the design requirements.The pebble layer beneath the saturated loess layer quickly dissipates the supra-static pore water pressure caused by external loading,and foundation settlement stabilizes relatively quickly.After the tank is filled with water,the load transferred to the foundation surface through the ring beam foundation is larger,causing the foundation settlement deformation under the ring beam foundation to increase.At different locations in the tank bottom plane,there are differences in pile-soil pressure,the base pressure tends to increase first,then decrease,and then increase as the radius increases.basically the"M"shape.(2)The numerical calculation method was used to establish the CFG pile finite element model,and analyzed the load level,pile length,pile modulus,technical parameters of the mattress layer,replacement rate and other influences on the load bearing performance of CFG piles.In the hypothetical displacement model,inter-pile soil compression expressions and simplified algorithms are derived for the CFG composite foundation reinforcement zone under flexible loading,taking into account pile soil interactions.The study shows that,through the regulation of the mattress layer,the compression of the upper inter-pile soil is greater than the settlement of the pile,there is a negative friction zone,and the ratio of the neutral point depth to the lower limit depth of the settling deformation of the soil layer around the pile is about 0.5.Since the rigidity of the bottom plate of the tank is very small,the loading of the tank can be assumed to be a large area of flexible loading,ignoring the compression deformation of the pebble layer at the end of the pile,the simplified method is used to calculate the settlement of the CFG pile composite foundation compression layer is more consistent with the actual results.The composite modulus method,on the other hand,exaggerates the role of the pile body and calculates small results.(3)Field testing of 150,000 m~3 large crude oil storage tank using resistance strain measurement technique to obtain the stress level and change pattern of tank wall and ring beam.A finite element model of the tank-foundation-foundation system is built,and the analysis of ring beam stress,wall ring stress,bottom plate settlement and stress is carried out,and the results of numerical simulation calculations are compared and analyzed with the results of the field water filling test.Finite element analysis of the stress and deformation of the tank floor,local stress of the tank,and quantitative analysis of the local warpage of the tank floor and bending stress of the large angle weld are conducted.The study shows that,when the maximum water loading,the maximum wall annular stress is located at 3.34m from the upper surface of the tank bottom,the maximum value is 284.9MPa,the axial compressive stress at the bottom plate connection is larger,the maximum is about 210MPa.The bottom plate radial bending stress and annular stress both occur in the tank bottom plate and the tank wall connection at the large angle weld,the radial bending stress is about 2.7 times the annular stress.The bottom plate of the tank has a reverse"warpage"phenomenon,the maximum warpage height is 4.8mm,the windproof ring and strengthening ring effectively control the radial displacement of the tank wall,but it makes the tank wall annular stresses and axial forces fluctuate near the reinforcing and wind-resistant rings.(4)ANSYS is used to establish the finite element analysis model of the tank,considering the fluid-solid coupling between the tank and the storage fluid and the potentiation effect of strengthening ring and windproof ring,and to conduct modal analysis of the tank at different storage fluid heights.Displacement time response and stress time response analysis were performed by inputting the Tianjin Ninghe Wave.Studies have shown that the setting of a reinforcement ring and an anti-wind ring has a greater effect on the higher-order frequency of the tank,as the liquid level rises,the lower order frequency of the tank increases and the higher order frequency decreases.At the same time,the wind resistance ring and reinforcement ring can effectively reduce the amplitude of the maximum displacement and stress,so as to control the displacement and stress of the tank,without damage due to prematurely reaching the limit displacement and yield strength.When acceleration reaches its peak,the storage tank's overall annular stress maximum is 744 MPa,which is close to the material's ultimate tensile strength,and the tank may locally undergo strength damage.With a maximum displacement of 168mm,the structure of the tank is in the plastic stage,and the plastic properties of the material can be exploited in the seismic-resistant design.According to the standard formula,the storage tank in the range of 0m to 22m filling height storage liquid,all are capable of meeting the seismic protection requirements for an8-degree design earthquake(equivalent to 475 years). |
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