地基沉降下油罐罐壁的变形分析

Research of the displacements in oil storage tanks caused by foundation settlement

储罐地基沉降常引起罐壁的几何变形,严重危害储罐的运行安全。基于地基沉降的实测数据,采用有限元方法研究地基沉降下大型浮顶石油储罐的结构变形响应。有限元模型中,综合考虑了环墙式地基、加强圈及肋板、抗风圈及支撑、包边角钢等实际结构,以及材料特性对罐壁变形的影响。采用Fourier级数将储罐地基沉降的实测离散数据拟合为若干阶谐波组合的形式,模拟地基单次谐波沉降对罐壁变形的影响,在此基础上,提出地基组合谐波沉降在最高液位下引起的罐壁径向变形公式,并与有限元仿真计算结果进行对比,结果表明,两者吻合较好,此拟合公式可普遍用于工程实践中10×104m3大型储罐地基沉降引起的罐壁变形计算,评估在役储罐的运行安全。

As is known,the foundation deposition of the oil storage tanks tends to lead to the deformation of the tank-shell wall which may bring about serious risks which may endanger the running safety of the oil tanks. To avoid the trouble,the present paper has done an investigation of the distortion behavior of the large-scale floating-roof oil tanks under the foundation deposition by way of the finite element method based on the field testing data of the foundation deposition. To solve the said problems,the paper has done a detailed study of the material for the tank-making,and traced and examined the non-linear geometrical feature that may involve the tank foundation with the concrete ringwall,unanchored bottom with the slope,the annular and sketch plates of the bottom and other various aspects of the tank foundation,for example,the tapered shell thickness,the stiffening rings and supports,the wind girders and supports,the top angles and other appurtenances in the 3-D finite element model of such tanks. The scattered measuring data of the tank foundation deposition due to the irregular shape can be represented as a Fourier series. Therefore,the deformation effects of the tank shell caused by the foundation single harmonic settlement can be simulated through the finite elements. The relationship among the parameters,such as the fluid level,the differential deposition and the roundness of the shell can be traced when the single harmonic deposition of the foundation has been formulated. Thus,it has turned out that,the radial deformation of the tank shell at the location of the liquid level increases with the increase of the harmonic number when n equals to2-4,though the radial deformation of the tank shell may decrease with the increase of the harmonic number when n equals to5-6. Thus,the radial deformation of the tank shell may also increase with the growth of the foundation harmonic settlement amplitude. Therefroe,it is just on the aforementioned basis that the present paper has put forward the fitting formulae of the simulation data on the radial deformation of the tank shell resulted from the combination harmonic settlement when the tank is filled up to the maximum design height with the due liquid,a fact of our comparison between the fitting formulas and the FEA method. What is more,since the calculation formula can be well compared with the numerical simulation,it can be successfully applied to the out-ofroundness evaluation of shell induced by the foundation settlement of the oil tanks with a capacity of 100 000 m3 in the engineering practice.