Buckling design of large steel silos with various slendernesses

Abstract

Large steel silos are typical kinds of thin-walled structure which are widely used for storing huge quantities of granular solids in industry and agriculture. In the present analyses, the buckling design of large steel silos subject to Eurocode-specified solid pressure is demonstrated. The finite element model is established using the commercial general purpose computer package ANSYS. Six types of buckling analyses are carried out for the geometrically perfect and imperfect models with and without consideration of material plasticity. The load cases of concentric discharge, discharge patch load, large eccentricity discharge, and large eccentricity filling are considered. The buckling behavior of six example steel silos with capacities of 30 000–60 000 m³ is investigated. The silos’ slenderness ranges from 4.77 to 0.35, comprising very slender, slender, intermediate slender, squat, and retaining silos. The index called the ratio of capacity to steel consumption (RCS) is initially defined in the paper, which provides an effective measure for the economical design of steel silos. It is validated that the RCS index increases rapidly with the decrease of silo slenderness, and the storage efficiency of steel silo improved greatly as the slenderness changes from slender silo to retaining silo. The effects of patch load reveal that the buckling modes in the case of discharge patch load are very different from those of silos under concentric solid pressure, and the effect is unfavorable for buckling resistance of all levels of slenderness of the example silos, but contributes a small decrease to the RCS index (less than 10%). The buckling deformations from both the linear and nonlinear buckling analyses in large eccentric discharge are strongly asymmetrical arising from the circumferential and meridional non-uniform distribution of the solid pressures. The buckling is mainly governed by the non-uniform distribution of the solid pressure other than other influential factors such as the weld imperfection, geometrical and material nonlinearity, compared with the load case of concentric discharge. The RCS index of example silos under large eccentric discharge is reduced substantially, and is approximately half that of silos under concentric discharge. The linear and nonlinear buckling deformations in large eccentric filling are also asymmetrical, deviating from the center to the side where the most friction locates to the highest wall contact. The RCS index of example silos under large eccentric filling is also reduced substantially, and is approximately 70% that of silos under concentric discharge. This reveals that the large eccentricity both in discharging and filling could result in a strong decrease of storage efficiency of steel silos.

中文概要

目 的

大型钢筒仓结构在正常装卸料过程中极易发生各 种失稳破坏。本文旨在分析多种长细比的大型钢 筒仓结构在散料荷载作用下的屈曲性能, 为结构 的稳定设计提供理论依据及技术支持。

创新点

1. 提出散料荷载作用下大型钢筒仓结构屈曲分析 的4 种典型工况: 轴对称卸料荷载工况、小偏心 卸料荷载工况、大偏心卸料荷载工况和大偏心装 料荷载工况; 2. 建立了适用于不同屈曲分析类型 的多种数值模型, 研究了结构的稳定性能, 并分 析了各种非线性、初始几何缺陷、仓壁厚度的分 布和基底嵌固刚度等对结构稳定性能的影响。

方 法

1. 根据不同工况下散料荷载分布的特点和屈曲分 析类型的差异, 通过非线性有限元方法, 研究结 构在四种散料荷载工况下的稳定性能; 2. 通过研 究结构在各种非线性屈曲分析下的荷载-位移全 过程响应, 确定结构的屈曲临界荷载和结构的稳 定承载力; 3. 比较各种荷载工况下结构的屈曲临 界荷载、屈曲模态及仓壁厚度分布特点, 分析结 构用钢量指标的变化。

结 论

1. 非线性屈曲分析的荷载-位移曲线是高度非线性 的, 不同长细比钢筒仓的屈曲平衡路径之间有较 大差异。2. 钢筒仓结构的屈曲延性随长细比的减 小而显著增大。3. 材料非线性对结构的稳定性极 为不利; 几何非线性和初始几何缺陷对结构稳定 性能的影响与结构的长细比密切相关。4. 壁厚的 分布对钢筒仓的稳定承载力和屈曲模态影响很 大; 设计时应考虑仓壁壁厚的不同组合形式, 并 确定使结构取得最大稳定承载力的仓壁最优分 布形式。5. 装料或卸料过程中的偏心使结构的储 存效率(容耗比指标)显著降低。