Stability Analyses Of Large Circular Steel Silos Subject To Solid Pressure And Wind Load

In the past several years, steel silos are in great need with the development of industry and agriculture, especially for urgent need of large capacity silos. Some steel silos are even more larger with capacity more than 100,000m3, which throw out a new challenge to rational design of silo structure. Steel silos are often filled or discharged with eccentricity during normal service of life, which would lead to nonuniform distribution of solid pressures both in the meridional and circumferential directions and result in significant decrease of buckling strength. The wind induced collapse of steel silo in the past several decades had also been reported during normal service or during construction. It is of great significance to carry out buckling investigation of steel silos under eccentric solid filling or discharging pressures, and the combinational wind pressure for practical reference.Six large circular steel silos with capacity of 30,000～60,000m3 referenced in practical engineering are chosen as illustrative examples. The examples cover every category of silo slenderness:the very slender, slender, intermediate slender, squat, retaining silo, and also cover a very wide range of silo geometry. The buckling behavior of steel silos is investigated using the commercial general purpose finite element computer package ANSYS by taking account of the geometrical nonlinearity, material nonlinearity, weld initial imperfection. The layout is organized as follows:1) The research of distribution of solid pressures are introduced for China and European design code, and the design methods from the two codes are also compared.2) The numerical investigation on buckling behavior under conccentric discharge is presented for example silos. The economic index called the ratio of capacity to steel consumption (RCS) is initially defined in the paper, which provides an effective measure for economical design of steel silos. The parametric analyses are also carried out for evaluation of the influence on the buckling resistance of steel silo:the thickness distribution of silo wall, the abrasion of stored solid, the fabrication quality, and the wall surface class, etc.3) The buckling behavior of example silos subject to eccentric discharge is carried out, and the effects of patch load on buckling behavior of example silos are firstly evaluated to account for accidental asymmetries during discharge. The effect of patch load position, amplitude, eccentricity on buckling behavior of example silos is investigated, both the buckling strength and buckling modes are provided. The load case of large eccentricity discharge and multiple outlet discharge are also introduced. Buckling behavior of example silos subject to large eccentric discharge is evaluated, by consideration of the impact of eccentric flow channel radius, wall contact angle, characteristic depth, amplitude of eccentricity, the most unfavorable radius ratio etc, on buckling behavior of steel example silos.4) The load case of large eccentricity filling is introduced and the reason for the loading condition is explained. The top surface pile during filling or when the silo is full may be formed with a large eccentricity, resulting in unsymmetrical solid pressure on the wall and the unsymmetrical meridional stresses. Buckling behavior are evaluated for the intermediate and squat example silos when the structures are filled with large eccentricity greater than 0.25 time the silo diameter. The effects of amplitude of filling eccentricity, slope of solid pile, aspect ratios are evaluated on buckling strength and buckling modes of silos.5) The wind induced buckling behavior of example silos are investigated by two load cases: WE (wind and empty silo) and WF (wind and full silo). The concept of critical wind velocity is initially put forward and defined for wind induced buckling analysis, under which the silo structure obtains the equivalent buckling strength in Load Case WE and WF. The dominant loading condition by either Load Case WE or WF can be determined by comparisons between the critical wind velocity and the designed wind velocity proposed by the meteorological conditions. The dominant load case for buckling design of silos with aspect ratios ranging from 0.4 to 8.0 are presented and the wind induced buckling strength and buckling modes are discussed.6) A novel type of silo structure designated as cellular silo, is initially put forward and discussed. Structural system is firstly determined for cell silo by comparisons between the shell model and frame-shell models, and it is showed that the frame-shell structure composed of shell elements and beam elements for cell silo is feasible, which is quite distinct from the shell structure fit for circular silo. Buckling behaviors of group silos including combinations of two cells, three cells, four cells and cellular silo are investigated by considerations of load cases defined according to the number of working cell silos and their relative position in the group. The design methods are summarized for determination of load cases and buckling analyses of cellular steel silos. The influence of eccentricity during discharge on large circular and cellular steel silos are also compared in detail. The relevant results can be adopted for direct design use of practical silo engineering of this new type.