Steel Silos Research Articles

Imperfection sensitivity of locally supported cylindrical silos subjected to uniform axial compression

For the prediction of the real failure load of shell structures, such as locally supported cylindrical steel silos under axial compression, it is convenient to take into account imperfections. It is assumed that such silos are very sensitive to a wide range of (even small) geometric imperfections, and that they lower the failure load significantly. Furthermore, these imperfections caused by the fabrication or the manufacturing process, are the dominant factor in the discrepancy between the theoretical/numerical predictions based on a perfect geometry and the experimental results of an imperfect geometry. In other words, it is important to make a well-considered choice for an imperfection when predicting the real failure load. However, the imperfection sensitivity depends, among other things, on the shape of the shell, the stiffening configuration, the boundary and loading conditions, etc. Before proceeding to the calculation of interaction curves and the development of new design rules for imperfect barrels, it is essential to perform an extensive study to examine the influence of imperfections to the failure behaviour and to choose a sufficiently detrimental imperfection shape. In this study, different imperfection forms are numerically investigated: the linear bifurcation mode, the non-linear buckling mode, several post-buckling deformed shapes of the perfect shell, and a weld depression type A and B. Additional aspects, such as the orientation, the amplitude of the equivalent imperfection, and the position of the influence of the weld depression are also investigated. The present study takes into account the European normative documents and the guidelines of the recommendations of the ECCS.

Maize Storage in Termite Mound Clay, Concrete, and Steel Silos in the Humid Tropics: Comparison and Effect on Bacterial and Fungal Counts

Abstract. Considering the inadequacy of grain storage structures in Nigeria, which has been partly attributed to high cost and unavailability of construction materials, this study investigated the suitability of using readily available termite mound clay (TMC) for grain silo construction in comparison to conventional reinforced concrete (RC) and galvanized steel (GS) silos for maize storage in the humid tropics. The extent to which temperature and relative humidity affected the quality of stored grain during 8-month unaerated storage, covering both dry and rainy seasons, was evaluated using bacterial and fungal counts as performance parameters. The initial bacterial count of 3500 colony forming units (CFU) per gram (CFU g -1 ) increased to 120000, 11000, and 8800 CFU g -1 for TMC, RC, and GS silos, respectively. There was no fungal activity at the beginning of storage, but fungal activity increased to 1500, 5500, and 350 CFU g -1 in TMC, RC, and GS silos, respectively. Fungal activity was noticed in the TMC silo in the fourth month of storage, which coincided with the start of the rainy season. Fungal counts exceeded the acceptable threshold of 1000 CFU g -1 in the TMC and RC silos. Relative humidity was of greater significance than temperature in affecting all maize quality parameters considered. TMC was found suitable for constructing silos for short-term grain storage under unaerated conditions. Modification of the current TMC silo design to address permeability issues is expected to improve its performance for longer-term maize storage.

Experiment and simulation research of storage for small grain steel silo

Knowing the temperature distribution in silo is a convenient and efficient way to control the process of grain storage. A three-dimensional (3-D) numerical model was used to study the temperature variation in small grain steel silo under quasi-steady state. In this study, experiments were conducted and porous media model was adopted. Results of numerical simulation and experiment were compared and the results indicated that grain temperature was influenced by temperature of the wall, grain stacking height, and the distance between grain and wall. The higher the wall temperature, the more the temperature increases. If the wall temperature is low, the effect of wall temperature on temperature distribution is significant. The temperature at the top part of grain varied obviously with the changes of temperature in air layer. Overall, numerical simulation results coincided with experimental results and the model established in this study is valuable for predicting grain temperature in steel silo. Keywords: small grain steel silo, quasi-steady state storage, numerical simulation, porous media model, grain storage DOI: 10.3965/j.ijabe.20160903.1946 Citation: Zhang L D, Chen X, Liu H, Peng W, Zhang Z J, Ren G Y. Experiment and simulation research of storage for small grain steel silo. Int J Agric & Biol Eng, 2016; 9(3): 170－178.

Steel silo failure and reinforcement proposal

Abstract Steel silo failure is not a sporadic event in the industrial field. Sometimes the failure involves only a shell deformation that does not affect the structural integrity of the overall silos. In other cases, failure involves complete collapse of the structure that could affect the people's safety. In general three major causes of silo failure are identified: design errors, construction errors, and utilization errors. In this study, a buckling failure of the real silos used in a thermal power plant to store a granular solid material (limestone) is analysed. It has long been recognized that the buckling failure of the silos is due mainly to the eccentric discharge of its stored solid. The main reason for this kind of failure is due to the difficulty, in the design phase, to characterize the pressure distribution caused by eccentric solids flow (funnelling). In the present study, the pressures caused by eccentric discharge are characterized using the new rules of the European Standard EN 1991-4 that defines the “Actions in Silos and Tanks”. Using this new improved description of unsymmetrical pressures, it is now possible to perform relatively realistic calculations relating to this common but complicated shell buckling condition. The paper explores the structural behaviour leading to buckling during eccentric discharge and proposes a possible reinforcement design of the silos to minimize this kind of problems following the approach given in the European Standard EN 1993-1-6 “Strength and Stability of Shell Structures”.

Stability analyses of a cylindrical steel silo with corrugated sheets and columns

The paper presents comprehensive quasi-static stability analysis results for a real funnel-flow cylindrical steel silo composed of horizontally corrugated sheets strengthened by vertical thin-walled column profiles. Linear buckling and non-linear analyses with geometric and material non-linearity were carried out with a perfect and an imperfect silo by taking into account axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. Finite element simulations were carried out with 3 different numerical models (single column on the elastic foundation, 3D silo model with the equivalent orthotropic shell and full 3D silo model with shell elements). Initial imperfections in the form of a first eigen-mode for different wall loads and from 꼒n-situ. measurements with horizontal different amplitudes were taken into account. The results were compared with Eurocode 3. Some recommendations for the silo dimensioning were elaborated.

Optimal stiffening configuration for locally supported cylindrical silos: Engaged columns

Cylindrical steel silos are often supported by discrete supports or columns to be able to provide a hopper and to facilitate emptying operations beneath the cylindrical barrel. The simplest mean of support for a light silo is by the use of engaged columns, without the use of unnecessarily expensive ring stiffeners. Such engaged columns gradually introduce the support load into the silo wall by shear, spreading the stresses in circumferential direction. In general, the highest axial compressive stress concentrations can be found in the shell wall in the vicinity of the top of the engaged column, resulting in failure due to excessive yielding and/or local instability.The study aims to identify the optimal combination of dimensions of an engaged column (i.e. the height, the widths in circumferential and radial direction and the thickness) to obtain a failure load as high as possible with as little material in the column as possible. An important condition is the requirement that the columns must withstand a higher load than the silo wall itself. In other words, failure should occur in the vicinity of the terminations of the columns (and not in the column itself). All results and conclusions are based on numerical finite element analyses.

RATIONAL STEEL CORRUGATED PROFILE DESIGN

Purpose. The work sets forth the search results of new, more efficient design solutions for metal silos, namely, the analysis of existing types of profiles cross-section in a steel wall of such silo and development of less material-intensive section of corrugated profile.Methodology. To achieve the set goal there were researched the existing types of capacitive structure profiles and their strain-stress state under the load. The analysis was performed on the results of computational experiments. The prototype object was mathematical computer models. The calculations were made using the finite-element method. For computational experiment there was used the design-computing system Structure CAD for Windows. Findings. In this work there were obtained the data allowing to assess work of the profiles and to find more effective type of cross-section in terms of its material consumption. In the process of joint study of the authors a new type of profile for capacitive structures was developed; it has higher utilization efficiency and the attachment point of individual steel sheets with this type of profile. Both solutions are easy to install, reliable in operation and can be manufactured in the conditions of modern industrial production using standard equipment, materials and components. Originality. A new type of corrugated profile cross-section for steel silo walls was proposed; it has higher load carrying capacity and rigidity and allows reducing the metal thickness without changing the structure carrying capacity that results in material consumption reduction of the whole structure.For this and similar types of profiles there was designed and proposed the attachment point of individual corrugated sheets screwed with extending flange, which enables the unit connection in case of small size corrugations, where the distance is not sufficient to accommodate the bolt cap between the individual corrugations. Practical value.Application of the proposed solutions can increase efficiency, manufacturability and maintainability of steel silo wall structures.The results obtained during the research show promise for further development of research on finding new and more economic solutions for corrugated steel silo wall design, as well as other ways to reduce material consumption of bulk material storage structures.

Stability of cylindrical steel silos composed of corrugated sheets and columns based on FE analyses versus Eurocode 3 approach

Comprehensive static and dynamic 3D stability finite element analyses of a cylindrical steel silo composed of corrugated sheets and open thin-walled vertical stiffener profiles were carried out by taking the geometric and material non-linearity into account. The silo was subjected to axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. Theoretical and measured initial geometric imperfections were considered in calculations. The results of non-linear analyses were compared to those according to Eurocode 3. Modifications of the Eurocode formulae were proposed. Some recommendations for the silo engineering design were elaborated.

THE STRUCTURAL ANALYSIS OF STEEL SILOS WITH CYLINDRICAL-WALL BEARING AND PROFILE-STEEL BEARING

The silos are widely used in bulk material in many fields such as agriculture, mining, chemical, electric power storage, etc. Thin metal cylindrical silo shells are vulnerable to buckling failure caused by the compressive wall friction force. In this paper, the structural analysis of two types of steel silo with cylindrical-wall bearing and profile-steel bearing is implemented by Abaqus finite element analysis. The results indicate that under the same loading conditions, steel silos with profile-steel bearing and cylindrical-Wall bearing have similar values in Mises stress, but the steel silo with profile-steel bearing has a smaller radial displacement and a better capability of buckling resistance. Meanwhile, the total steel volumes reduced 8.0% comparing to the steel silo with cylindrical-wall bearing. Therefore, steel soil with profile-steel bearing not only has a less steel volumes but also a good stability.

Electrodeposition of Ni–GNS–TiO2 nanocomposite coatings as anticorrosion film for mild steel in neutral environment

In this article nanocomposites of graphene nanosheets–anatase titanium dioxide (GNS–TiO2) were prepared via hydrothermal method. In this method graphene oxide (GO) was reduced to graphene nanosheets (GNS) simultaneously with anatase (TiO2) growth in situ on the graphene nanosheet (GNS) surface. The resulting GNS–TiO2 nanocomposite was characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). The percentage of TiO2 in the prepared GNS–TiO2 was determined by thermo gravimetric analysis technique (TGA). The fabricated GNS–TiO2 nanocomposite was codeposited with Ni by electrodeposition technique and used as a protective film for mild steel used in construction of steel silos. Different operating conditions for the deposition process were adopted to obtain Ni–GNS–TiO2 nanocomposite coatings with good morphological properties. The Ni–GNS–TiO2 nanocomposite coatings were characterized using a field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray analysis (EDX). Moreover, Ni–GNS–TiO2 nanocomposite coatings were subjected to different electrochemical and mechanical tests to evaluate their corrosion behavior and hardness in comparison with that of pure Ni coating. It was found that the corrosion rate of the Ni–GNS–TiO2/mild steel electrodes decreases and the microhardness increases with increasing the wt.% of GNS–TiO2 nanocomposite in the prepared electrodes. The best corrosion resistance value of 33.1kΩcm2 and relatively high hardness value of 478HV were recorded for the composite coating electrode that contains 20.4wt.% GNS–TiO2 compared with the other composite coating electrodes or pure Ni coatings.

Influence of storage conditions on the quality properties of wheat varieties

Effects on the quality properties in real storage conditions and galvanized steel silos for wheat varieties (cv. Bezostaya and Lancer) in the 180 day storage period were investigated. The wheat quality properties including grain moisture, crude protein, hectoliter weight, thousand grain weight, Zeleny sedimentation, wet gluten, dry gluten, and falling number were monitored in the laboratory in three replicates at regular intervals. From these results, crude protein, hectoliter weight, and thousand grain weight of Bezostaya and Lancer wheat varieties decreased with an increase in storage period. Grain moisture, Zeleny sedimentation, wet gluten, and dry gluten increased with storage period until the first two months and subsequently decreased. However, grain moisture for Lancer wheat increased until the third month of storage, after which it decreased. Falling number increased with increase in storage period.

Effects of Different Storage Conditions on the Nutritional Qualities of Barley and Maize

The effects of different types of storage on nutritional quality values of barley and maize are examined. For this purpose, 3 different storage types, including horizontal-reinforced concrete storage, vertical-reinforced concrete silo and verticalsteel silo were taken into consideration. Nutritional quality values (dry matter, crude protein, crude fat, crude fiber, crude ash, and metabolizable energy) of samples were analyzed in the laboratory in four replicates. Total of 438 samples were collected from each of the stored product stacks during the storage for 12 months. Total average nutritional value losses have been found for barley were 1.74% in horizontal-reinforced concrete storage, 1.23% in reinforced concrete silo, 2.82% in vertical steel silo. These values have been found accordingly as 6.21%, 3.02%, and 2.04% for maize stacks. As a result of this research, the vertical steel silo was determined to be more appropriate for maize storage while the horizontal-reinforced concrete storage structure and vertical reinforced concrete silo were suitable for barley storage

Finite element analysis and experimental research on mechanical performance of bolt connections of corrugated steel plates

Fabricated corrugated steel silos are widely used for grain storage, and the corrugated steel plates with bolt lap connections are often used as the silo wall. This paper aims to research the mechanical performance of bolt connections of corrugated steel plates. Experiments were conducted for eight groups of specimens subjected to various parameters. The finite element models took into account the material nonlinearities, geometry nonlinearities and contact nonlinearities. The major factors (plate thickness and wave height) were selected, and parametric studies were performed. It is found that the ultimate bearing capacities of corrugated steel plate specimens are smaller than those of the flat steel plate specimens, and the ultimate displacements of the former are larger than those of the latter. The attaching degree between the nuts and the steel plates is a primary factor of the difference. The finite element results are in good agreement with the experimental results. The ultimate bearing capacity of single-bolt connections of corrugated steel plates shows an increasing trend with the increase in plate thickness, and the ultimate displacement and ultimate bearing capacity both increase as the wave height decreases. When the wave height of the specimen decreases to 0 mm, the ultimate bearing capacity and ultimate displacement increase significantly.

Elastic failure of locally supported silos with U-shaped longitudinal stiffeners

For practical considerations, thin-walled steel silos are often supported by a limited number of discrete equidistant supports around their circumference. In such cases, large loads are transferred to the limited number of supports, causing locally high axial compressive stress concentrations. A possible solution is to add a partial-height U-shaped longitudinal stiffener above each support. Such stiffeners create a more gradual transmission of vertical loads to the supports, increasing the maximum failure load. This paper aims to map the influence of the dimensions of such longitudinal stiffeners on the failure behaviour of a thin-walled silo. Both the parameters of the cross-section and the height of the stiffeners are discussed. All the results and the findings are based on geometrically and material nonlinear analyses — GMNA — performed with finite element software. The simulations indicate that, in general, thin-walled silos will fail by pure elastic buckling in the unstiffened silo wall above the terminations of the longitudinal stiffeners. However, this is only true if the cross-section of the stiffeners, and to a lesser degree the moment of inertia, is sufficiently large in order that the longitudinal stiffeners can absorb the supporting loads. In contrast, for longitudinal stiffeners with a small cross-section, the silo structure will fail by premature elasto-plastic collapse of the stiffeners itself at significantly lower load levels. Furthermore, the height of the stiffeners and the degree of support - the circumferential width of the supports and the stiffeners is equal to each other — are the most important geometrical parameters which are beneficial to reach a maximum load level for a specific silo. Finally, the buckling behaviour and the failure load are hardly influenced by radial width and the thickness of the longitudinal stiffeners.

Research of Stability of Cylindrical Steel Silos with Lap Joints

Steel silos are commonly constructed by welding together a large number of curved steel panels with lap joints.Where the lap runs horizontally around the silo circumference, the lap connection causes a local eccentricity in the line of vertical thrust in the shell wall. This eccentricity induces high local bending stresses, which are detrimental to the stability of the structure. This paper chooses a flat-bottom squat steel silo as the research object to analyze the stability of lap-jointed steel silo by comparing with a butt-jointed steel silo. By stressing loads calculated according to Chinese code for design of grain steel silos, considering two load cases including axial compression only and combined axial compression and internal pressure, this paper performs numerical analysises including linear buckling analysis, geometric nonlinear elastic analysis and geometrically and materially nonlinear analysis to study the effects of material nonlinearity and lap joint on stability.

The Finite Element Analysis of Temperature Effects on Large Flat-Bottom Squat Steel Silos

Steel silos lack of systematic theoretical research. Based on a large floor-ash steel silo, for example, in view of a large number of documents based on the relevant specifications, the temperature load of steel silo effect is analyzed. The results show that: for those steel silos which are constructed in a larger temperature difference between regions, warehouse wall stress induced by the temperature load can not be ignored; at the bottom of the storehouse, the hoop stress, vertical stress load vary linearly with temperature, therefore, when the temperature difference is large, the temperature stress at the bottom of the warehouse is much larger than the warehouse wall stress induced by the storing load; the temperature stress at the bottom of the steel silos changes in shape of a parabola according to the silo diameter and the warehouse wall thickness. Therefore, in a certain range, reducing the diameter of the silo but increasing the thickness of the steel silo warehouse is harmful to the steel cylinder.

Nonlinear Dynamic Behavior of Granular Materials in Base Excited Silos

Nonlinear behavior of granular materials stored in steel silos subjected to dynamic base excitation due to earthquake is presented in the current article. Three-dimensional finite element (FE) modeling of the granular material silo is carried out under three-directional earthquake ground acceleration time histories. Granular material is modeled by adopting a continuum approach. The nonlinearity of the granular materials is represented by a hypoplastic material law in the FE approximation. The interface between the granular material and the silo wall is modeled by using surface-to-surface based contact formulation. The horizontal and vertical displacements of the granular material under earthquake ground acceleration at various depths of the silo are studied. Moreover, the stresses induced in the steel silo are also investigated. The static FE simulation and the analytical solution obtained by using Janssen's theory are observed to be in close agreement. Also, the dynamic FE simulations compare with the calculated results using Eurocode 8 part 4 with reasonable accuracy. The stresses in the steel silo wall are higher for loose packing of the granular material as compared to that for the dense packing.

Dynamic FE simulations of buckling process in thin-walled cylindrical metal silos

The buckling of cylindrical steel silos is caused by the wall friction force due to shearing between the silo fill and silo wall. The aim of this paper is to investigate the stability process in a silo composed of thin-walled isotropic plain rolled sheets using a static and dynamic finite element analysis by taking both the geometric and material non-linearity into account during eccentric discharge. Silo shells were subjected to axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. The differences between the results of static and dynamic analyses were comprehensively discussed. The advantages of a dynamic approach were outlined.

Seismic performance of elevated steel silos during Van earthquake, October 23, 2011

Silos are commonly used industrial structures to store dry/granular materials like cement or wheat. A typical silo consists of a vertical steel tank supported by a braced steel frame which rests on concrete support. Due to unloading purposes, the tank is generally located at an elevated position. This makes the structure vulnerable to axial loads in columns due to excessive overturning moments generated at the base of the structure. During the October 23, 2011 Van earthquake in Turkey, many silos collapsed either due to column buckling or foundation problems. In this paper, the field observations regarding the seismic performance of silos after the Van earthquake are first summarized. Then, the seismic performances of two steel-elevated silos located in the earthquake region are studied. One of the silos survived the earthquake by some minor damages in the form of buckling (at bottom horizontal brace) and spalling of concrete support, while the other silo remained undamaged. Nonlinear dynamic time history analyses are performed to evaluate the seismic performances of both silos. As the input ground motion, the recorded ground motion from a temporary aftershock station (about 2 km away from the silos) in the second earthquake is used. Analyses indicate that design and construction quality of elevated silos determine the seismic performance. Finally, recommendations are given to improve the seismic performance of new constructions.

Full-scale tests to measure stresses and vertical displacements in an 18.34 m-diameter agricultural steel silo roof

The large-diameter, metallic, cylindrical silos used in agroindustry require in many cases some type of structure in their uppermost section so that roof panels can be secured in place. These structures often take the form of a lattice of radial and circular beams. The calculation models used in the design of these lattices assume the existence of certain behaviours that are not usually verified experimentally. In the present work, a 3-D beam model was used to predict the stresses and vertical displacements of a metal silo roof structure measuring 18.34m in diameter. To check the validity of the model, these stress and vertical displacement values were experimentally verified at full scale. The instrumentation required to obtain these values in such a large structure is complex and costly. In this study, slings were used to apply load at 54 points in the roof structure, monitored by the use of dynamometers. The vertical displacements and strains suffered by the structure were recorded using fleximeters and strain gauges respectively. The experimental assays showed that the 3-D beam model did not contemplate the true rigidity of the joints between the tension plates and the radial beams at their point of contact with the vertical silo wall. The model therefore required adjustment in order to predict the measured results. The results show the need to use conservative models in the design of these structures.