Design Of Silos Research Articles

Effect of Microscopic Properties on Flow Behavior of Industrial Cohesive Powder

The characteristics of powders on a bulk scale are heavily influenced by both the material properties and the size of their primary particles. Throughout the stages of storage and transportation in the powder processing industry, various forms of deformation and stress, such as pressure and shear, impact these materials. Recognizing the point at which a powder undergoes yielding becomes particularly significant in numerous applications. There are also times when the level of stress needed to maintain it must be understood. The measurement of powder yield and flow properties remains a challenge and is addressed in this study. As part of the European collaborative project, a number of shear experiments were performed using two shearing devices: the Schulze ring shearing device and the Anton Paar Powder Cell (APCC). These experiments have three purposes: (i) test reproducibility/consistency between two shear devices and test protocols; (ii) relate bulk behavior to microscopic particle properties, focusing on bulk density and thus the effect of cohesion between particles; and (iii) investigate the influence of the temperature of heated powders on the powder’s flow properties, which is important for industrial reactors. Interestingly, for samples with small particle sizes, bulk cohesion increases slightly, but bulk friction increases significantly because of particle interaction effects. The experimental data not only provide useful insight into the role of microscopically attractive van der Waals gravitational and/or compressive forces on the macroscopic flow behavior of bulk powders but also have industrial relevance. We also provide robust data of cohesive and attritional fine powder for silo design used for calibration and validation of silos, models, and computer simulations.

Measurement of acceleration and angular velocity of particles during a 3D silo discharge

Accurate measurement of the three-dimensional (3D) movement of discrete particles is crucial for comprehending complex granular rheology in silos. In this paper, the acceleration and angular velocity of particles in 3D silos are measured by using a spherical detector based on inertial technology and magnetic positioning technology. The acceleration of particles is the largest in the center of silos, which suggest that the resistance generated by friction and extrusion is the smallest. Surprisingly, the angular velocity distribution follows lognormal function except for particles near the outlet. The correlation between acceleration and angular velocity is opposite in different flow regions. It reveals for the first time that the extent to which the resultant force on the particles affects their rotational motion is related to the flow pattern. These results have practical significance for regulating the granular flow pattern and optimizing the structural design of silos.

Current design of rectangular steel silos: limitations and improvement

This study proposes a modification for the current design approach for square and rectangular silos that accounts for silos’ wall flexibility. First, the authors investigated the effect of wall stiffness symbolized by the wall width-to-thickness ratio (a/t) and silo’s dimensions, on the wall-filling pressure using a recently validated 3D finite element model (FEM). The model was then employed to predict the pressures acting on silos’ walls accounting for the stress state in stored granular materials. Most design formulas and guidelines assume silos’ walls to be rigid. This assumption is acceptable for the case of rigid wall concrete silos; however, it is questionable for semi-rigid, flexible wall metal silos. Consequentially, it is crucial to determine the minimum wall stiffness necessary to secure the applicability of the current design rigid wall assumptions and to propose a way to deal with semi-rigid and flexible walls. To this end, several wall pressure distributions that correspond to filling steel silos with varied wall thicknesses were studied. A new adjustment to the Janssen technique was proposed for a better estimate of the wall-filling pressures for square and rectangular silos. In the case of prismatic silos, the Eurocode uses the Janssen equation together with an equivalent radius of a corresponding circular silo (with the same hydraulic radius) to determine the wall pressure. This method predicts pressure values that are practically accurate for rigid-wall silos, but its accuracy decreases for semi-rigid and flexible-wall silos. As an enhancement, the Janssen equation was modified in this research to generate more accurate pressure estimates based on the equivalent volume concept. The finite element results of several developed models with the same granular material were compared to the estimations of the newly established approach to verify the broad range of its applicability.

The role of particle size and other properties on silo discharge behaviour of chipped wood biomass

To achieve net-zero carbon emissions by 2050, the UK government emphasizes the pivotal role of sustainable bioenergy in electricity, transportation, and heating. However, challenges persist in handling biomass particulate solids in production facilities, leading to economic impacts. This study investigates the flow characteristics of stemwood chips from four tree species using a novel drum chipper. Experimental analyses include bulk density measurements, silo discharge studies, biomass flow property assessments, and wall friction measurements. Comparative analyses are performed using Jenike's procedure for building wedge-shaped silos, with a focus on predicting the critical opening size to prevent arching. Additionally, the paper delves into the creation of statistical models aimed at identifying key factors influencing the flow behaviour during silo discharge. Emphasis is placed on understanding potential discrepancies between theoretical predictions and experimental results concerning critical silo openings for arch-free discharge. The results contribute to understanding the factors influencing the flow behaviour of wood chips, informing silo design considerations. Our findings suggest limitations in applying traditional silo design methods, urging further research for more accurate predictions.

Effect of bevelled silo outlet in the flow rate during discharge

We investigate the effect of a bevelled (or slanted) outlet on the discharge rate of mono-sized spheres from a quasi-two-dimensional silo, using the discrete element method. In contrast to hopper discharges, where the bevelling is across the entire base of the container, we study a bevelled opening that is significantly smaller than the silo width and in which the slanting is limited to half a sphere diameter at the boundary of the outlet. We show that the bevelling increases the flow rate comparably to the inclination in hopper walls. Using Beverloo’s model, we relate this increase in rate to what we define as the ‘effective opening’ of the silo and analyse the velocity profiles associated with the discharges. We show that different openings, having effectively the same discharge rates, give rise to distinctly different internal dynamics in the silo. These results have the potential to aid industrial processes by fine-tuning and improving control of silo discharges, with a minimal impact on silo design, thus significantly reducing production and handling costs.

ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ СТІНКИ СТАЛЕВОГО СПІРАЛЬНО-ФАЛЬЦЕВОГО СИЛОСУ

In the context of martial law, Ukraine's agricultural sector is suffering significant losses. By May 2022. Ukraine has already lost almost 13 million tonnes of elevator capacity, some of the grain warehouses have been completely destroyed, and some are in the occupied territories. In this regard, there is a need for elevator capacities, namely, prefabricated, cost-efficient storage capacities. Such structures are exemplified by silos. There are many design solutions for metal silos. However, the rising cost of materials is causing a need to reduce the material intensity of the structure, which is encouraging cylindrical silo manufacturers to search for new types of shell construction. An innovative design of lightweight, industrial silos is a metal spiral-fold silo. The article describes the design of steel spiral-fold silos. The specifics of the spiral-fold silo design, which affects their stress-strain state, are analysed. The characteristics of the silo that was used as a source of samples for the experiment are given. The samples and equipment for the experimental study of a wall of a metal spiral-fold silo are considered. The stages of the experiment are described. The loading of the samples was performed by a central bending load applied in a static mode in the range from 0 kN to 5.5 kN. To determine the relative strains, the structure was unloaded after each loading stage. The analysis of the sample's relative strains which were measured by AVD-4 is made. The character of interaction and deformation of the wall with the folding lock is revealed. The degree of the folding lock opening was estimated. The character of work of the wall and the folding lock in the limit and non-limit states is obtained. A comparison of experimental results with finite element analysis in the LIRA-SAPR software package was performed. The conclusion about the reliable operation of the wall of a spiral-fold silo under operational and increased loads is substantiated

DESIGN OF TRANSITION JUNCTIONS OF SILOS’ CONICAL HOPPERS ACCORDING TO EUROPEAN STANDARD EUROCODE

Problem statement. Today, the food security of the world is one of the main issues for the political, economic and scientific community, and the recent crisis with the export of Ukrainian grain only intensifies the urgency of the problem. The important part of this issue is creation of reliable and safe grain storage silos. An analysis of recent accidents in silos, especially with conical hoppers, revealed a range of imperfections in outdated regulatory practices that Ukraine inherited from the Soviet building norm system. A limited list of agricultural crops, ignoring the statistical spread of their physical and mechanical characteristics, not differentiating between the stress-strain state for filling and discharge silos, the absolute absence of guidelines and recommendations for the design of principal connections - this is a far from complete list of shortcomings and omissions of outdated Soviet standards. With the entry into force of the new Ukrainian norm DBN V.2.6-221:2021 “Designs of steel silos with a corrugated wall for grain”, the situation should have changed. Firstly, the new standards take into account the world experience in design, construction and fabrication of silos, and secondly, they have a direct and legitimate reference to the necessary standards of the Eurocode system, in which a modern engineer can find answers to a wide range of practical questions. Unfortunately, the introduction of this, without exaggeration, modern and extremely important standard into construction practice is constantly ignored. On the one hand, this is due to the unwillingness of Ukrainian manufacturers to switch to new European and more rigid requirements for reliability and safety, on the other hand, the fear of Ukrainian engineers in front of the complex and extensive Eurocode standardization system. The purpose of the article (ignoring the financial commercialism of individual silo manufacturers) is explain to domestic designers a few provisions of the new DBN V.2.6-221:2021 related to the design of silos with a conical hopper. In particular, the design of one of the very important units at the point of transition of the cylindrical part of the silo to the conical hopper. Methodology. For this, the general ideology and methodology of the limit state method, implemented in the Eurocode standards through the system of partial reliability factors, as well as classical methods of structural mechanics, which are still not reflected in the system of building regulation of modern Ukraine, are used. Results. As a result, clear recommendations for the design of the transition junction of silos with a conical hopper in accordance with Eurocode and DBN V.2.6-221:2021, as well as clarification of “special” points that are not properly covered in both regulations. Conclusion. The recommendations and explanations given in the article, firstly, accelerate the introduction of the new DBN V.2.6-221:2021 into engineering practice, which is harmonized with the Eurocode system, and secondly, allow to achieve more reliable and safe design solutions in the field of silos fabrication, in thirdly, they deactivate the chronic design fear of Ukrainian engineer before the European school of building standards.

Analysis and design of silos by the post-tensioned method

This design focuses on the analysis and design of silos exercising the post-tensioned system, aiming to facilitate these critical storehouse structure’s structural effectiveness and safety. Silos are extensively used in colourful diligence to store bulk accoutrements, and their structural integrity is of consummate significance to ensure dependable and secure operations. The study involves a relative analysis between conventional silo designs and those employing the post-tensioned system. The geste of silos under different loading conditions is simulated and evaluated. The assessment considers key performance indicators such as load-bearing capacities, deflection, cracking behavior, and overall stability. The findings indicate that post-tensioning significantly enhances the structural performance of silos. The post-tensioned method offers a sustainable and cost-effective alternative to traditional silo construction by reducing cracking and improving overall stability. The results contribute valuable insights to the optimization of silo design, offering engineers and stakeholders in the industry a practical and efficient solution for industrial storage requirements. In conclusion, the analysis and design of silos using post-tensioning techniques provide a promising approach to enhancing the effectiveness and safety of silo structures. Implementing these innovative methods can improve performance and reduce maintenance costs, making them an attractive option for future silo construction systems.

Seismic Design of Elevated Silos and Tanks – a Study on Behaviour Factors

AbstractAccording to EN 1998‐4:2006 3.4 (4), elevated silos may be designed considering medium or high ductility class for the support structure, abbreviated DCM and DCH respectively, for which an overall behaviour factor q greater than 1,5 may be assumed.Undoubtedly, when a silo or tank supported by a sway frame or a vessel with integrated legs is considered, it is expected that plasticity will be induced due to the overall system's performance and thus, motion amplitudes will be reduced due to energy dissipation. However, the shell upper‐structure is a very thin‐walled class 4 cross section. Hence, it might fail due to buckling at much smaller motion amplitudes (corresponding to acceleration amplitudes) than those, which the support structure can follow without failing.Therefore, from the authors' point of view it is not sufficient to settle with a single behaviour factor for the overall structural system. Alternatively, a two‐step approach is recommended: With this two‐step approach it can be verified, that (sudden) buckling of the shell does not happen prior to the introduction of plasticity at the sub‐structure and in extension to the desired energy dissipation.The proposed two‐step approach is demonstrated by suitable examples with a different range of parameters. Therewith, it will be shown that the assumption of q = 1,5 for elevated silos or tanks can be unsafe. An improvement of the current EC8‐4 rules is proposed in order to enable a practical, safer and more efficient design procedure.

Performance-Based Code Calibration and Total Probability of Failure of the Nuclear Containment Structure Subjected to Missile Impact

The multifarious calamities upon nuclear containment structures (NCS) and insufficient reliability-based factors inspired the current study for the investigation of hard missile impact. Available codes for design and construction of NCS suggest a load factor of 1.0 and basic information for the missile impact scenarios. However, the current study proposes novel reliability-based load and resistance factors for NCS subjected to a hard missile impact. The performance-based probabilistic energy capacity and demand models have been used for the code calibration process. These models were based on three performance levels associated with four levels of damage. The levels were chosen based on local damage due to its rigidity from insignificant penetration to complete perforation of the missile. This study also developed hazard curves for various distributions of missile mass and velocity. The total probability of failure of NCS was calculated based on a realistic range of material and geometrical variables and globally existing cruise missiles, wind-borne missiles, pressure pipes, iron rods, and others. The current investigation considers all the inherent uncertainties of target and missile. This study circumvents the limitations and develops performance-based load and resistance factors based on probabilistic models. The developed load and resistance factors for codal provisions are tied in turn to the different performance levels of the NCS. These factors can be used for the design of NCS, bunkers, silos, storage tanks, slabs, and others without performing exhaustive analysis and/or experiments.

Flow properties for silo design - a review

Silos are essential structures to maintain the quality of products such as grains, seeds and other agricole products used by industries, agricultural, and mineral sectors. The correct dimensioning and design of a silo project depends on determining the physical and mechanical properties of the products to be stored, since the type of flow as well as the intensity and distribution of stresses in the structure depend on these. There-fore, product characterization should be one of the first steps taken when designing or modifying a loading and unloading system. The characterization of the product to be stored consists of determining its physical properties, such as: consolidated specific weight, internal friction angle, effective internal friction angle, friction angle of the product with the wall, flow function, granulometry, and moisture and product content, which must be carried out under the most severe conditions that can occur in the silo. The Jenike Shear Test device is suitable equipment to measure these properties, making it possible to determine the stresses that the product will be subjected to during storage and in the flow conditions predicted to happen in the silo. There-fore, this review aimed to approach the physical and flow properties of stored products, enabling the development of safe, robust and reliable projects, in such a way that operations such as unloading, transilage, dosing, and packaging of products can be maximized. The importance of each property is noted, as it intrinsically affects the behavior of the product during storage, handling and processing.

ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ЕЛЕМЕНТІВ КОНСТРУКЦІЇ МЕТАЛЕВИХ СПІРАЛЬНО-ФАЛЬЦЕВИХ СИЛОСІВ

Metal capacities for the storage bulk materials are became widespread every year. The design of the steel spiral-fold silos and the peculiarities of the folding lock are considered in the article. The elements of the rigidity system of prefabricated metal silos from corrugated panels on bolted joints are given.

Flow profile and wall normal stress characteristics in pattern-transformable flow silos

This paper describes an experimental investigation on the flow profile and wall normal stress characteristics in pattern-transformable flow silos, where the flow pattern changes from the funnel flow to the mass flow during discharge. The flow zone evolutions in this kind of silo are observed and discussed. The applicability of the existing funnel flow zone prediction model to this flow type is accessed. The distributions and dynamic characteristics of the wall normal stresses are obtained and analyzed. The reasons for the overpressure decrease and stress fluctuation weakening in pattern-transformable flow silos are discussed. A method to calculate the forces acting on the stagnant zone is proposed, and the force analysis is made at the moment when the flow pattern transforms. The unbalance of forces acting on the stagnant zone as a whole plays an important role in the flow pattern transformation. The findings offer a possibility to improve the pattern-transformable flow silo design.

Axial buckling of imperfect cylindrical steel silos with isotropic walls under stored solids loads: FE analyses versus Eurocode provisions

Stored solids loads on silo vertical walls are composed of two orthogonal components: the horizontal component that internally pressurizes the silo and the vertical wall frictional component that causes axial compression. For an imperfect cylinder, the elastic axial buckling resistance may be considerably raised by a uniform internal pressure as it alleviates the detrimental effect of the geometrical imperfections. However, at high internal pressures, the combination of axial compression and circumferential tension may result into a plastic instability that is commonly termed elephant’s foot buckling. Both stabilizing and destabilizing effects of internal pressure are taken into account by EN 1993–4-1 in the buckling stress design of steel silos with isotropic walls under axial compression. In this paper, using non-linear Finite Element (FE) analyses, the effects of internal pressure on axial buckling of steel silos have been fully investigated and the Eurocode provisions on this issue have been thoroughly examined.

Active Earth Pressure Acting on Circular Shafts Using Numerical Approach

Retaining walls in axi-symmetric conditions and in plane strains have been widely treated in the literature using different approaches (limit equilibrium, limit analysis, slip line, and numerical techniques by finite elements or finite differences). The finite element or finite difference method provides more accurate solutions to the problem than the limit equilibrium method. In this paper, a new model of retaining wall in the axi-symmetry conditions under outward pressure is considered, this case can be widely used in the design of grain silos, buildings and road constructions. Numerical calculations using FLAC are reported to evaluate the evolution of the earth pressure distribution on a cylindrical wall filled with granular material and subjected to radial displacement. A parametric study is carried out in order to evaluate the distribution of the active earth pressure on the wall according to the radius, the angle of friction of the granular material, and the angle of friction of the interface granular material-wall. This study shows that there is an effect of the circular shape and the inclination of the wall on the active earth pressures. Doi: 10.28991/CEJ-2022-08-04-09 Full Text: PDF

The ‘miniature silo’ test: A simple experimental setup to estimate the effective friction coefficient between the granular solid and a horizontally-corrugated cylindrical metal silo wall

Corrugated walls are widely employed in the construction of metal silos. Despite the long history of testing to establish bulk material parameters for silo design, there does not appear to be an established test procedure to directly determine the effective friction coefficient for a corrugated wall other than an adaptation of a classical direct shear test. EN 1991-4: 2006 prescribes a simple weighted average formula for this coefficient based on the internal friction angle of the granular solid and a ‘flat’ wall friction coefficient. This paper describes a set of miniature-scale silo tests performed at the University of Bologna intended to establish a simple but useful procedure to directly estimate an average global friction coefficient between the granular solid and a corrugated silo wall. These ‘miniature silo’ tests are simple enough to be performed in any civil engineering laboratory with standard equipment. • Particle-wall friction coefficient is fundamental for structural design of silos. • No tests are available to measure the effective friction for a corrugated wall. • A novel straightforward experimental test is proposed to fill this gap. • The miniature-silo test can be built using basic tools easy to be found in any lab. • The obtained results are in accordance with EN-1991-4 average formula predictions.

Comprehensive Review on the Dynamic and Seismic Behavior of Flat-Bottom Cylindrical Silos Filled With Granular Material

The seismic design of industrial flat-bottom ground-supported silos filled with granular material still presents several challenges to be addressed. They are related to the main aspects which differentiate silo structures containing granular material from other civil structural typologies: 1) the relatively low silo structure mass as compared to the ensiled content mass; 2) the granular nature of the ensiled material. Indeed, the internal actions in the structural members are governed by the complex dynamic interactions along the interfaces between granular content and silo wall or base, or even the internal interaction between particles. More in detail, even though the scientific interest in such complex interactions dates back to the middle of the 19th century, several issues are still unclear such as the dependency of the fundamental dynamic properties (period of vibration and damping ratio) on the characteristics of the dynamic excitation (intensity, frequency content, duration) or the amount of ensiled material mass activated during a seismic excitation and provoking extra pressures on the wall (effective mass). Therefore, most of current seismic code provisions for silos are grounded on rather approximate and simplified assumptions leading to often over-conservative evaluations. The present paper intends to provide a comprehensive summary of the mainly acknowledged experimental and theoretical advances in the dynamic and seismic behavior of silos, supporting the potential researcher in the field to understand the real differences between the code assumptions and recommendations and the actual conditions, as well as illustrating the open issues to be still further investigated.

Ejector Function Method for Flowfield Analysis of Silo

Aiming at the problem of silo design, the silo ejector model and ejector function were proposed. The properties of the static pressure matching function were studied. The critical conditions were analyzed when the engine total pressure, the diameter of the silo, and the outlet pressure of the mixing chamber changed. It is proved that the curve that shows the inlet pressure of the mixing chamber changes along with the outlet pressure of the mixing chamber is a straight line parallel to the horizontal axis when the outlet pressure of the mixing chamber is smaller than the stagnation critical point, the curve that shows the inlet pressure of the mixing chamber changes along with the total pressure of the nozzle develops along the optimal pressure function curve when the total pressure of the nozzle is greater than the stagnation critical point, and the curve that shows the inlet pressure of the mixing chamber changes along with the diameter of the mixing chamber develops along the optimal pressure function curve when the diameter of the mixing chamber is smaller than the stagnation critical point. The characteristic curves of the silo ejector and the ideal ejector were compared when imbalance or wall friction were of concern, respectively, which show that the degree of imbalance has little effect on the calculation results of the silo ejector and the wall friction has a significant effect, especially near the stagnation point. The results provide important guidance for the design of silos and ejectors. Finally, the reliability of the ejector function method is verified by comparing the experimental data with the theoretical results.

ASSESSMENT OF CARRYING CAPACITY OF THE ROUND IN PLAN REINFORCED CONCRETE FOUNDATION FOR THE SILO

During the design, installation and operation of silos, they have defects and damage of various kinds, which affect the stress-strain state and durability of structural elements. Timely inspections and determination of technical conditions of structural elements of the structure and the site as a whole, will establish the possibility of its further safe operation or the need to restore operational properties by ensuring structural safety and reliability of structures. Therefore, the development of design schemes, methods of calculating the stress-strain state, life expectancy and further reinforcement for round reinforced concrete elements of silos with local damage, is quite relevant. Improper maintenance and operation of structural elements, as well as errors in the design and installation in the future lead to unusable for normal operation and sometimes an emergency. The development of projects to strengthen existing structures is a very responsible matter. The most common solution for strengthening existing foundations is to increase the area of support of the foundation cushion, which is not always possible in a compact building. The purpose of the work is to determine the technical condition of the building structures of the silo and the results of calculations performed in the PC Lira, to offer options for strengthening the foundation on a specific example. Structural solutions of the reinforced concrete monolithic foundation of the silo, the main defects and damages determined by the technical condition of the structure are given. For further safe operation of the structure, it is recommended to reinforce the wall foundations by gluing composite tapes and perform reinforcement of the foundations by controlling the growth of piles in accordance with the additional working design of the structure reinforcement. If the latest recommendations on strengthening and adhering to the safe and reliable operation of construction and structures are followed, further operation of building structures will be safe.

Investigations of the hot granular material effect on steel silo

When the hot granular material is placed in a steel silo, there will be significant thermal effects on bending moment, shear force and stress of the silo wall. But there is no feasible method to identify the stress and deformation of the silo with hot granular material. To fill this gap, this paper proposes an analytical method based on the cylindrical shell theory. A case study is performed to demonstrate the accuracy and feasibility of the analytical method. The results show that the proposed method produces satisfactory results when comparing with the finite element method. Besides, it can be seen from the analysis that large radial displacement occurs in the middle height of the silo wall when the hot granular material is placed in. Afterwards, the parametric studies are conducted to investigate the structural behaviors of the silo under different conditions that produces useful information for considering thermal effects in silo design. The research findings show that the length of the transition zone, the vertical temperature differential and the ratio of radius to thickness significantly influence the thermal stresses, which should be paid attention to in practical engineering design.