Silo Wall Research Articles

Study on Effect of Silo Wall Elasticity on Lateral Pressure Ratio

Lateral pressure is a key parameter to silos’ design. It has an important effect on the safety and efficiency of silos. The lateral pressure ratios that recommended by some overseas design codes and literatures have been analyzed. These ratios didn’t take into account the elasticity of silo wall, one of which is 28% smaller than the measure value, but another goes up to super pressure ratio. A new lateral pressure ratio is derived by considering the elasticity of silo wall, which is relevant to Passion ratio of stored material and relative stiffness coefficient . The coefficient of usual metal silo varies from 0.01 to 0.2, so it has significance to consider the wall elasticity.

A simplified analytical procedure for assessing the worst patch load location on circular steel silos with corrugated walls

Silos are widely used in the food and chemical industries for the storage of granular materials. The calculation of their wall dimensions is complicated since the interaction between the stored material and that from which the silo is made is complex, a consequence of their very different mechanical behaviours. The loads exerted on the silo walls by stored materials must be taken into account in silo design, and the means for calculating them is contemplated in Eurocode EN 1991-4. The complexity of the phenomena that occur within silos often leads to the appearance of unexpected and asymmetrically distributed pressures. This is taken into account in the above Eurocode via the concept of the patch load, which is asymmetric and can be exerted at any point on the silo wall. A finite element model has been developed in order to check that the stress resultants derived from the patch load on steel silos with corrugated walls may be predicted by using the well-known expressions of shell theory. Then, a simplified analytical procedure has been developed for predicting the worst location of patch loads for all metal silos, but with special application to corrugated steel silos in Action Assessment Class 3. It has been found that significant differences may be found for most cases with the worst location for the patch load defined in Eurocode for welded silos in Action Assessment Class 2. On the other hand, the values obtained for the maximum meridional membrane stress resultant do not significantly differ, except for high slenderness values in intermediate slenderness silos.

Experimental Investigation of Load Exerted on a Double-Cone Insert and Effect of the Insert on Pressure Along Walls of a Large-Scale Axisymmetrical Silo

Applications of flow aid devices such as inserts improve the silo discharging mode. Considerable effort has been made in finding the best configurations between inserts and silos to achieve optimal functional results. In the present investigation, experiments were carried out to measure the loads imposed on a double-cone insert by particulate solids (free-flowing sand) when it was fitted within an axisymmetrical large-scale silo. Concentric filling/discharging was implemented to carry out such measurements. Pressures along the walls of the silo were also measured. Analyses of the measurement results showed that: (1) the loads on the insert were rather stable in total, but appeared to be asymmetrical at the end of filling; (2) a sudden increase of the loads on the insert was observed at the transition from filling to discharging, but this increase lasted only for a short moment; and (3) the loads on the insert decreased slowly but remained rather high for a large part of the discharge. Effects of the double-cone insert on the pressures along the silo walls were discussed.

Study on Lateral Pressure of Bulk Materials in Silos

With the development of modern industry, silo diameters are bigger and bigger. Lateral pressure of bulk materials in silos is one important parameter for designing silos, which is related to the economy and safety of the structure. However, present calculation methods of the lateral pressure are mostly based on small diameter silos. For now, in the Chinese code the wall pressure computation methods are based on Rankine theory to be calculated. It is shown that the calculated results of Rankine theory may overestimate the pressure. In this paper, the lateral pressure of large diameter silos is studied. A new formula for calculating lateral static pressure on shallow silo wall is derived by static equilibrium method. The formula of this paper is simple of calculation and can be used for large diameter silos with a circular con top pile. The results agree with that of the full-sized silo experiment better than the current code.

Seismic Behavior of Reinforced Concrete Silos Considering Granular Material-Structure Interaction

Silos are structures that are used for storing different types of granular materials. Due to nonlinearity of reinforcedconcrete walls of silo and incrementally nonlinear behavior of granular material, overall seismic behavior of reinforced concrete silos is very complex, in this paper we have used ABAQUS finite element package for modeling of earthquake effect on a reinforced concrete silo, reinforced concrete silo walls are modeled by shell elements and their nonlinear behavior is considered by concrete damaged plasticity model, seismic behavior of granular material inside silo is highly nonlinear and requires a complex nonlinear description of the granular material, the behavior of granular material is incrementally nonlinear even at low strains. The hypoplasticity theory describes the stress rate as a function of stress, strain rate and void ratio. It can model the nonlinear and inelastic behavior of granular materials due to its rate-type formulation. Granular material inside silo is modeled by solid elements and its nonlinear behavior is considered with a hypoplastic constitutive model, for modeling of interaction between silo walls and granular material, surface to surface contact with coulomb friction law is considered between silo walls and granular material. After modeling, the behavior of reinforced concrete silo under earthquake excitation is compared with a model without considering granular material-structure interaction.

THEORETICAL STUDY OF EARTH PRESSURE AT – REST FOR SANDY SOILS

The solution of many foundations - engineering prob lems requires knowledge of the lateral pressure which may be exer ted by the earth or surcharge loads. The lateral earth pressure is a significant design parameter in many of the foundation engineering problems subjected to latera l pressures commonly used as parts of many civil engineering projects. S ome examples of these structures are, retaining walls, sheet-pile walls, both braced and unbraced excavations, trench excavations, grain pressures on silo walls, cofferdams, caissons, embedded shells and other types of underg round structures requiring an estimation of the lateral pressure fo r design or stability analysis. The different formulae such as Jaky , Hendron , Br ooker and Ireland, Vierzbiczky , Saglamer , Wenkow , Robert Szepesh azi , Matsuoka et al, Bolton , and others were used to determine the fact or Ko. The main aim of this research is to estimate the co efficient of earth pressure at rest equation depending on the theoreti cal relationship between the active, passive earth pressures and the lateral strain of soil. The important result from this research is: ) sin 1 /( ) sin 1 ( 2 2 φ φ + = o K

Otimização Estrutural das Paredes de Silos Metálicos Prismáticos com a Utilização do MS Excel Solver.

The aim of this work is to present the application of Microsoft Excel Solver to the optimization of stiffened walls of metallic prismatic silos, profiled in trapezoidal and zigzag sections, seeking the construction of an auxiliary tool to structural designers. Some numerical results are presented in order illustrate the use of Solver, as well as to show the significant economy achieved with to the developed formulation.

Discrete element modelling of grain flow in a planar silo: influence of simulation parameters

There is extensive engineering literature concerning the prediction of pressure and flow in a silo. The great majority of them are based on continuum theories. The friction between the stored material and the silo wall as well as the inclination of the hopper at its base are considered to be the most influential parameters for the flow pattern within the silo. In this paper, the filling and discharge of a planar silo with a hopper at its base has been modelled using DEM. The aim is to investigate the influence of DEM model parameters on the predicted flow pattern in the silo. The parametric investigation particularly focused on the hopper angle of inclination and the contact friction between particles and walls. The shape of the particles was also considered by comparing spherical and non-spherical particles, thus providing an insight into how particle interlocking might influence solids flow behaviour in silos. The DEM computations were analysed to evaluate the velocity profiles at different levels as well as the wall pressure distribution at different stages during filling and discharge. A detailed comparison reveals several key observations including the importance of particle interlocking to predict a flow pattern that is similar to the ones observed in real silos.

Design Force Estimation Using Artificial Neural Network for Groups of Four Cylindrical Silos

The computation of design forces for the reinforced concrete groups of four cylindrical silos (GFCS) is fairly difficult because of the continuity of the walls between the adjacent silos. In this study, the efficiency of the artificial neural network (ANN) in predicting the design forces and the design moments of the GFCS due to interstice and internal loadings was investigated. Previously obtained finite element (FE) analyses results in the literature were used to train and test the ANN models. Each parameter (silo wall thickness, intersection wall thickness and the central angle spanning the intersection walls of the GFCS) affecting design forces and moments was set to be an input vector. The outputs of the ANN models would be the bending moments, hoop forces and shear forces at the supports and crowns of the interstice walls due to interstice loadings; the maximum axial forces and maximum bending moments at the external walls due to internal loadings. All the outputs of the ANN models were trained and tested by three-layered 11 back-propagation methods widely used in the literature. The obtained results presented that these 11 different methods were capable of predicting the design forces and the design moments at the interstice and external walls of the GFCS used in the training and testing phases of the study.

The relationship of silage temperature with the microbiological status of the face of corn silage bunkers

A method is proposed to quantify aerobic deterioration of corn silage forage quality as related to the temperature of silage mass in the bunker. Aerobic deterioration, apart from causing nutritional value losses, affects the hygienic quality of silages through the accumulation of pathogenic organisms and their toxins. A survey was carried out in northern Italy that involved a detailed examination of silage bunker from each of 54 dairy farms. Samples from the core, the peripheral areas within 1m from the silo walls, and the molded spots, when present, were collected. The sample and silage temperatures across the working face were measured at depths of 200mm at 11 locations and at 7 elevations. The temperature of the central zone of the silo was defined as the reference temperature (Tref40). The difference between the temperature of the silage sample and the Tref40 was used as a heating index associated with aerobic deterioration (dTref40). The working face area with visible molds was measured. The samples were analyzed for DM content; pH; water activity; nitrates; lactic, acetic, and butyric acids; and microbiological count of yeasts, molds, and clostridia spores. The core samples always showed a pH below 4.0 and a dTref40 below 2°C, whereas the silages from the peripheral areas were split into 2 groups, one that had a pH lower than 4 and a dTref40 lower than 3.5°C (53%) and one that had a pH higher than 4 and a dTref40 higher than 5°C (47%). Most of the silages from the peripheral areas (94%) and all the silages from the moldy spots that have a dTref40 above 5°C had a pH higher than 4.5. Furthermore, a positive dTref40 higher than 5°C corresponds to a higher yeast count than 5 log cfu/g in most of the silages from the peripheral areas (93% of samples) and in almost all the silages from the molded spots. The evaluation of the extension of the visible molded areas combined with temperature measurement at 200mm behind the feed-out face could offer a good indication of the health status of silage during consumption. Furthermore, this method could be useful to detect early stages of the aerobic deterioration process and to improve silage management.

Effect of the ratios of diameter of silo to bead on the pressure screening in granular columns

We present the apparent mass measurements at the bottom of granular packings for different bead and silo sizes. The redirection parameter K in Janssen theory is found to increase with the ratios of the diameter of the silo to the bead. We attribute this feature to the friction between the beads and the confining wall of silo; it is the role of friction that leads to variations in the shielding of vertical stresses as well as pressure screening.

Pressure measurements in steel silos with eccentric hoppers

It is known that concentric filling and discharge are the most recommended solutions in silo design. However, different reasons such as costs, space problems and the client's specific requirements have a significant influence on the final design. Therefore, engineers sometimes need to make use of eccentric filling and discharge solutions. These designs are usually related to phenomena such as unfavorable switches in the flow regime, associated with extreme unsymmetrical pressure distributions around the silo wall, oscillations of the load, etc., which may cause failures or instabilities of silo structures, involving then high costs for the industry and, in the worst cases, accidents where human life may be endangered. Understanding about these phenomena associated with hopper eccentricities is still needed. This research work deals with pressure measurements on three steel silos with different hopper eccentricities. The results not only confirm, at a qualitative level, phenomena that have also been described in previous research, but also provide new knowledge concerning non-symmetric loads in wheat and maize silos with conical hoppers of different eccentricities. Non-symmetric components of the pressures and shifts in flow regimes have been studied and discussed in relation to load assessment for the design of silos.

On the use of plate-type normal pressure cells in silos: Part 1: Calibration and evaluation

Pressure cells are measuring devices commonly used in silo research to study loads exerted by a granular material stored against a silo wall. The design of normal pressure cells for use in an experimental silo research project is critical, mainly because measuring errors complicate the interpretation of results. Once the cells have been delivered from the manufacturer to the researcher, they should be calibrated and validated with reference to the measurement of pressure from a granular material against a silo wall. Two related papers deal with a specific plate-type normal pressure cell for use in an installation of three full-scale steel silos with different hopper eccentricities (concentric, half-eccentric and full-eccentric) as part of a silo research project. It was found to be necessary to validate the performance of the cells when measuring pressures in the silos in order to arrive at a solid basis for the interpretation of the pressure measurements in the silo installation aforementioned. This paper presents calibration results from three investigated methods as well as results from a finite element analysis of the plate deflection of the pressure cell which were performed to evaluate the non-linear behaviour of the signal from the cell. Results suggested that the air-pressure calibration method turned out to be the most suitable in this particular case, that a lack of stiffness of the plate cell was revealed and that its boundary constraint conditions were not stable. Amendments were proposed in order to improve the accuracy of measurements. Furthermore, the knowledge acquired from the study of these plate-type cells constitutes the basis of recommendations for another design of pressure cells for which the calibration as well as the interpretations of test results would become simpler.

On the use of plate-type normal pressure cells in silos: Part 2: Validation for pressure measurements

This paper deals with a specific plate-type normal pressure cell to be used in the study of loads in silos. An evaluation of the pressure cells and their installation in a silo wall revealed the need for a validation of their performance when measuring pressures in silos. The pressure cells were mounted along a vertical line of the wall of the silo with a concentric hopper in order to be able to measure pressure distributions, which may be considered well-known, especially during the filling processes. Tests were carried out with two commonly stored agricultural granular materials: wheat and maize. Analyses based on a Discrete Element Model were performed to contribute to the validation. The result of the validation was that measuring errors should be expected and that the measuring errors changed with the stiffness of the stored material and therefore with the flow conditions. This knowledge is essential for a later proper interpretation of pressure measurements in test silos.

On the steel cost of circular flat-bottomed silos designed using the Eurocodes

Nowadays, Eurocodes have become the reference standards for silo design within the European Union. They include new procedures for load assessment and structural verifications aiming to design safer silos. However, many silo manufacturers are still reluctant to use them (or at least all their prescriptions) because of the loss of competitiveness they are experiencing in comparison with former standards. This paper shows how steel cost of flat-bottomed circular silos varies when different silo geometries and stored materials are considered. The influence of critical structural verifications on steel costs, such as buckling of the silo wall, were also analyzed and some conclusions and practical recommendations for silo designers were proposed.

Study of Buckling in Steel Silos under Eccentric Discharge Flows of Stored Solids

The most serious loading condition for slender thin-walled metal silos has long been recognized to be the condition of discharge, with eccentric discharge causing more catastrophic failures than any other. Two key reasons for this high failure rate are the difficulties in characterizing the pressure distribution caused by eccentric solids flow, and in understanding the associated unsymmetrical stresses in the silo wall. Few studies have addressed either the linear elastic behavior of such a silo or its buckling failure under eccentric discharge. In this study, the eccentric discharge pressures are characterized using the new rules of the European Standard EN 1991-4 on Silos and Tanks. This novel description of unsymmetrical pressures permits a study of the structural behavior leading to buckling during eccentric discharge, including the critical effects of change of geometry and imperfection sensitivity, to be undertaken using geometrically and materially nonlinear computational analyses. The mechanics of...

Experimental and theoretical investigations of silo music

This paper deals with strong dynamic effects connected with booming sound (called silo music) appearing during confined granular flow in silos. Novel experimental data have been gained through Electrical Capacitance Tomography (ECT) and an extraction of operational deflection shapes. A dynamic plane strain FE model of the granular material and oscillating wall was presented. The numerical results support the key role of dynamic coupling between silo wall oscillations and dynamics of the flowing material induced by a change of a flow direction at the transition zone between cylindrical and converging flow.

Modeling of shear localization during confined granular flow in silos within non-local hypoplasticity

The paper deals with multiple shear zones in the interior of cohesionless granular bodies during plane strain quasi-static granular flow with controlled outlet velocity in experimental silos. The finite element calculations were carried out with a hypoplastic constitutive model enhanced by a characteristic length of micro-structure by means of a non-local theory to obtain mesh-independent results. The constitutive model can reproduce the essential features of granular materials during shear localization. FE analyses were performed with the help of an Arbitrary Lagrangian–Eulerian formulation using an explicit time integration approach for experimental silos containing initially dense dry cohesionless sand. Silo walls were assumed to be very rough or smooth. Emphasis was given to the propagation of multiple shear zones in the interior of flowing sand. The numerical results were compared with corresponding experimental tests.

Powder Static Pressure Distributing on Pyramidal Silo

Based on the assumptions of Janssen formula, the powder static pressure distribution is discussed and the analytical formulas are established. The relevant numerical study is fulfilled through finite element contact analysis. Through comparing the finite element analysis results with the analytical results, it shows that the analytical formulas have error. The reason is mainly that the special contact state formed by the special silo structure is not incarnated in the analytical formulas. Based on the finite element analysis result, the analytical results are amended to give the final formulas of contact pressure on the pyramidal silo. The formulas show that the contact pressure correlates with the attribute parameters such as silo material, loose material bulk density and internal friction angle, as well as the design parameters such as silo wall obliquity and silo height. The final formulas are programmed to implement pressure load by using ANSYS parametric design language. The load distribution graphs are consistent with the scatter diagram, and the loading languages have good generality and portability. The formulas can simplify relevant calculation, and may be regarded as a supplement of Janssen formula.

Strengthening metallic cylindrical shells against elephant's foot buckling with FRP

Thin metal cylindrical shell structures such as silos and tanks are susceptible to an elastic–plastic instability failure at the base boundary known as elephant's foot buckling, due to its characteristic deformed shape. This form of buckling occurs under high internal pressure accompanied by axial compression in the shell structure. This is a common failure mode for tanks under earthquake loading. Another common situation is in a silo where the silo wall is subjected to both normal pressures from the stored granular solid and vertical compressive forces developed from the friction between the stored solid and the silo wall. This paper presents a novel method of strengthening cylindrical shells against elephant's foot buckling in which a small amount of fibre-reinforced polymer (FRP) composite, used at a critical location, can effectively eliminate the problem and increase the buckling strength. The strengthened shell is analysed using linear elastic bending theory in this preliminary study. Within the scope of this research, the strengthening effect is shown to be sensitive to the thickness, height and location of the FRP sheet. The issue of optimal FRP strengthening to allow the shell to attain pure membrane-state deformation is examined in detail as strengthening with too much and too little FRP are both undesirable. Both pinned-based and fixed-based shells are examined and their responses are compared.