Vertical Loads Due to Wheat on Obstructions Located on the Floor of a Model Bin

Tests were conducted in a model grain bin to evaluate the vertical loads acting on differently shaped obstructions embedded in wheat during filling, detention, and discharge. The bin had corrugated galvanized steel walls with a 1.83 m diameter and a flat bottom. All tests were conducted in a bin that was centrically loaded and unloaded. Three differently shaped obstructions (disc, cone, and cylinder) were tested; each had a circular base equivalent to 6% of the bin floor area. The obstructions were supported in the bin using a three-legged support structure. Each leg of the support structure rested on a load cell attached to the bin floor. Tests were conducted with the obstructions located in the bin at three different eccentricity ratios (ratio of the centerline of the obstruction to the bin radius, ER = 0, 0.5, and 0.67) and at two different grain heights (height of grain depth to bin diameter ratio, H/D = 0.4 and 0.75). The radial distribution of vertical pressures in the bin varied, with the highest pressure in the center of the bin and the lowest at the bin wall. The largest vertical load on the disc and cone obstructions was measured at the end of filling. The largest load on the cylindrical obstruction was observed immediately after the initiation of bin discharge. At the end of filling and detention, the vertical loads on the disc, cone, and cylinder were 4.8, 3.7, and 4.9 kN, respectively, for obstructions located at ER = 0 and H/D = 0.4. At a location closest to the bin wall (ER = 0.67), the vertical loading on the disc, cone, and cylinder were 4.4, 3.4, and 4.4 kN, respectively. The greatest difference in vertical loading between the location and type of obstruction was on the order of 50%. Bending moments were also observed to act on these obstructions. Bending moments at ER = 0.67 were much larger than those determined at ER = 0.5. For the disc and cone, moments at ER = 0.67 were three times as large as those determined for tests conducted at ER = 0.0. At the onset of discharge, the vertical loading on both the disc and cone decreased significantly, while the vertical loading on the cylinder increased significantly. Recommendations based on Eurocode I were used to predict the vertical loading on the disc and cylinder embedded in grain. This technique did an adequate job of predicting the maximum loading on both obstructions within the bin; however, it did not take into account the effect of unloading on the obstruction forces

Vertical Wall Loads in a Model Grain Bin with Non-Axial Internal Inserts

A study was conducted to estimate the degree of load asymmetry in a bin with non-axial internal inserts. Internal inserts in the form of an annulus segment were attached to the wall, and their influence on vertical wall loads during centric filling and discharge in a model bin were measured. Wall and floor loads were measured in a corrugated-wall model grain bin with a diameter of 2.44 m and a height of 7.3 m filled with soft red winter wheat to a depth of 6.7 m (height-to-diameter ratio of 2.75). Tests were conducted with inserts that extended circumferentially 30°, 60°, or 90° around the bin, having a width of 7.6, 15, or 23 cm and attached to the bin wall at height-to-diameter (H/D) ratios of 0.31, 0.62, or 0.95. These inserts represented between 1% and 8.6% of the bin floor area. The results showed that with centric filling, considerable asymmetry of static wall loads occurred. The asymmetric loading was caused by the horizontal component of the velocity of the grain stream filling the bin, produced by the drag conveyor. This loading created wall moments in the bin of approximately 3 kN-m. The wall moments generated by imperfect centric filling varied depending on the angular position of the inserts. For a 23 cm wide, 90° insert, which was the worst observed situation, the wall moment was approximately 5 kN-m. The onset of symmetric discharge resulted in an increase in vertical wall load and a decrease in the wall moment. A change in flow pattern from mass flow to funnel flow, as well as the influence of the insert, was clearly shown by the change in wall moment with discharge time

Airflow Resistance of Seeds at Different Bulk Densities Using Ergun\u27s Equation

Airflow resistance of grains and oilseeds has been extensively studied. Traditionally the data has been presented using Shedd’s curves. However, this assumes that airflow resistance is independent of grain depth. Grain undergoes compaction during storage that changes the bulk density, porosity, and therefore the airflow resistance. Ergun’s equation is a function of particle size and porosity of the granular material. Airflow resistance by Ergun’s equation was used to predict the pressure drop across a column of corn, soft white winter wheat, soft red winter wheat, and soybeans at three moisture content levels and two bulk densities. The maximum root mean square error when predicting airflow resistance using Ergun’s equation was less than 23 Pa/m when the pressure drop was less than 500 Pa/m. If all data was included up to a pressure drop of 1800 Pa/m, the average root mean square error for calculating airflow resistance was 76 Pa/m. The effect of grain orientation that would be typical in storage bins was negligible, less than a 10% increase in airflow resistance over a range of kernel orientations that varied between -10°, +10°, and 20° from the angle of repose. However, the fill method and resulting bulk density increased the airflow resistance by an order of magnitude. Ergun’s equation, with an appropriate model of porosity variation within a storage bin, could be utilized for the design and analysis of grain aeration systems

Friction of Wheat: Grain-on-Grain and on Corrugated Steel

Coefficients of friction of wheat for grain–on–grain and on galvanized corrugated steel sheet were investigated using a modified direct shear apparatus. Tests were conducted under a normal pressure of 20.7 kPa using soft red winter wheat at a moisture content of 11.2% (w.b.) and an uncompressed bulk density of 740 kg/m3. Three consolidation procedures and three methods of deposition of grain in the test chamber were used. Test results of grain–on–grain friction showed that consolidation procedure markedly influenced the force–displacement relationship, while its influence on the coefficients of friction were small. Shearing to peak strength as a consolidation method erased all effects of loading history and resulted in the highest values of the coefficient of friction. Grain–on–grain coefficients of friction were in a range from 0.47 ± 0.007 to 0.56 ± 0.004 depending on the method of grain deposition. Friction on two dimensionally different samples of corrugated steel sheet was examined using three methods of grain deposition. Corrugation depths were 13 mm on both samples, while their periods were 67.5 mm (short) and 104 mm (long). Coefficients of friction on the short–period corrugated samples were in a range from 0.42 ± 0.0 to 0.46 ± 0.004 and were significantly higher (α = 5%) than those on the long–period corrugated sample, which ranged from 0.36 ± 0.003 to 0.39 ± 0.003. The method of grain deposition significantly (α = 5%) influenced the coefficients of friction of wheat on both types of corrugated steel sheet

Asymmetry of Model Bin Wall Loads and Lateral Pressure Induced from Two- and Three-Dimensional Obstructions Attached to the Wall

An obstruction attached to the wall of a bin produced by cohesive, moldy grain has been reported as a source of failure in steel bins. A study was conducted to estimate the effect of two-dimensional (plane) and three-dimensional (block) obstructions attached to the corrugated wall in a flat-floor model bin where the lateral wall pressure and vertical wall loads were measured. The model bin was 1.83 m in diameter, 5.75 m high, and filled with soft red winter wheat to a depth of 5.0 m (height-to-diameter ratio h/d of 2.75). The plane obstruction had the form of an annulus segment spanning 60° of the bin wall and a width of 0.154 m (surface area of 7.2% of the bin floor area). A three-dimensional obstruction was shaped as a block with two bases identical to the plane obstruction and a height of 0.5 m. The plane obstruction and the upper base of the block obstruction were attached to the wall at h/d ratios of 1.26, 0.81, and 0.38. Even in conditions of near symmetry during centric loading, wall overturning moments of approximately 1 kNm were observed. The highest wall moment measured was 2.7 kNm at the end of filling with the block attached at h/d of 0.38; the moment with a plane obstruction in the same position was 2.1 kNm. Without an obstruction attached to the wall, the maximum lateral pressure increased 2.5 times relative to the static pressuer compared to an increase of 4 times with an obstruction. The data collected indicated that there are considerable additional loads imposed on a bin due to obstructions that may form during storage that are not considered in the design codes and could approach levels observed during eccentric discharge

Mechanical Properties of Corn and Soybean Meal

Ground corn and soybean meal are common ingredients in feed mixes. The knowledge of their mechanical properties is important to the feed manufacturer and consumer. Changes in these properties can lead to abnormally high or low levels of active ingredients in finished feed, thus decreasing its quality. Mechanical properties of wheat, corn meal, and soybean meal were investigated using a modified direct shear apparatus. The moisture content (wet basis), uncompacted bulk density, and particle density were: 10.4%, 733 kg/m3, and 1410 kg/m3 for soft red winter wheat; 11.4%, 583 kg/m3, and 1350 kg/m3 for soybean meal; and 11.7%, 595 kg/m3, and 1410 kg/m3 for corn meal, respectively. A relatively long sliding path of 60 mm was utilized in shear testing to account for the high compressibility of the materials and minimize boundary effects. The compressibility of the materials was determined at a maximum vertical pressure of 34.4 kPa, which caused a density increase of 21% for corn meal while the density of wheat and soybean meal increased by approximately 5%. Frictional properties were tested for seven levels of vertical consolidation pressures ranging from 4.1 to 20.7 kPa. The high compressibility of corn meal resulted in severe stick–slip behavior of the frictional force–displacement relationships. The angles of internal friction of wheat, soybean meal, and corn meal were found to be 26.3° ±0.3°, 33.9° ±0.9°, and 30.7° ±1.4°, respectively. Cohesion of soybean meal and corn meal was approximately 0.7 kPa without a clear relation to consolidation stress and approximately 0.3 kPa for wheat. With cohesion values lower than 4 kPa, all three materials should be treated as free–flowing in terms of Eurocode 1. Corn and soybean meals are known to cause flow problems in practice that were not confirmed during testing. In practical storage conditions, materials undergo a longer consolidation period. Our tests have shown that with processes that have a short duration and low consolidation pressures, these materials should be treated as free–flowing

Airflow Resistance of Wheat Bedding as Influenced by the Filling Method

A study was conducted to estimate the degree of variability of the airflow resistance in wheat caused by the filling method, compaction of the sample, and airflow direction. Two types of grain chambers were used: a cylindrical column 0.95 m high and 0.196 m in diameter, and a cubical box of 0.35 m side. All factors examined were found to influence considerably the airflow resistance. Gravitational axial filling of the grain column from three heights (0.0, 0.95 and 1.8 m) resulted in the pressure drops of 1.0, 1.3, and 1.5 kPa at the airflow velocity of 0.3 m/s. Consolidation of axially filled samples by vibration resulted in a maximum 2.2 times increase in airflow resistance. The tests with cubical sample showed that in axially filled samples the pressure drop in vertical direction was maximum 1.5 times higher than in horizontal directions. In the case of asymmetrically filled samples, the pressure drop at the airflow velocity of 0.3 m/s in vertical direction Z was found to be 1.3 of that in horizontal direction X and 1.95 times higher than with horizontal direction Y, perpendicular to X. Variations in airflow resistance in values comparable to that found in the present project may be expected in practice