Sidney A. Thompson

BIN LOADS INDUCED BY ECCENTRIC FILLING AND DISCHARGE OF GRAIN

Wall loads were measured in a corrugated–wall model grain bin 2.44 m in diameter and 7.3 m high filled with wheat to a H/D ratio equal to 2.0. The model bin was filled either centrally or eccentrically through a chute located along a radial line, coinciding with one of the major axis of the bin, at eccentricity ratios of 0, 0.5, or 0.75. The eccentricity ratio (ER) is defined as the ratio of the distance from the center of the bin to either the filling location or the discharge gate divided by the radius of the bin. The model bin was unloaded either centrally or eccentrically through discharge gates located at ERs of 0, µ 0.5, or µ 0.7. For both an ER of 0.5 and 0.7, two different eccentric discharge gates were used, located on opposite (plus or minus) sides of the bin on a major axis that was parallel to the filling axis. For experiments involving centric filling followed by eccentric unloading, a maximum wall moment of 11.2 kN–m was measured. For experiments involving eccentric filling followed by eccentric unloading, the mutual location of the filling and discharge gates either magnified or reduced the variation in stress within the bin and the resulting moment carried by the walls. For experiments in which the location of both the filling and discharge gates were on the same side of bin, a maximum wall moment of 17.5 kN–m was measured. For tests in which the filling chute was located on the opposite side of the bin from the discharge gate, a maximum wall moment of 3.2 kN–m was measured.

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.

EFFECT OF MOISTURE CONTENT AND BROKEN KERNELS ON THE BULK DENSITY AND PACKING OF CORN

Shelled yellow dent corn samples were conditioned to three moisture content levels (12%, 15%, and 18% w.b.) and mixed with a prescribed amount of broken corn particles of known size (geometric mean diameter of 1.0, 1.4, 2.0, 2.8, and 4.0 mm) and concentration (2.5%, 5.0%, and 7.5% by weight) levels. The initial bulk density and grain compaction under simulated overburden pressure tests were determined for each sample. Uniaxial compression tests were performed for seven vertical pressure levels (3.4, 6.9, 14, 28, 55, 110, and 165 kPa) with a minimum of three replications each. Tests were performed at two locations with identical apparatus, which was fully described by Thompson and Ross (1983). These devices used compressed air injected beneath a rubber diaphragm to apply vertical pressure uniaxially to a volume of granular material. Deflections of the grain mass were measured with a dial gauge and were used to calculate changes in bulk density and grain packing. Statistical models were tested for the initial bulk density and packing factor as a function of moisture content, broken corn particle size, and broken corn concentration level and their interactions. For clean corn, the initial bulk density was inversely affected by grain moisture while packing increased slightly with grain moisture. For corn mixed with fines, the initial bulk density decreased with grain moisture and the interaction of broken corn particle size and concentration but increased with the interaction of grain moisture and concentration of fines. Packing of corn mixed with fines increased slightly with grain moisture and broken corn concentration. For a given pressure, the predicted bulk density from the developed model was within 4% of the observed value, which was within the variation among test replications and may in fact represent observed differences in bulk density caused by bin loading methods that have been reported by other engineers. The results can improve predictions by WPACKING, the ASAE standard for estimating capacities of cylindrical grain storage structures.

Asymmetry of Bin Loads Induced by Eccentric Discharge

A series of tests involving eccentric discharge from a model bin were conducted using bin wall surfaces of smooth galvanized steel, corrugated galvanized steel, and abrasive paper simulating a concrete bin wall. Bin load asymmetry resulting from eccentric discharge was found to decrease with increasing value of friction coefficient of the bin wall.

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.

LOADS CAUSED BY BOTTOM UNLOADINGWALL FLUMES IN A MODEL GRAIN BIN

Wall loads were measured in a model bin 2.44 m in diameter and 7.3 m tall equipped with a bottom unloading wall flume. The results were then compared to the wall loads measured during unloading of this same bin without the flume. During most of unloading the wall loads measured when using the flume were smaller than those during filling. However, at the onset of discharge a load spike was observed prior to the formation of the funnel-flow discharge pattern. Wall moments in the direction of the flume were observed to occur which were three times as large as those measured during centric unloading.

FORCES ON TEMPERATURE CABLES IN A MODEL BIN UNDER RESTRAINED CONDITIONS

ABSTRACT mperature cables restrained from lateral movement, were measured as a function of grain height, cable location and surface coating. For the restrained conditions, the cable forces were one to nine times those previously measured for unrestrained cables. The large load increase on the restrained cables is believed to be caused by the flow profile which existed at each of the three different cable locations. The flow profile at the center cable is predominantly vertical and the forces in the restrained condition resembled those in the unrestrained condition. For the two outer cable locations, both vertical and lateral force components exist because of the nature of the discharging grain at these two different locations. For the restrained condition, the largest forces occurred on the cable located at the middle position. For the unrestrained condition, the largest forces occurred on the cable located at the wall position. Surface coatings on the cable had an effect on the magnitude of the forces. Forces on vinyl coated cables were significantly larger than either the nylon or HDLE polyethylene coated cables in the restrained condition.

Calibration of a Model for Packing Whole Grains

The computer program WPACKING was validated using bin data for three different bin conditions: 1) a smooth-walled bin filled with wheat, 2) a corrugated-walled bin filled with wheat, and 3) a corrugated-walled bin filled with corn. WPACKING is a computer program which utilizes the differential form of Janssen’s equation to predict the pressures and amount of material stored in a bin. The differential form of Janssen’s equation allows the material properties in the equation to vary as a function of different properties. The material properties suggested for use in the WPACKING program were based upon previous experimental work by various researchers. From using the WPACKING program, it was apparent that a change in grain height has a greater effect in increasing the amount of packing than does a change in bin diameter or moisture content of the stored material.

Technical Note: Packing Factors of Feed Products in Storage Structures

Experiments were conducted to measure the changes in bulk density of cracked corn, corn meal, soybean meal, cotton seed meal, and distillers dried grain (without solubles) when subjected to simulated overburden pressures. All materials were tested at two moisture content levels (approximately 8% and 12% w.b.) and seven pressures between 0 and 69 kPa (0 and 10 psi). A mathematical model was fitted to the data to predict the bulk density of each feed ingredient as a function of pressure and moisture content. These relationships were inserted into a previously developed computer model to predict ingredient packing within conventional storage structures based on Janssens equation as a function of feed product type, moisture content of the material, friction characteristics of the bin wall material, material height, and bin diameter. Cracked corn experienced the smallest amount of packing (approximately 4.3% in a bin with a diameter of 1.8 m and a height of 1.8 m), while distillers dried grain (without solubles) had approximately 8.1% packing in the same sized bin. With a bin diameter of 5.5 m and a height of 5.5 m, distillers dried grain (without solubles) and cracked corn had a packing factor of 13.3% and 6.8%, respectively. As moisture content increased the amount of packing increased for all materials. The data presented can be used for inventory control and management.

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.