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 due to cohesive, moldy grain has been reported as a source of failure in steel bins. These obstructions were modeled using eccentric structural members fastened to the wall. A study was conducted to estimate the effect of a two- (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 load were measured. The bin was 1.83 m in diameter and 5.75 m high filled with soft red winter wheat to a depth of 5.0 m (height-to-diameter ratio h/d of 2.75). Geometrical imperfections in the bin and imperfect centric loading and unloading of the bin were observed to produce significant unsymmetrical states of stress even under nearly symmetrical conditions of operation. The plane obstruction had the form of an annulus segment of 60° in circumferential extension 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 as the plane obstruction and a height of 0.5 m. The plane obstruction and upper base of block obstruction were attached to the wall at h/d ratios of 1.26, 0.81 and 0.38. Lateral pressure was determined using two pressure cells attached above and below the obstruction. In the following test the pressure determination was taken with the obstruction removed from the bin. Simultaneously vertical wall and floor loads were measured that allowed for evaluation of wall load asymmetry. Even in conditions of near symmetry during centric loading, wall overturning moments of approximately 1 kNm were observed. Attachment of an obstruction resulted in an increased moment. The highest wall moment of 2.7 kNm was found at the end of filling the bin with the block attached at h/d of 0.38, the moment with a plane obstruction in the same condition was measured as 2.1 kNm. The maximum moment measured in this bin for eccentric unloading with no obstruction was 3.5 kNm. For higher locations of the obstruction on the wall, wall moments were found approximately 50% of the value at h/d of 0.38. Lateral pressure distribution along the bin height during filling was found in good agreement with Janssen's equation. At the onset of discharge a sudden increase in lateral pressure was observed. Without an obstruction attached to the wall a maximum pressure increase of 2.5 times the static pressure was observed. Dynamic pressure increases above the obstruction were a maximum of four times the static pressure. Conversely dynamic pressure increases below the obstruction were lower than without the obstruction attached. The data collected indicated that there are considerable additional loads placed on a bin due to obstructions that may form during storage that are not considered in the design codes.