Silos wall load

Laboratory Exercise Evaluation of Wall Loads in Silos... 

Roberts, A. W. 1988b. Some aspects of grain silo wall pressure research-influence of moisture content on loads generated and control of pressures in tall multi-outlet silos. Proceedings of the 13th International Powder and Bulk Solids Conference, Chicago. 

Rotter, J.M. Hull, T.S. (1989) Wall loads in squat steel silos during earthquakes. Eng. Struct., 11(3), 139-147. 

Support beams, inverted cones, blend tubes, and other types of internals can impose large concentrated loads and/or non-symmetric pressures on a silo wall leading to unacceptable... 

Another unusual loading condition can occur when moisture migrates between stagnant particles, or masses of stagnant particles, which expand when moisture is added to them. If this occurs while material is not being withdrawn, upward expansion is greatly restrained. Therefore most of the expansion must occur in the horizontal plane, which will result in significantly increased lateral pressures on, and hoop stresses in, the silo walls. 

G. E. Blight, Temperature-induced loadings on silo walls. Structural Engineering Review 4 No. 1,1992, pp. 61-71. 

In the experiments 5 different vertical positions of the internal cone were tested, varying between 268 mm and 868 mm in distance between the outlets of the silo itself and the internal cone. In addition to monitoring the flow patteni, the vertical load on the insert as well the stresses on the silo walls were also measured. For the measurement of normal- and shear stresses on the walls, 6 two-component stress cells were installed, see Figure 2. The measuring frequency is up to 2 per second [4]. 

Load cell systems. By mounting load cells either on the lower side wall section or structural leg supports of a silo, direct measurement of material weight can be taken. This method is accurate and the only choice where certified weight requirements exist. 

The dry storage is located on the first floor of the reactor building and consists of horizontal silos in a concrete wall. The spent FAs in dry storage were those of the first load that had corroded and had released fission products in the early stages of reactor operation. Their burnups were almost nil, but some of them had a dose rate of more than 1 R/h on the FA surface. These FAs were wrapped in plastic bags. 

In reading what follows it should be noted that metal silos are most sensitive to vertical compression in the vertical walls, that concrete silos are most sensitive to normal pressures against the walls, and that both of these structural materials are easily damaged by unsym-metrical pressures, as noted in Sections 3.4.5 and 3.5. Finally, the hopper, which has not been discussed yet, is usually chiefly loaded by the vertical stress in the solid at the transition. These different sensitivities demand that careful attention is paid to different parts of the pressure theory, since it is not normal wall pressures alone that cause structural failures. 

Bursting of the vertical wall Bursting failures are very uncommon and are almost all found in bolted silos where a joint detail has failed. A careful analysis of the loads and strengths in different modes shows that this failure mode is only critical near the surface, or in squat silos. 

Shear buckling of the vertical wall Where a squat silo (low aspect ratio) is either eccentrically filled (unsymmetrical top pile producing different heights of solid-wall contact) or is subjected to seismic excitation, the wall can buckle in shear near the foundation. These buckles have a characteristic diagonal stripe shape, but these load cases are relatively rare. 

Finally, where silos may be subjected to seismic loads, much care is needed. In elevated silos, a huge mass is supported on a relatively soft spring, leading to a low natural frequency which is easily excited by seismic waves. In on-ground silos, vertical compressions and high shear forces develop in the walls due to the horizontal excitation (Rotter Hull 1989), and care must be taken to ensure that the structure is strong enough, but also to ensure adequate connection in the base details. Some information may be found in EN 1998-4 (2006). 

Changing material properties or polishing of the inside surface of the silo may cause mass flow to develop in a silo which was structurally designed for funnel flow. (The opposite can also occur - funnel flow in a silo designed structurally for mass flow - but this generally is not as serious a problem.) Mass flow will result in a dramatically different wall pressure loading than with funnel flow, particularly at the top of the hopper section. 

Four outdoor bolted silos were used to store barley and com. As with the previous example, failure occurred by splitting of a radial seam near the top of the hopper, which was the result of imexpected mass flow loads. In this case the cone walls were apparently polished by the barley, and the wall friction decreased further when the outside air temperature dropped below freezing. 

The loads on silo bin walls consist both of static and dynamic actions caused by pressure of stored granular material and operating simultaneously thermal actions due to e.g. seasonal or daily fluctuations of ambient temperature. Such thermal actions should be taken into consideration as required by Eurocode 1 part 4 [1]. 

Theoretical analysis of tangential thermal stresses in the silo bin requires considering both static and thermal loads including the grain-wall structure interaction phenomenon when the bin is subjected to rapidly decreasing temperature [4], [8]. 

The experimental studies on the large scale silo model under static and thermal loads modelling daily ambient temperature changes were conducted at Bialystok Technical University [9]. The experimental stand consisted of a ferrocement model of cylindrical silo bin with additional surcharge installation of bulk material, wall temperature distribution system and also strain gauges system for measurements of physical quantities. 

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