Concrete silos

1 General Concrete is good in compression, but cannot resist tensile stresses at all. Unfortunately, silos are essentially structures in tension, holding in the stored solid. 

Vertical compression does not usually cause problems in concrete silos since the weight of concrete, the thickness and the good compressive strength all contribute to excellent strength. 

5 Durability considerations Reinforcement in concrete structures must be protected from corrosion, and the conventional manner of doing this is to have a suitable thickness of concrete cover over the steel. Where large cracks are able to develop in the concrete wall, the protective effect of this cover can be lost, and a significant loss of the area of reinforcement may occur. This leads to a dramatic loss of strength and has caused failures (Elghazouli Rotter 1996). 

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Farmers often store soybeans on the farm in aerated metal bins or at local grain elevators in concrete silos (100,000 to 700,000 bu/tank capacity). Higher prices are usu-... 

Inside storage systems, primarily concrete silos and metal bins, are used for storing soybeans at elevators and plant sites. Sometimes a shortage of available protected storage at peak harvest time exists. Unlike storing cottonseed in dry regions (e.g., west Texas) or corn in the Midwest, soybeans are rarely and for only very short periods stored on concrete pads without protection against the weather. 

Magnox cladding, which has been removed mechanically from spent fuel rods at the start of reprocessing operations, is contaminated with small pieces of fuel and will require treatment before disposal to the environment. At present, this waste is stored under water (to eliminate any fire risk) in large concrete silos and processes are now under development for the conditioning of this waste to make it suitable for disposal. The favored processing route comprises the following operations ... 

The lime-bnrning plant consists of 7 rotary kilns each 8 feet in diameter by 125 feet long from which the calcined lime is fed to 7 rotary coolers each 5 feet in diameter by 50 feet long. The I ated capacity of these Is 700 tons of calcined lime per day (24 hours) which is stored in four similar concrete silos of 250 tons capacity. Fuel for the time kilns is prepared in two Fuller indirect-fired rotary driers, 42 inches by 42 feet, and four Fuller-Lehigh mills. This plant has a rated capacity of 336 tons of dried and pulverized coal per day. 

Coke for carbide production is crushed in two crushing units of three sets of double crusher rolls each, and dried in four rotary driers 5 4 feet diameter by 40 feet long. This prepared coke is stored in four concrete silos of 160 tons capacity. 

The silo building between the cyanamide plant and the ammonia plant contains nine concrete silos of a capacity of 475 tons of cyanamide each. 

The PRISM reactor is positioned underground in a concrete silo—a fourth containment boundary (Figure 6.3). In the unlikely event of a containment breach, the sodium complies with the natural law of gravity and is contained in the silo. The silo is sized to retain all of the primary sodium while keeping the core, stored spent fuel, and heat exchanger inlets covered with sodium. 

Steel shield plates over alternate concrete silo... 

Due to the low bum-up of the fuel firom the pressurized heavy water reactors, storage in transport containers has been chosen. Design studies for reinforced concrete casks with stainless steel lining indicate cost of around US 45 per kg uranium. At present pools and concrete silos assure the interim at-reactor storage. If rq>rocessing is decided, then the plant would also be installed in the proximity of the disposal site to minmiize risks and costs of transportation. 

The design lifetime of the core and fuel as well as the reactor vessel and components is 30 years. The reactor building including the concrete silo can be used for more than 60 years. 

The STAR-H2 reactor is assumed to be sited in a silo underneath an earthen berm. Figure XXIV-13 shows a side view of the concrete reactor building, its earthen mound covering the building and the reactor vessel emplaced below grade in a concrete silo within the reactor building. 

Besides the temperature of the clinker there are also some other important aspects to consider in connection with the design of steel or reinforced concrete silos. It would be outside the scope of this book to go into these aspects of structural design. Further guidance is obtainable from, among others, the following publications ... 

A prestressed concrete silo of about 50 0001 capacity is illustrated in Fig. 2. Clinker is fed into it by two low-speed bucket elevators and is discharged through four bottom outlets. 

Metal and concrete silos carry their loads in very different ways, so the kinds of damage that can occur in each type are very different and the critical design considerations are different. For this reason, the later part of the chapter examines these two cases in separate sections. 

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. 

Eccentric discharge pressures of the pattern shown in Figure 3.23 also have a very damaging effect on concrete silos, where severe bending of the wall induces substantial vertical cracks and sometimes leads to spalling. 

The simplest stress analysis of a cylindrical silo structure under symmetrical loads was presented above in Section 3.3.5. Unfortunately, this is often the only analysis that is applied, sometimes with unfortunate consequences for the structure. Metal and concrete silos carry their loads differently because metals are strong in tension but thin metal sections tend to buckle under compression. By contrast, concrete is very weak in tension, but can resist compression well. These aspects lead to different key design considerations. 

Elghazouli, A.Y., Rotter, J.M. (February 1996) Long-term performance and assessment of circular reinforced concrete silos. Construction Build. Mater, 10(2), 117-122. 

Inspect silos routinely, both internally and externally. [29] This is particularly important with bolted and reinforced concrete silos, and silos which are exposed to a corrosive environment. For example, look for any signs of corrosion, exposed rebar, unusual cracking, or spalling of concrete. 

ACI Standard 313-91, Standard practice for design and construction of concrete silos and stacking tubes for storing granular nuiterials 1991. 

I.A.S.Z. Peschl, Construction of Concrete Silos, Silo Failures - An Analysis of the Reasons, Norwegian Society of Chartered Engineers, February 28-March 2,1977... 

G. E. Blight, Temperature surcharge pressures in reinforced concrete silos. Powder Handling and Processing 2 No. 4, November 1990, pp. 303 to 305. 

The paper presents some chosen results of studies concerning temperature effects on silos in operation and on a large scale silo model. It has been shown that cylindrical reinforced concrete silo bins are often subjected to cyclic thermal overpressure due to ambient temperature changes. Chosen experimental values of temperature distribution in a real silo have been presented in a form of diagrams. Also wall circumferential strains measured on the silo model have been compared with the theoretical strain values derived fi om an appropriate Finite Element Method (FEM) model. For the needs of practical calculations the nomograms of internal forces in the cylindrical silo bin sections have been also proposed. 

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