Reinforced concrete shells

Rebora, B. et al Dynamic Rupture Analysis of Reinforced Concrete Shells. Paper S 2/3, ELCALAP Berlin (1975)... 

Membrane or cable net skin replaces the reinforced concrete shell of conven towers. 

When options for reinforcing an existing structure are not feasible, an independent concrete shell (or cocoon) can be built around the structure, Factors which make shells an attractive option include ... 

Another important item is to consider how the finite element output data would be used to confirm compliance with acceptance criteria. For example, using stress output data from plate or shell elements to evaluate a reinforced concrete slab is not... 

For most utility and large industrial chimney applications, reinforced concrete chimney shells have been specified because of their relatively low costs of initial construction and subsequent maintenance. In chimneys where a fairly large outer shell diameter s required (10 to 12 ft.), the cost of a cast-in-place concrete structure is typically less than field welded steel. Since this chapter must necessarily limit itself to that approach most popularly specified, it will describe in further detail only the cast-in-place reinforced concrete outer shell without further consideration of steel or radial brick. (See Figures 48-4 and 48-5). 

In summary, there has been a great deal of research and analysis pertaining to the concrete chimney shell. All known effects have been studied thoroughly and can be incorporated in design. Both the owner and consulting engineer can feel confident that, when properly constructed, the exterior shell of a reinforced concrete chimney will provide a long and trouble-free service life. 

Carbon fiber reinforced concrete can be utilized to achieve three times higher tensile forces compared to steel reinforced concrete. The tensile stress at break is even six times higher. Moreover the fibers are as far as possible insensitive against corrosion. This leads to a higher durability. Mader et al. for example proclaims that a shell like structure out of calcium-silicate-hydrate-phases and calciumhydroxid-phases are formed around the carbon fiber. Hence, the interface and the fiber itself are damaged. This leads to a brittleness and a prematurely failure. 

Figure 5-4. Conceptual scheme of a composite containment for a PWR (internal steel shell and external structure in reinforced concrete from J. EibI, reproduced courtesy of Forschungszentrum, Karlsruhe, Germany).

Of the discarded marine reactors, six of the 16 contained their spent nuclear fuel (SNF). In addition, approximately 60% of the SNF from one of the three icebreaker reactors was disposed of in a reinforced concrete and stainless steel (SS) shell container. The vast majority of the low and intermediate level solid radioactive waste was disposed of in containers of unknown composition. The Kara Sea disposal sites for the 16 marine reactors and low and intermediate level solid radioactive waste varied in depth from 12 to 380 m. In particular, the icebreaker reactors and part of their SNF were reportedly disposed of in Tsivolka Fjord at an estimated depth of 50 m. 

As a consequence of the accident, only 94 of the 219 TFCs from the N2 RPV could be disposed of in a normal manner. The remaining 125 TFCs and the core barrel from the N2 RPV, hereafter known as Configuration A, were placed within a reinforced concrete and SS shell container, hereafter known as Container B. Figure 9 shows a schematic cross-section of Configuration A. Container B consisted of the following constructions ... 

The sound field generated within the shell does not affect the tube bundle unless the acoustic resonance frequency approaches the tube natural frequency. However, very loud, low frequency noise can be emitted. Also, fluctuating forces are developed that can potentially destroy the shell, anchor bolts, and reinforced concrete foundations, and can cause severe vibration of connecting piping. Yet another effect sometimes noticed is an increase in pressure losses with the onset of resonance. 

Fig. 20.11 Reinforced concrete panel test facilities (a) shell element tester at University of Toronto, (b) universal element tested at University of Houston...

Generic Safety Issue (GSI) B-05 in NUREG-0933 (Reference 1), identifies two concerns relating to containment design. First, that sufficient information is not available to predict the behavior of two-way reinforced concrete slabs and second, that the structural design of a steel containment vessel subjected to unsymmetrical dynamic loadings may be governed by the instability of the shell. 

The upper hemisphere of the steel shell is surrounded by a shielding made of reinforced concrete with a wall thickness of about 2 m. This shielding protects the nuclear part of the plant against any external impact (e. g. gas explosion, military aircraft crash) it also significantly reduces the likelihood that radionuclides will escape to the environment. The interspace between the steel shell and the secondary containment is held at sub-atmospheric pressure, so that any radionuclides penetrating the steel shell via leaks in the event of a loss-of-coolant accident would be transported by the annulus air extraction system to the standby filters and retained here, thus preventing release to the environment. 

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