Steel structure concrete

Structures or pits for water lines are mostly of steel-reinforced concrete. At the wall entrance, contact can easily arise between the pipeline and the reinforcement. In the immediate vicinity of the pit, insufficient lowering of the potential occurs despite the cathodic protection of the pipeline. Figure 12-7 shows that voltage cones caused by equalizing currents are present up to a few meters from the shaft. With protection current densities of 5 mA mr for the concrete surfaces, even for a small pit of 150 m surface area, 0.75 A is necessary. A larger distribution pit of 500 m requires 2.5 A. Such large protection currents can only be obtained with additional impressed current anodes which are installed in the immediate vicinity of the pipe entry into the concrete. The local cathodic protection is a necessary completion of the conventional protection of the pipeline, which would otherwise be lacking in the pit. 

Very often steel sheet pilings exist in conjunction with steel-reinforced concrete structures in harbors or locks. If cathodic protection is not necessary for the reinforced concrete structure, there is no hindrance to the ingress of the protection current due to the connection with the steel surfaces to be protected. The concrete surface has to be partly considered at the design stage. An example is the base of the ferry harbor at Puttgarden, which consists of reinforced concrete and is electrically connected to the uncoated steel sheet piling. 

Harbor structures are very accessible and can be investigated without the effects of wave motion. Grounding of steel pilings presents no problems and the work can be carried out from the quay (see the left-hand side of Fig. 16-13). With steel-reinforced concrete structures, measurements have to be made from a boat if no reliable contact has been provided in their eonstruction (see the right-hand side of Fig. 16-13). 

Cathodic Protection of Reinforcing Steel in Concrete Structures... 

Cathodic protection of reinforcing steel with impressed current is a relatively new protection method. It was used experimentally at the end of the 1950s [21,22] for renovating steel-reinforced concrete structures damaged by corrosion, but not pursued further because of a lack of suitable anode materials so that driving voltages of 15 to 200 V had to be applied. Also, from previous experience [23-26], loss of adhesion between the steel and concrete due to cathodic alkalinity [see Eqs. (2-17) and (2-19)] was feared, which discouraged further technical development. 

Cathodic Protection of Reinforcing Steel in Concrete Structures, Proposed NACE-Standard, Committee T-3K-2 NACE, Houston 1985. 

Cathodic protection can be used as a renovation measure for steel-reinforced concrete structures (see Chapter 19). Although material costs of from 100 DM m" (particularly with preparation, erection, and spray coating costs) up to 300 DM m are quite high, they do not compare with the costs of demolition or partial replacement. ... 

MKI The Mark I containment consists of two separate structures (volumes) connected by a series of l.irae pipes One volume, the dry well, houses the reactor vessel and primary system components. The other i oUmic is a torus, called the wetwell, containing a large amount of water used for pressure suppression and as, i heai sink. The Brunswick units use a reinforced concrete structure with a steel liner. All other M,uk 1 cnni.un ments are free-standing steel structures, The Mark I containments are inerted during plant oper.mon i. prevent hydrogen combustion. 

In all blast-resistant structures (steel, concrete, or masonry) special attention should be given to the integrity of connections between structural elements up to the point of maximum response. For example, it is important to prevent premature brittle failure of welded connections to avoid stress concentrations or notches at joints in steel structures and to provide ductile reinforcement detailing in concrete/masonry structure connections. For all materials, it is recommended that connections be designed to be stronger than the connected structural members such that the more ductile member will govern the design over the more brittle connection. 

Cast-in-place concrete construction (Figures 4.3 and 4.4) is used to resist relatively high blast overpressures where precast concrete is not economical or practical. Horizontal loads are resisted by shear walls. The structure depends on a structural steel or concrete frame to support vertical loads. Thickness of the concrete... 

Limit state design methods are used in blast resistant design. These methods provide a comprehensive, reliable and realistic means of predicting failure mechanisms and structural capacities. Limit state design methods for structural steel, cold formed steel, reinforced concrete and reinforced masonry are available. However, as of now, no similar design specification is available for aluminum structures. 

This chapter presents an overview of various details applicable to blast resistant structures. Many details for conventional steel and concrete structures, and specific details for seismic design, are applicable to these structures and are not included. Details should meet the requirements of design capacity, energy absorption, and ductility. 

The use of pesticides in stored products in tropical countries cannot be separated from the broader field of economics and engineering. In order to use more pesticides efficiently, storage structures must be built. They, in turn, must be suited to the needs of the country and located so that they may be used economically. The jute bag is a poor, but costly storage unit. Its cost should be compared with steel or concrete over a period of 30 or 40 years. With improved facilities, a steady increase in the use of pesticides will be seen. Management must be improved also to install sanitary practices along with efficient and sensible use of pesticides. Because of the distances involved, freight rates are important and because of the small dosages required, methyl bromide is favored thereby. 

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