Reinforcement Manufacturing Operations
Reinforcement Manufacturing Operations
the complex of operations involved in the manufacture, placement in forms, or installation at the concreting site of reinforcement elements for reinforced-concrete structural members.
The growth in scope of construction using precast and monolithic reinforced concrete has required basic improvements in the technology of reinforcement manufacturing operations, as well as the invention of high-production machinery and equipment which allows these operations to be mechanized to the point where—together with a significant increase in the quality of reinforcement—the amount of labor required for the basic processes has been reduced by a factor of four to five. Moreover, there has been an improvement in the working conditions of those employed in reinforcement manufacturing operations. (In 1968 in the USSR there were about 100,000 workers in this field.) In 1970 the volume of production of precast reinforced concrete in the USSR reached approximately 85 million cubic meters, and the expenditure of reinforcement steel amounted to about 8 million tons.
The manufacture of reinforcement includes a number of operations.
Preparation of reinforcement rods. The preparation of reinforcement rods from reinforcement steel having a diameter of less than 10 mm and supplied in reels is carried out on precision automatic cutting units (see Figure 1); from large-diameter steel supplied in rods, by means of joining them together on contact-welding machines, followed by cutting on power-driven cutters. This process is also carried out on automated assembly lines, which in addition to units of the technical cycle include equipment for shifting, measurement of length, clamping, and ejecting the reinforcement rods after they have been cut. The bent parts of the finished rods are produced on bending machines before being assembled into frameworks.
Manufacture of reinforcement grids and frameworks. Reinforcement grids and frameworks are made out of pre-made rods by means of contact (spot) and electric-arc welding. Single-contact stationary machines are generally used for contact welding, but movable machines equipped with welding clamps, which have a productive capacity of 1,000 welds per hour, are also used. Broad reinforcement grids and flat frameworks are welded on multiple-spot, automated lines (see Figure 2). Electric-arc welding, which is basically done by hand, is being replaced by more highly perfected types of welding—for example, bath, semiautomatic welding with an open arc, and welding surrounded by a protective
gas. The feeding of the electrode wire into the welding zone has been mechanized. In order to ensure the proper quality of the welded reinforcement, various methods of control are in use, especially illumination by gamma rays, the magneto-graphic method, and ultrasonic “defectoscopy.”
Manufacture of reinforcement for prestressed reinforced-concrete structural members. Reinforcement for prestressed reinforced-concrete structural members is manufactured by units which perform the operations of unrolling the reinforcement, measuring out the necessary length, cutting, and assembling the packs, which consist of several wires, strands, or individual rods. Also used are reinforcement elements in the form of bundles of wires or strands and cables with bushing clamps press-fitted into their ends in order to hold and fasten the reinforcement while it is being stretched on forms, on stands, or in hardened concrete. This stretching (tensioning) of the reinforcement is carried out by hydraulic jacks (see Figure 3). Certain reinforced-concrete products (principally those used in housing construction) are manufactured by tensioning the reinforcement by means of the electrothermal method, in which the reinforcement is lengthened before being placed in the form by means of heating it to a temperature of 300°-450° C. The heating is accomplished by passing a high-voltage current through the reinforcement. After being placed in the form in its heated condition and with its ends fastened, the reinforcement is subjected to a predetermined amount of stress as a result of cooling.
Assembly and installation. The assembly and installation of reinforcement in monolithic concrete construction, setting footings under equipment, and so on is carried out with previously manufactured flat or three-dimensional frameworks and individual rods by using various types of welding. The operations of transporting and setting up the reinforcement into the formwork are carried out with the help of cranes, jigs, and other auxiliary equipment. Reinforcement manufacturing operations in the USSR are regulated by the Construction Norms and Rules, All-Union State Standards (GOST), and other normative documents.
REFERENCESNosenko, N. E. Izgotovlenie armaturnykh konstruktsii sbornykh zhelezobetonnykh izdelii. Moscow, 1958.
Nosenko, N. E. Mekhanizatsiia i avtomatizatsiia izgotovleniia armatury dlia zhelezobetona. Moscow, 1970.
Bogdin, N. M. Kontrol’ natiazheniia armatury pri proizvodstve zhelezobetonnykh predvaritel’no napriazhennykh konstruktsii. Moscow, 1959.
Brodskii, A. Ia. Svarka armatury zhelezobetonnykh konstruktsii. Moscow, 1961.
N. E. NOSENKO