Reinforcement works include the following processes:
• centralized preparation of reinforcement elements;
• transportation of fittings to the construction site, sorting and storage;
• pre-assembly of reinforcing elements, manufacturing of reinforcement products;
• installation of cores, grids, flat, spatial and bearing reinforcement cages in the formwork;
• connection of separate installation units into a single armored structure;
• detachment of armored structures, ensuring the provision of a proper protective layer during concreting.
All the processes of reinforcement of reinforced concrete structures can be combined into two groups: the preliminary manufacture of reinforcing elements and their installation in the design position.
3. Manufacturing of reinforcement products
Reinforcement products are manufactured centrally in reinforcement-welding plants, in reinforcement workshops and workshops.
Wire with a diameter of up to 10 mm and steel of a periodic profile with a diameter of up to 9 mm enter the reinforcement workshop in coils, and steel of large diameters — rods from 4 to 12 m long, combined into packages up to 10 tons. Ready meshes for billet frames are delivered flat or in rolls . Store the steel on the racks separately by brand, diameter and length of the rods. Storage is carried out indoors or under a canopy, it is forbidden to lay the fittings on the earthen floor.
The process of manufacturing non-stressed reinforcement consists of separate technological operations, which are combined into the following technological groups:
harvesting operations include: cleaning and straightening rods; joining rods into continuous lash by butt welding; marking and cutting rods of the required length; welding 
operations performed by resistance spot welding for flat grids and skeletons on single- and multi-electrode machines, as well as butt and arc welding;
assembly operations , including the installation and welding of embedded parts, separate curvilinear and curved rods, cutting sheet and profile steel, pre-assembly of spatial frames from flat frames and grids.
Procurement operations are carried out in two streams - for wire rod and bar reinforcement. Steel coming in coils (wire rod) from coil holders is sent to automatic machines, which simultaneously clean the surface of the rod from rust, straighten the curvature of the wire and cut it. The ends of the ending and the new coil are joined into a continuous whip by a butt welding machine. In the course of movement of the rod, machines for precise cutting and bending are installed.
The rods coming to the process chain are ruled, cleaned of rust, butt-welded into a continuous whip to avoid waste, then they are cut into pieces with specified sizes and, if necessary, transferred to a bending machine.
4 Connection of reinforcing elements. Welding methods
Installation of reinforcement and reinforcement products is carried out by machines and mechanisms used at the construction site. In some cases and in places that are inconvenient for the mechanisms to be used, manual installation of the armature and its binding are performed.
The main methods of connecting reinforcing bars between them are overlapping or welding. An overlap joint without welding is used to reinforce structures with welded meshes or flat frames with a one-sided arrangement of working reinforcement bars and with a diameter of reinforcement not exceeding 32 mm. In this method of fitting the reinforcement, the value of the bypass (overlap) depends on the nature of the element, the location of the joint in the section of the element, the class of concrete strength and the class of reinforcing steel.
When joining to the welding of grids of round smooth rods, at least two transverse rods should be placed within the joint. When joining grids of rods of a periodic profile, it is not necessary to weld transverse rods within the joint, but the length of the overlap in this case should be increased by at least five diameters of the welded reinforcement. Rod joints in the non-working direction (transverse mounting rods) are performed with a bypass of 50 mm with a diameter of distribution rods up to 4 mm and 100 mm - with a diameter of more than 4 mm. When the diameter of the working reinforcement is 26 mm and more welded meshes in the non-working direction, it is recommended to stack close to each other with the joint overlapping with special butt grids with bypass in each direction at least 15 diameters of distribution armature, but not less than 100 mm.
When welding fittings between themselves, the metal has a slight resistance to the passage of electric current. In accordance with the Joule-Lenz law, to reduce welding time and increase labor productivity, high currents of up to 50,000 A and low voltage are used — no more than 30 ... 60 V. During contact welding at the site of contact, resistance to movement of electric current is large times the resistance on the rest of the current path, heat is strongly released here, the metal is heated to a plastic state, the intersection of the rods is compressed and their welding takes place.
In the chain, the junction of the rods has the highest resistance, in this place the most intense heat is released, which heats the ends of the rods to a plastic and partially liquid state. At the same time, the metal at the welding site melts almost instantly, the transmission time, the current is measured in fractions of a second. The rods with force pressed against each other, with the result that they are welded. For welding, special transformers are used, which reduce the voltage from nominal 220 ... 380 V to the required voltage and at the same time increase the amperage.
Electrical energy can be converted to heat in two ways:
1) passing the current through the welded parts; contact welding is based on this principle with the use of pressure, at which heating is produced by the heat released during the passage of electric current through the connected parts in contact;
2) using an electric arc or fusion welding; heating of the connected elements is carried out by an electric arc.
Contact welding. Contact welding has the following main types:
• resistance spot welding, used to join intersecting rods in grids and frames;
• butt resistance welding, which is suitable for connecting the rods between themselves, when an increase in their length is required, and also 'for splicing the trimmings and rods together.
Spot welding. The essence of this welding is that two rods (or more) in the place of their intersection clamp between the electrodes of the welding machine. When passing a current under the influence of 
In my heat, the metal of the rods in the welded place is heated red-hot, softens, and under the action of the squeezing force the rods are firmly connected to each other.
In automatic welding, the supply of parts, their fixing, the process of quarks and the issuance of finished products occurs without human intervention. In semi-automatic welding, parts are fed manually, and the finished product moves automatically after welding.
The rods coated with corrosion and scale are pre-cleaned at the point of contact, or two pulsed welding is used - at the first impulse, the scale is broken, at the second - the rods are welded.
The advantages of resistance spot welding are high performance, low energy consumption when using high currents: sludge for a short period of time, the possibility of mechanization and automation of the process, and the absence of metal consumption on the electrodes. The assembly, and then the welding of the abutting elements, is carried out with the use of conductors, which ensure the accuracy of the geometric dimensions of the mutual arrangement of the abutting rods.
Contact butt welding is performed by continuous and intermittent flashing.
Continuous flashing welding is characterized by the fact that two welded rods connected to an electrical circuit begin to slowly approach each other before contact and simultaneous closure of the current circuit. The fusion of the metal, which began when the chain was turned on, increases with the approach of the rods and ends with a strong compression of the melted ends. When the compression (draft) reaches the required value, the current is switched off, and the welded rods are removed from the terminals of the machine. The advantage of welding is that the weld can be located anywhere on the reinforcement cage or supporting structure.
Intermittent flashing welding . As a result of approaching: disconnection of the rods (at the same time the closures and openings of the electric circuit), the number of which varies from 3 to 20, the ends of the rods heat up and partially melt. The large diameter rods are thus heated to red or light red heat, then they are connected under pressure. Preheating increases the temperature of the rods being welded and thereby reduces the power required for welding. When butt welding, the rods clamped with the jaws of the welding machine are connected across the entire surface of their ends and, after the necessary preheating, are compressed.
The advantages of butt resistance welding are the high quality of the joints of the elements being joined, the minimum cost of electrodes and other auxiliary materials, the possibility of mechanization and automation of the welding process, and high labor productivity.
Electric arc welding. Arc welding, i.e. Electric arc welding, which burns in the atmosphere between the end of the metal electrode and the part being welded, is used most often.
Electric arc welding can be performed using both AC and DC. Welding on alternating current in comparison with other types of the most economical. Instead of complicated and cumbersome DC generators, light, mobile and cheaper AC transformers are used to obtain electric current of the required characteristics. The arc is an electrical discharge in a gas space that lasts a long time, emitting a large amount of light energy and having a temperature of up to 6000 ° C. The required heat output, measured in thousands of calories, is easily regulated by varying the strength of the current. The minimum voltage required to initiate the arc is at a constant current of 30 ... 35 V, and at alternating current - 40 ... 50 V.
Electrodes, which are used for welding, have a special coating that evaporates during welding, the resulting pairs are easily ionized and thus increase the stability of the arc. During melting, the metal of the electrode flows and, while cooling, forms a weld on the surface being welded, the strength of which also determines the strength of the welded joint as a whole. The length of the arc has its effect on the quality of the seam. The longer the arc, the greater the distance the molten metal travels from the electrode to the weld and, absorbing oxygen and nitrogen from the air, deteriorates its mechanical properties.
The advantages of arc welding - versatility, the ability to use at any point of a complex reinforcement cage and achieve the required strength of the weld. The disadvantages of arc welding are the additional consumption of metal on the electrodes, low labor productivity, higher qualification of welders is required. Rods with a diameter of 10 mm and more are usually welded, since with smaller diameters of the rods their burn-through is possible.
Of the existing methods of arc welding, the most common are the overlapped, with lining and bath (Fig. 8.3).
The essence of the bathing method of welding is that the electric arc is excited between the ends of the welded rods with the help of electrodes. The heat released melts the metal from the ends of the rods and from the electrode, resulting in a bath of molten metal. The gap between the rods is assumed to be 1.5 ... 2 diameters of the electrodes coated. For the formation of the bath using inventory copper forms and steel braces-lining. The method has a number of advantages in comparison with other types of arc welding - the consumption of metal at the joint decreases, the consumption of electrodes and electric power decreases, as well as the labor intensity and cost price. Bath welding is applicable to rods with a diameter of 20 to 80 mm.
In arc welding, one of the current conductors is attached to the parts to be welded, and the other to the electrode clamped in an electric holder. After switching on the current, the welder touches the welding spot with an electrode, thus closing the circuit, and immediately removes the electrode from the workpiece by 2 ..- A mm. The resulting arc melts the electrode core and partially welded parts, the metal of which is connected to the metal of the electrode. The temperature at the end of the metal electrode reaches 2100 ° C, at the welded elements - 2300 ° C, in the center of the arc column - about 5,000 ... 6,000 ° C.
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