Reinforcing steel is not officially called that way: if you study GOST 5781-82, you can find out that the correct name sounds like “hot rolled for reinforcing reinforced concrete”. However, the name was too long, so in a professional environment it was quickly reduced to a simple "fittings". This is both clearer, easier, and faster.
general information
It is customary to distinguish several classes of reinforcement. The division is based on the following features:
- periodic profile;
- mechanical parameters.
Reinforcing steel is of the following classes:
For several years now, the market has been quite demanding for the A500C class of reinforcing steel. If you study GOST 5781-82, there you will not be able to find descriptions of similar to it in its parameters. These products are manufactured with the following standards:
- STO AISU 7-93;
- technical conditions.
Such a standardization system, which groups hot rolled reinforcing steel of a periodic profile, is introduced by enterprises operating in the field of ferrous metallurgy. They are united in a single association, which has taken upon itself the development of rules for the production of goods.
A special case
The described A500C reinforcing steel is not the only exception in the world of hot-rolled products. Also, AI class deserves special attention, which in GOST is usually designated as A240. A key feature is a sleek profile. As raw materials for the production process, steel 3 SP (PS) is used. The diameter and deviations from it for any product with a smooth profile are regulated by GOST 2590-88. This normative document also specifies rolling accuracy for general cases.
Smooth reinforcing steel is produced in the following formats:
In skeins you can find sizes from 6 to 14 mm (pitch - 2 mm). The choice of reinforcement in bars is somewhat wider. The smallest possible diameter is 16 mm and the largest available is 40 mm. From 16 to 22 mm, the pitch is 2 mm, from 25 to 40 mm it increases to three.
How and why?
The grade of reinforcing steel A240 is necessary in construction and other areas where reinforced concrete structures are used, as it is used for their reinforcement. Some experts call this category of materials “loop”, since it is customary to use reinforcement to form loop-like elements reinforcing reinforced concrete products. This is most relevant when an element stands out from the main plane of the structure. Hot-rolled reinforcing steel A1 is suitable for creating elements that simplify the loading of finished blocks, transportation and unloading. In addition, directly at the construction site it is easier to connect different elements to each other.
The brand of AI fittings, like the round one, is necessary for a wide range of designs. When using it, they make:
- fencing;
- furniture;
- railings.
Circle and reinforcement metal A1, if they are made in accordance with specialized standards, are used as raw materials: wire can be drawn from them. Production of profiles is allowed:
If the reinforcing plant has the appropriate equipment, then A1 steel can serve for the manufacture of various products on lathes or milling. The material is machined.
Keeping in mind the standards
Tells what reinforcing steel should be, GOST 5781.82. According to the regulations, carbon in the metal composition can be no more than 0.3%, only then the product is applicable for reinforced concrete. Fittings are used both for previously stressed raw materials, and for ordinary.
If reinforced concrete is used that has undergone preliminary processing and is stressed, then reinforcement is chosen that will cope with quite serious loads inherent in this environment. As a rule, the voltage is quite large, which requires that the metal reinforcement be of increased strength and made strictly of reliable steel. If you use wire, then its strength is also high.
If hot-rolled reinforcing steel will be used in structures not subject to stress, then the use of ordinary raw materials is allowed. The following steel grades are relevant here:
For prestressing, it is customary to take steel with a carbon content:
Steel reinforcement, thermally treated to increase strength parameters can also be used.
Steel: which one?
In order to produce high-quality reinforcing steel, GOST 5781.82 recommends taking reliable steel:
There are several grades applicable for the different types of material mentioned. As a rule, the customer, sending the order to the valve factory, indicates from which raw materials he wants to see the finished product. If the manufacturer does not receive such recommendations, then the manufacturing company independently decides in favor of the best option for a particular type of product. In particular, it is customary to use the following brands for A800:
- 22X2G2AYU.
- 22X2G2R.
- 20X2G2SR.
What else is important?
When creating unstressed reinforced concrete structures , classes from the first to the third should be chosen, and higher ones will be useful if the structure has passed the prestress.
If you have to work at low temperatures, and the object will continue to be operated in extreme conditions, then a reinforcement brand that has a lower percentage of carbon is more suitable. Alternatively, you can choose options for raw materials that have undergone additional processing with high temperature.
But if it was decided to use wire as a reinforcing material, then it is better to give preference to one in which carbon is either completely absent or its content does not exceed 0.8%. This material is characterized by increased strength - up to 180 kgf / mm 2 inclusive. Such parameters are provided:
- high temperature treatment;
- riveted.
Carbon and material quality
Regulates from what raw materials construction reinforcement should be made, GOST 5781-82. In particular, the percentage of carbon has a fairly strong effect on the final parameters of the reinforced concrete product, on its durability and reliability. The more carbon is contained in the metal, the higher will be the hardness inherent in reinforcement, but at the same time, brittleness increases. In addition, it is very difficult to weld high-carbon steel, often the result is not high enough, which affects the reliability of the whole structure.
The percentage of carbon allows you to enter the following classification:
- steel fittings low-carbon, where this connection is contained in an amount of not more than a quarter percent;
- with an average level of content - from a quarter percent to 0.6;
- with a high content ranging from 0.6 to 2%.
How to improve?
In order for reinforcing steel to have better quality, additional components can be added to the alloy. As alloying components it is customary to apply:
- tungsten;
- vanadium;
- chromium;
- nickel.
In some alloys, only one or two additional components are added, in others, a mixture of 5-6 metals. This allows you to get high-quality alloy steel with high rates:
- strength;
- hardness;
- resistance to corrosion.
To obtain alloy steel, you can include silicon, manganese in the raw material. Depending on how many additives are contained in the substance, it is customary to talk about the material belonging to one of the following classes:
- low alloy reinforcing steel containing not more than five percent of inclusions;
- medium-alloyed, in which the amount of additives varies between 5-10%;
- highly alloyed, one tenth or more consisting of additional components.
"What's in a name?"
Reinforcing steel is not just steel, but also a large number of other chemical components. You can find out what inclusions are in the material from the name. Standards have been developed for the designation of certain additives in the name of the material. Examples:
- X is chrome.
- Ts - zirconium.
- T is titanium.
After the mark, the numbers are written. They reflect how much carbon is contained in the material. Hundredths are indicated. Then they write letters. They denote a chemical element, after which it is indicated how much it is contained in the composition of the reinforcement. If no figure is indicated, it can be concluded that this substance is included in an amount of less than one percent.
Example: “reinforcing steel 35GS” stands for steel, which contains carbon at a concentration of 0.35%, and also contains silicon and manganese, but the percentage of both components is insignificant, therefore there are no updated data (they are present in less than a percent of the total amount of material).
What to demand and wait?
According to current standards, reinforcing steel must be:
- easy to weld;
- ductile;
- durable.
Strength is understood to mean the ability of reinforcement to withstand the destructive loads of the external environment. External influences can stretch metal and bend, twist and compress, cut. For each type of load, separate strength indicators are distinguished. Reinforcement is often used in conditions when tensile loads are high, therefore it is this value that should be paid attention in the first place. To assess how much the reinforcement is able to withstand stretching, you need to evaluate:
- fluid limit;
- breaking resistance.
Plasticity is a parameter reflecting the adaptability of the material to external loads trying to change the shape of the product, its cross section. If the reinforcement in these conditions retains its initial parameters, then after removing the load, it can return to its original state or save the changes. Plasticity is expressed in elongation at break, bending angle, the number of bends remaining after cooling the metal.
Weldability is an indicator that reflects the ability to qualitatively connect with other materials when using one or another welding method. This parameter is determined by:
- the composition of the metal;
- smelting method;
- the size of the rods in the context;
- connecting features;
- ductility.
Mechanics and reliability
The above parameters allow us to talk about how good the mechanical parameters of steel are. It is on their basis that technical characteristics and indicators are distinguished.
An important feature of reinforcement is its temporary resistance. To determine it, as well as to reveal how large the fluid limit is, how large the elongation of steel relative to the initial value can be, special tests are carried out in production: tensile testing machines designed for this task are used.
The work is performed as follows: when starting the machine, the load gradually increases on the placed sample. At the same time, the fittings are located in a rigid fastening system that does not allow “slipping” of the specimen. Mechanisms try to lengthen the rod longitudinally, deforming it. The indicators taken from the reinforcement allow you to create a tensile diagram (the scale is set arbitrarily).
Technical features
The straight sections of the diagram reflect such loads at which the sample is not deformed. With increasing loads, you can see a proportional increase in length, allowing us to draw conclusions about the reliability of steel and the ability to resist external influences. The limit value of the load applied to the test specimen is set in advance. Upon reaching this value, the influence of mechanical force is also gradually reduced.
In the best scenario, the rod, which is stretched under the influence of a large external force, returns to its original state when the loads are removed. This ability is due to the elasticity of the steel. It should be understood that the elastic zone for metal has certain limitations. When indicators exceeding these limits are reached, a return to the initial values will become impossible. When identifying such a boundary indicator, one speaks of reaching the elastic limit.
If you test produced in accordance with the current GOST reinforcement made of steel ST3, then you will be able to obtain parameters close to the following:
- yield strength - 2 460 kgf / cm 2 ;
- elongation of 25;
- tear resistance in a given time period - 4,000 kgf / cm 2 .
Parameters and scope
Reinforcing bars with high strength values usually cost more than low quality material. At the same time, practice shows that the use of such material can achieve significant savings, since the reinforcement of reinforced concrete structures requires a more economical consumption of metal.
Pay attention to the plasticity of the reinforcement: there are certain boundaries, which are extremely undesirable to go beyond. By lowering this parameter below a certain level, it is impossible to use rolled products at full strength. A structure made using such a consumable material becomes fragile and can unpredictably collapse under the influence of external factors. There is another risk associated with a decrease in the ductility of the metal: the likelihood of a brittle fracture is already growing at the stage of reinforcing reinforced concrete structures.
Impact on steel samples
To improve the performance of valves, resort to various technologies of exposure from the outside. In particular, the practice of thermal hardening is widespread. At the same time, the strength of the material doubles, and sometimes more. This is most applicable for low alloyed carbon compounds. But the cost of the material is growing by only 10-12%. Thermal hardening shows the best performance relative to mechanical, but for its implementation it is necessary to have serious modern equipment and a team of highly qualified specialists. Very small quality errors of the process influence very much on the quality of the final product (and on the reputation of its manufacturer).
Mechanical hardening is achieved using:
- Winches
- hydraulic jacks;
- profiled rolls.
The latter are needed to flatten steel. During hardening, it is possible to achieve plastic deformations, due to which the strength increases by 50% relative to the initial value.
The most popular is which one?
Traditionally, reinforcement of 8 mm in diameter is most in demand on the metal rolling market. It belongs to the third class and is available in bays, skeins, rods. 8 mm - parameter of the average diameter of the building material. The production of such fittings must comply with GOST 30136-95. Reels produced by coils are called “wire rod” by specialists.
The 8 mm fittings are made of low carbon steel. The brands CT0, CT3 are used. In the manufacturing process, there are two (sometimes one) cooling stages, which allows to achieve high reliability indicators of the material. Rolled wire in coils is a wire.
Fittings A3 - steel having a circle in cross section. It is necessary for the subsequent production of wire, springs. Indispensable raw materials in the production process of construction cold-drawn fittings.
Production and sale
The 8 mm fittings are usually made on wire-grade machines from raw materials complying with GOST 380. This is a standard technology involving the presence of bar steel processed by the shaft system. On machines, the material is rolled and drawn, heated and cooled. Depending on the characteristics of a particular product, it will be cooled naturally or forcefully.
On sale such a product is present both running meters and large coils (for wholesale buyers).
Why is this needed?
The 8 mm reinforcement is indispensable for the construction of reinforced concrete and metal structures. The wire rod is quite thin, so it is used in the manufacture of nets, frames, ropes. The fittings are effective as a basis for staples. It is used to strengthen building structures. A specific option is chosen by analyzing the operating conditions of the building, on the basis of which a decision is made in favor of a particular brand.
Reinforcement is often used as raw material for the manufacture of other construction products, and not as an independent material. If a wire rod is needed to produce nails, cables, then you need to control the evenness of the products: rough surfaces are unacceptable, this will significantly reduce the strength of the finished product. In the manufacture of thick reinforcement, brackets, the requirements for surface smoothness are not so significant. The fittings used to equip the load-bearing walls cannot contain cavities or cracks filled with air. If 8 mm diameter fittings are purchased in rods, quality control involves tracking product identity.
Some features
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Another distinctive moment characterizes the manufacture of steel A800. For it you can apply the following brands:
- 22X2G2AYU.
- 22X2G2R.
- 20X2G2SR.
Moreover, the features of the final product are usually regulated by customer requirements.
According to the recommendations of Gosstroy, in the Russian Federation it is recommended to use the following brands:
Both of them are suitable for hardening reinforced concrete structures and replace the previously widely used A-III. Such are made taking into account the requirements specified in GOST 5781-82.