Rolled steel reinforcement is a set of interconnected steel reinforcing bars designed to strengthen building reinforced concrete products. According to the strength level, the reinforcement is divided into 6 main classes, from AI to AVI - the higher the , the stronger the product. Reinforcing bars of the main classes are produced from low-alloy and carbon steel. Each class of reinforcement corresponds to a specific type of steel for manufacturing:
Class AI fittings (another designation is A240) are made of steel grades St3kp, St3ps, St3sp;
- Class AII (A300) fittings are made of steel grades St5ps, St5sp, 18G2S, 10GT;
- class AIII (A400) fittings are made of steel grades 25G2S, 35GS, 32G2Rps;
- class AIV (A600) fittings are made of steel grades 80S, 20ХГ2С;
- class AV fittings (A800) are made of steel grade 23Х2Г2Т;
- class AVI fittings (A1000) are made of steel grades 22Х2Г2Р, 22Х2Г2АУ, 20Х2Г2СР.
A separate class includes reinforcement used in the construction of especially heavy reinforced concrete structures - these are thermomechanical and thermally hardened steel reinforcing bars. According to the nature of the profile, they refer to the rods of a periodic profile (i.e., grooved rods). Division of reinforcement in class according to the grade of steel used for manufacturing:
At400S – steel grade St3ps, St3sp;
- At500S – steel grade St5ps, St5sp;
- At600 – steel grade 20GS;
- At600S – steel grade 25G2S, 35GS, 27GS, 28S;
- At600K – steel grade 08G2S, 10GS2, 25S2R;
- At800 – steel grade 08G2S, 10GS2, 20GS, 20GS2; 25G2S, 22S, 25S2R, 28S, 35GS;
- At800K – steel grade 35GS, 25S2R;
- At1000 – steel grade 20ХГС2;
- At1200 – steel grade 30ХС2.
The steel reinforcement index may also contain special designations (letters) indicating the quality of the steel:
- letter “t” - thermally strengthened reinforcement;
- letter “c” - reinforcement reinforced by hood;
- letter “k” - reinforcement that prevents cracks from corrosion;
- letter “c” - welded fittings.
Explanation of designations in steel grades
The names of steel grades indicate the composition of the steel or its recommended use. Decoding of the letter designations of the main steel grades: sp - mild steel, ps - semi-mild steel, kp - boiling steel, St - steel intended for structures, S - steel contains silicon, X - steel contains chromium, P - steel composition contains boron, A – the steel contains nitrogen, T – the steel contains titanium. Numerical symbols indicate the percentage of a certain element in the steel composition.
The fittings are a set of interconnected elements that, when working together with concrete in reinforced concrete structures, perceive tensile stresses (beams) and can also be used to strengthen concrete in a compressed zone (columns).
Reinforcement elements are divided into rigid (rolled I-beams, channels, angles) and flexible (individual bars of smooth and periodic profile, as well as welded or knitted meshes and frames). Due to personal interests, in this article I will consider flexible rod reinforcement. Reinforcing bars can be steel, composite and even wood origin (for example, bamboo), etc.
Classification
Reinforcement is classified according to a number of criteria: by purpose, orientation in the structure, conditions of use, and by the type of material from which the reinforcement is made.
The fittings are designed according to their purpose:
working reinforcement (the cross-section is assigned by calculation, it absorbs forces in the elements from the main load)
structural (distribution) (the cross-section is assigned according to the minimum percentage of reinforcement, absorbs shrinkage/expansion, exposure temperature)
mounting (installed to combine working and structural into grids and frames)
anchor (embedded parts)
By orientation in the design:
transverse - reinforcement that prevents the formation of inclined cracks from emerging shear stresses near the supports and connects the concrete of the compressed zone with reinforcement in the tensile zone;
longitudinal - reinforcement that absorbs tensile stresses and prevents the formation of vertical cracks in the tensile zone of the structure.
According to the conditions of use:
prestressed reinforcement;
non-stressed reinforcement.
Prestressed reinforcement in prestressed reinforced concrete structures can only be working.
By production:
-hot rolled rod reinforcement;
Cold drawn wire reinforcement.
In appearance it happens:
Smooth fittings (flat matte surface along the entire length);
Depending on the chemical composition, strength, rolling technology, post-rolling treatment, weldability, corrosion resistance, etc. - reinforcing steel has a certain marking. Reinforcing steel classes are designated as the letter A with an alphanumeric index.
Strength classes of reinforcement (yield strength)
A-I, A-II, A-III, A-IV, A-V, A-VI. Outdated marking according to GOST 5781-82
A240, A300, A400, A500, A600, A800, A1000 - Modern designation.
At400, At500, At600, At800, At1000, At1200 Thermally strengthened construction reinforcement for the manufacture of reinforced concrete products and reinforced concrete products. There is thermomechanically strengthened reinforcing steel, which is used in reinforced concrete factories in the manufacture of prestressed structures and products. For example: prestressed floor slabs.
Additional designations, depending on operational characteristics.
The letter A at the beginning of the marking means that this is a rod reinforcement;
The letter B at the beginning of the marking is wire;
The letter K at the beginning of the marking is ropes;
The letter C indicated after the numbers indicates that this reinforcement can be welded by electric welding. Basically, in private construction, reinforcement cages are knitted with wire. But if electric welding is used, you need to be sure that your reinforcing bars can be welded. For example: A500C fittings;
The letter T indicates that this reinforcement is thermally strengthened;
Letter B - reinforcement reinforced by hood;
The letter K indicated in the class indicates resistance to stress corrosion cracking.
Marking
To conveniently and quickly determine the class of reinforcement, some metallurgical plants apply rolling markings to rods in the form of convex marks on the protrusions; the number of protrusions between the marks means the class of the reinforcement (see figure below). Markings are applied every meter.
If there is no such marking, then identification is provided by the applied paint on the ends or tail parts of the reinforcing bars. Marking colors:
A400C - white;
A500C - white and blue;
A600 - yellow;
A600C - yellow and white;
A600K - yellow and red;
A800 - green;
A800K - green and red;
A1000 - blue;
A1000K - blue and red;
A1200 - black.
And sometimes you come across reinforcement with direct alphanumeric rolling markings on the rod, and even indicating the diameter. In the photo above, for example, A500 C fittings with a diameter of 12 and 16 mm.
Weight of reinforcement and its cross-section
The weight of one linear meter of reinforcing bar directly depends on the diameter (profile number). On the left is a table of the ratio of lengths and weights of reinforcing bars of different diameters in accordance with GOST 5781-82, as well as the cross-section of the reinforcement. It is worth noting that GOST provides for amendments and possible maximum deviations from the data indicated in the table. Depending on the manufacturer’s plant, the GOST ratio of the weight of the reinforcement to its length can range from -7 to + 9%. So, when ordering A500C reinforcement for the foundation from Steel Materials LLC, the manager considered the weight of the reinforcement to be 5% greater than I expected from the reference books, which, however, he immediately warned me about.
What to choose? Practice
For the reinforcement of monolithic strip foundations, periodic profile reinforcement of class A-III (A400) made of steel grades 35GS, 25G2S is mainly used. Such steel reinforcement is a round profile with two longitudinal ribs and transverse projections running along a three-way helical line. The periodic profile of the reinforcement provides better adhesion of the reinforcement to the concrete, in contrast to smooth profile reinforcement, which is recommended for use as strapping (clamps) of longitudinal reinforcement bars. Marking A400 corresponds to the yield strength of this class of steel reinforcement (390 N/mm2). This class of reinforcement is already obsolete. Since the 1990s, European countries have switched to a single class of welded reinforcement with a yield strength of 500 N/mm2. The use of such reinforcement of class A500C instead of reinforcement of class A400 (A-III) provides more than 10% savings in steel in construction. Rebar A-400 and A500C of periodic profile are produced in a domestic version with annular projections (option “a” in the figure above) and in a version with crescent-shaped projections (option “b” in the figure above). The ring profile (a) provides better adhesion strength of the reinforcement to the concrete, and the crescent profile (b) increases the endurance of the reinforcement to periodically repeated loads. For reinforcing foundations, the domestic ring reinforcement profile is better suited. Less common is a four-sided crescent-shaped reinforcement profile, which combines the advantages of both types of periodic reinforcement profile (c).
Reinforcement of class A-III (A400) is not allowed to be connected by welding. When exposed to local temperature, a significant weakening of the steel structure occurs. Structural changes in steel occur in the welding area and in adjacent areas over a length equal to four reinforcement diameters in each direction. Only special weldable classes of reinforcement are intended for welding - A400C, A500C. The American Concrete Institute code emphasizes that welding of cross bars is prohibited, as this may cause the rebar to break. If the class of reinforcement is not known and it is necessary to make a welded connection of longitudinal bars, then the welded reinforcement (45-55% along the length of the bar) must be preheated to 200 °C to minimize loss of steel strength. The minimum length of the weld must correspond to 10 diameters of the rod of the reinforcement being welded.
WITH The most popular diameters of longitudinal working reinforcement in domestic construction are 10, 12, 14 and 16 mm. Transverse mounting - 6.8mm.
When I bought reinforcement for my foundation, I didn’t know anything about what I’m writing now - I just came to the office and ordered reinforcement with a diameter of 12 mm. It’s good that the invoices have been preserved, thanks to which I know that I have A500C reinforcement poured into my concrete, which I’m very happy about! Now we still have to buy fittings and I have already formed some statistical observations in this regard. At metal depots in Brest, fittings with a periodic profile with a diameter of 12 mm are mainly made in Ukraine and mainly of the A500C brand. I personally haven’t come across another one yet. I would recommend it for use in foundations.
Reinforcing bars are in demand in many areas, therefore they are produced in a wide range. Each manufacturer is required to apply certain markings to their products, which reflect the physical and mechanical properties and performance qualities of the products.
What is fittings needed for?
Concrete is not in vain considered one of the strongest and most durable building materials. It can withstand compressive loads well, but weakly resists tensile or shear loads. Because of this, the structure can quickly crack or break.
To improve quality characteristics, reinforced concrete has been used for many years. This is a kind of alloy of metal and artificial stone. First, a frame of steel rods is formed in the formwork -. And then the concrete is poured. The resulting structure has all the necessary set of properties: strong, yet quite plastic, and can withstand almost all types of deformation loads, including vibration, bending, and the like.
The description of construction reinforcement will be incomplete if we do not list the areas of use of steel products. This:
1. Construction of residential low- and multi-storey buildings (foundations, monolithic walls, ceilings), industrial buildings, complex special-purpose structures (berths, hydroelectric power stations, subways).
2. Construction of various supporting and protective structures (greenhouses, pipeline supports, columns).
3. Installation of screed, strengthening of plaster.
4. Production of shaped reinforced concrete products (rings, pipes, floor slabs, beams, foundation blocks).
5. Formation of road surfaces, sidewalks, airfield runways, etc.
For each of the above areas, fittings of a certain grade, type and diameter are produced. These parameters are indicated as an alphanumeric character set on each rod.
Reading the marking symbols
The symbolic code for reinforcing bars begins with the letter:
- A – hot-rolled or cold-rolled (heat-strengthened) products;
- B – cold-deformed;
- K - ropes.
The following series of reinforcing bars are distinguished:
1. A240 or A1 – made from steel grades St3SP, St3PS, St3KP, classified as mounting rods with a smooth profile with a diameter of 4 to 40 mm.
2. A300 or A2 – made of metal of the ST5SP(ps) or ST18G2S series, refers to work products with a corrugated surface with a cross-section of 10-80 mm. Depending on the diameter, it is produced in the form of wire, rolled into coils or rods 6-12 m long.
3. A400/A500 or A3 – produced from steel grades 35GS, 25G2S, 32G2R. This is a working reinforcement of a periodic profile with a cross section of 6-40 mm. Also produced in the “B” series from metal using the cold drawing method. This is the most popular reinforcement for slab, strip or pile type foundations.
4. A600 or At4 - made from low-alloy heat-strengthened (cold-rolled) steel of class 80C, 20ХГ2Ц, intended for welded structures. The length of the rods is classified as measured (rods of 6, 9 and 11.7 m) or unmeasured (rods and coils up to 12 m). The diameter varies from 10 to 32 mm. The surface is periodic, crescent-shaped.
5. A800 or At5 - made from low-alloy metal raw materials of grade 23Х2Г2Т. The products are produced in diameters of 6-40 mm and are intended for the formation of welded frames in conventional and prestressed concrete products.
6. A1000 or A6 - from low-alloy steel of classes 22Х2Г2АУ, 22Х2Г2Р and 20Х2Г2СС. A distinctive feature is the use of any type of welding work without restrictions. The diameter of the rods varies from 6 to 32 mm.
The marking also includes an indication of the special properties of the product:
- K – corrosion resistance. Products undergo galvanizing, galvanizing and other processes, as a result of which a protective film is formed on the surface to prevent oxidation.
- C – connection by welding.
- T – thermomechanically hardened steel.
After the main parameters, the diameter is indicated. For example, the marking A500C Ø12 stands for hot-rolled reinforcement with a fluidity index of 500 MPa and a periodic profile, intended for welding work, the diameter of the product is 12 mm.
For certain types of products, GOST standards require that the ends of the rods be painted. The following colors are used for different classes:
1. For low-alloy steel fittings:
- A4 – red;
- A5 – red and green;
- A6 – red and blue.
2. For rolled heat-strengthened metal:
- At3 – white and blue;
- At4 – white and yellow;
- At4K – green;
- At5 – blue;
- At5SK – white and green;
- At5K – yellow and green;
- At6 – yellow;
- At6K – green and black.
Color marking complements the alphanumeric marking and provides additional information about the product.
To make shutoff valves convenient to classify, store and sell, they are marked and designated in a certain way. At the same time, the marking of shut-off valves, on the one hand, should not take up much space on the product, on the other hand, it should be as informative as possible for the consumer and manufacturer. Today, all existing types of domestic shut-off valves are marked in accordance with Russian legislation (GOSTs).
Marking of shut-off valves must include:
Trademark or manufacturer's name;
nominal diameter, mm. Here we mean the conditional (nominal) diameter. It is designated as DN (DN), followed by the diameter value without a space;
conditional pressure, MPa. Nominal pressure. Designated as Ru or PN. In addition to pressure, it is possible to indicate the operating temperature range;
direction of the medium flow. Indicated by an arrow on the body. It is applied at the stage of casting and stamping;
brand of body material. The materials of the body and shutter are marked as follows: NZ – stainless steel, LS – alloy steel, h – gray cast iron. Sealing surfaces: br - bronze, brass, p - plastic, p - rubber.
How are shut-off valves marked?
In accordance with domestic GOSTs, the marking of shut-off valves is applied directly to the product body. All information about a specific model is applied on the front side, and the manufacturer’s mark is on the back. Marking of shut-off valves on the metal surface of the body is applied in three main ways:
stamping. Represents the process of deformation of a material. This embossing creates letters and numbers on the surface of the valve body. The durability of this embossing is the same as that of the reinforcement itself;
engraving. It is one of the oldest methods of applying inscriptions to metals. Engraving can be found on pre-revolutionary valves and taps. Letters and numbers are applied using a cutter, which can be a graver, a milling cutter, or a punch (looks like a nail);
branding. It is a rather complex process that will require certain skills and professionalism from the performer. For application, special equipment is used - an electric spark pencil. This method is used quite rarely.
It should be noted that, depending on the material of the body parts, the outer surfaces of the shut-off valves can be painted in the appropriate color:
blue painting means alloy steel;
blue – corrosion steel;
black paint color corresponds to gray malleable cast iron;
gray – carbon steel.
Let us describe the marking of shut-off valves using the example of products from the Admiral plant:
19s63nzh. The number 19 means a non-return valve, a sealed valve. The small letter "c" means the body is made of carbon steel. The letters “NZ” indicate that the sealing surfaces in the product are made of stainless steel;
30nzh541nzh. “30” means that the shut-off valve is a gate valve type. “NZH” – the body is made of stainless steel. “5” means that the control method uses a mechanical control method with a bevel gear. “41” is the model number. “NZH” – the sealing surfaces in the product are made of stainless steel;
32s908r. “32” – the product is a butterfly valve. “c” – made of carbon steel. “9” – controlled by an electric drive. Model number 08. “p” - sealing surfaces are made of rubber.
The Admiral plant pays due attention to the marking of shut-off valves. Moreover, this is done not only to make life easier for the consumer and operator of the product, but also to make it easier to store products in the enterprise’s warehouses and distribute them to representative offices and sales points. Markings allow easy classification of fittings.
Clear, clearly visible markings on shut-off valves make handling them simpler and more convenient. This applies to both purchase and delivery, as well as further maintenance, repairs, and the purchase of spare parts for it. Poorly visible markings can ultimately lead to incorrect replacement of the part and complete failure of the product.
Marking of shut-off valves is applied at the final stage of production, but before testing procedures. If a defect is detected, the model will not be lost and will be quickly modified (corrected). Marking is applied by qualified specialists using modern equipment. Quality labeling is a sign of good reputation and responsibility of the manufacturer.
Most concrete structures require reinforcement using special products. They take on the main share of the tensile load. The marking of the fittings, which encodes the main technical characteristics, will help you choose the right material according to the calculation results.
Classification
Depending on their scope:
- for the construction of residential and industrial buildings of various heights (strengthening the foundation, monolithic walls, ceilings), berths, complex hydraulic and underground structures;
- for installation of supporting and enclosing structures (columns, greenhouses, pipeline bases);
- for the manufacture of screed, durable plaster;
- for the production of various reinforced concrete products (pipes, panels, collector rings, floors, foundation and wall blocks);
- for laying sidewalks and creating road surfaces.
For each category, reinforcement is designed from a material of appropriate strength, type and size. It is customary to mark products using an alphanumeric code; the ends of the rods are painted in certain colors. Symbols simplify control over the sale and use of reinforcing products.
The following characteristics can be encrypted in the marking:
- material – steel or polymer composite (based on basalt or fiberglass);
- purpose – working, distribution, installation;
- section profile – constant or periodic;
- execution - ropes, rods, wire;
- installation method - knitted or welded.
Steel rods are popular; such reinforcement is divided into corrugated and smooth. The first of them has a variable (periodic) diameter value due to notches. Corrugated (ribbed) combines several subspecies: with an annular, crescent-shaped, mixed profile. Such products are produced in compliance with geometric and physical parameters: the angle of inclination and height of the protrusions, the pitch between adjacent notches, the equivalent cross-sectional area, and the yield strength norm. Smooth reinforcement is characterized by a constant diameter.
Classes and markings
Several technical standards have been developed containing descriptions of construction reinforcement. Each of them has its own notation system.
1. GOST 5781-82 “Hot-rolled steel for reinforcement of reinforced concrete structures.”
In accordance with this standard, reinforcing bars are classified according to the chemical composition and physical properties of rolled steel. The breakdown of fittings by class is given in the table.
| Strength class (old marking and its equivalent according to European standards) | steel grade | Yield strength, MPa | Circle diameter, mm | Description |
| A-I (A240) | Carbon St3KP, St3PS, St3SP | 240 | 4-40 | Smooth |
| A-II (A300) | Low alloy St18G2S or carbon St5SP, St5PS | 300 | 10-80 | Corrugated, produced in the form of rods (6-12 m) or wire rolled into a coil |
| A-III (A400) | Alloyed 35GS, 25G2S, 32G2R | 400 | 6-40 | Ribbed reinforcement for foundation |
| A-IV (A600) | Low alloy cold rolled 80С, 20ХГ2Ц, | 600 | 6-40 | Corrugated crescent-shaped, for welded frames of reinforced concrete products |
| А-V (A800) | Low alloy 23Х2Г2Т | 800 | 6-40 | Ribbed, for welding frames in reinforced concrete products |
| A-VI (A1000) | Low alloy 22Kh2G2AYu, 22Kh2G2R and 20Kh2G2SR | 1000 | 6-32 | Corrugated, for welding work |
To inform the consumer about the special properties of metal products, manufacturers additionally label them:
- K – corrosion-resistant steel with a protective coating (galvanized, galvanized);
- C – allows connection by welding;
- T – thermomechanically strengthened rolled products.
After the main data, indicate the diameter of the rod. For example, A600C Ø18 stands for: cold-rolled reinforcement with a yield strength of 600 MPa, intended for a welded reinforced concrete frame.
The reinforcement is packaged in coils or bundles, fixed with wire. Each bundle is marked: a tag with a symbol is attached. For classes A600-A1000, color marking of the ends of the rods with paint is used:
- A600 – red;
- A800 – red and green;
- A1000 – red and blue.
2. GOST 10884-94 “Thermomechanically strengthened fittings”.
This standard formulates requirements for the most critical types of reinforcing products designed for increased loads. To increase their strength properties, they are subjected to thermomechanical treatment. Classification is carried out depending on the following properties:
- a standardized yield strength indicator, which is determined by the chemical composition of the material;
- performance qualities - weldability (letter index C), resistance to corrosion cracking (letter K), weldability with anti-corrosion resistance (SC).
The fittings manufactured according to GOST 10884-94 are divided into classes:
- At400 – from rolled carbon steel St5;
- At500S, At600 – from low-alloy steel grades 20GS; 25G2S; 35GS; 28C; 10GS2;08G2S;25S2R;
- At800 – from low-alloy steel 20GS; 20GS2; 08G2S; 10GS2; 28C; 25G2S; 35GS; 25С2Р; 20ХГС2;
- At1000, At1200 – from rolled steel 30ХС2.
3. GOST 31938-2012 “Composite reinforcement for reinforcing concrete structures.
It is customary to mark non-metallic reinforcing products according to the type of filler. According to this classification, the following types are distinguished:
- ASK – with fiberglass;
- ABK – with basalt fiber;
- AUK – carbon composite;
- AAK – aramidocomposite;
- ACC – combined.
Diameters vary from 4 to 32 mm, their profile is ribbed. Product marking includes: type of reinforcing bars, diameter, limiting tensile pressure, tensile modulus of elasticity, GOST. For example, basalt-composite reinforcement with a diameter of 10 mm with a tensile strength of 1000 MPa and an elastic modulus of 50 GPa is designated as follows: ABK-10-1000/50 - GOST 31938-2012.
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