Reinforcing steel is also called reinforcing iron or rebar, and reinforcing steel is the material used in concrete to increase the flexural strength of the concrete element.
In the past, before the invention of reinforcing steel, various techniques were used to absorb tensile stresses caused by loads or the structural shape was changed so that tensile stresses did not occur.
The best example is the bow. It was used as a compression element that absorbs loads as compressive loads or as axial pressure.
The use of rebar in masonry construction dates back to the 15th century. Originally they were mainly used in masonry to increase their load capacity. The turning point in the use of rebar in civil construction occurred in the 19th century, when its resistance was increased through embedding in concrete.
Improving the strength of reinforcing steel becomes even more popular as it can become strong R Reinforced concrete elements.
Why reinforce steel in concrete?
Concrete is strong in compression and weak in tension. In general the tensile strength of concrete is about 10% of its compressive strength .
When concrete is subjected to bending stresses, pressure and tension are created in the section. The tensile stress is supported by the reinforcement and the concrete supports the compressive stress.
If the concrete cannot withstand the axial tension, we also add reinforcing steel to absorb the compensation tension.
Development of steel reinforcement technology
Previous steel did not have the strength of the rebar we use today. We now have reinforcements with a strength of 500-6000 N/mm 2 .
The following table shows the development.
| Bar type | Introductory year | Yield limit/MPa |
| Simple round | 1895 | 230 |
| Deformed | 1920s | 230 |
| Twisted square | 1957 to 1963 | 410 |
| Deformed intermediate quality | 1960 to 1968 | 275 |
| Deformed hard quality | 1960 to 1968 | 345 |
| Twisted deformed | 1962 to 1983 | 410 |
| Hot rolled and deformed (410Y) | 1983 | 410 |
| Hot rolled and formed (400 years) | 1988 | 400 |
| Hot rolled and formed (500 years) | 2000 | 500 |
There are four main types of rebar used in construction today.
- Structural steel
- steel gate
- TMT Steel
Properties/characteristics of reinforcing steel
As mentioned previously, there are three main types of rebar used in construction. We characterize these steels based on their strength.
The yield strength or yield strength of 0.2% is used to characterize the reinforcing bars. Consequently, the following categorization is based on yield strength.
| Type of reinforcement | Yield limit / N/mm 2 |
| Structural steel | 250 |
| steel gate | 460 |
| TMT Steel | 500/550/600 |
Let's look at the main difference between TMT steel and TOR steel.
Difference Between TMT Bars and TOR Steel
- tensile strength
TMT bars have a higher yield strength than TOR steel, as shown in the figure above.
Increasing the yield strength reduces the area of reinforcement to be used and leads to reduced construction costs.
- Ductility
Ductility is the ability to withstand greater loads without failure.
Due to their inherent properties, TMT bars are more ductile than TOR steel.
- renovation
TMT bars exhibit greater elongation due to their cross-sectional properties. The hard outer layer and soft inner layer allow it to stretch without breaking.
- Weldability
The low carbon content in TMT rods allows welding without changing material properties. Furthermore, the hard outer layer withstands the temperature rise during welding.
Chemical composition of reinforcing bars
To check the chemical composition of reinforcing steel, the carbon equivalent value is mainly used as the characteristic value.
Ceq = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15
The following applies: Mn – percentage of manganese content, Cr – percentage of chromium content, V – percentage of vanadium content, Mo – percentage of molybdenum content, Cu – percentage of copper content and Ni – percentage of nickel content.
The following table from BS 4449 gives the allowable carbon equivalent value for casting analysis and product analysis.
Let's also look at a comparison with other standards. Compared to BS 4449, ASTM allows different values.
The following table, taken from the technical document, gives a clear indication of the distribution of values.
Reinforcement sizing
The standard diameter and cross-section specified in the flow table in accordance with BS 4449:2005 shall be used in calculating quantities or design requirements.
The remaining mass must be calculated according to the table.
| Nominal diameter/mm | Cross-sectional area/mm 2 | Mass per meter/kg |
| 6 | 28.3 | 0.222 |
| 8th | 50.3 | 0.395 |
| 10 | 78.5 | 0.617 |
| 12 | 113 | 0.888 |
| 16 | 201 | 1.58 |
| 20 | 314 | 2.47 |
| 25 | 491 | 3.85 |
| 32 | 804 | 6.31 |
| 40 | 1257 | 9.86 |
| 50 | 1963 | 15.4 |
Permissible tolerances for reinforcing steel – BS 4449:2005
- length
The allowable deviation from the nominal length is +100/-0mm .
This means that the length can be increased by 100 mm, but the specified length cannot be reduced.
- Dimensions
The permissible deviation from the nominal value Mass per meter must be no more than ±4.5% for a nominal diameter greater than 8 mm and no more than ±6% for a nominal diameter less than or equal to 8 mm. .
However, there are small deviations in the values according to other standards, as shown in the following figure.
- Surface geometry
The arrangement of the ribs and their dimensions and angles shall be as specified in BS 4449. These have been discussed in the Reinforcement Rib article For further information you can contact us.
Reinforcement Bar Test
Two main types of tests are performed for reinforcement. The sequence of booster tests depends on the relevant standards.
- Check the chemical composition – Chemical analysis of steel bars
- Check physical properties – strength and elongation
To maintain the quality of reinforcement in production and on the construction site, continuous checks and tests are carried out.
BS4449:2005 specifies the following inspection criteria/rates for bars and rolls.
- Chemical composition: One analysis per test unit and casting analysis should have been carried out by the steel producer
- Bending tests, nominal mass per meter and surface geometry : one specimen per specimen and nominal diameter.
- Tensile tests : one specimen for every 30 tons with at least three specimens per test unit and nominal diameter.
Chemical Composition – Chemical Analysis of Reinforcing Steel/Casting Analysis
As discussed previously, we check the chemical composition of the steel and calculate the carbon equivalent value.
In these tests, chemical analyzes are carried out on all types of rebar. The order of testing depends on the relevant standard or design specification.
This test is typically performed for one analysis per test unit.
Chemicals like C, Si, Mn, P, S, Cr, Mo, Ni, Cu, V etc. are checked and the carbon equivalent value is determined based on the corresponding chemicals as shown at the beginning of the article. When the created analysis is completed, it should be below 0.52.
The maximum chemical levels established for product analysis; Carbon ( 0.24 ), sulfur ( 0.055 ), phosphorus ( 0.055 ), nitrogen ( 0.014 ) and copper ( 0.85 ) are checked in addition to the carbon equivalent value.
Physical properties
It is essential to check the physical properties of reinforcement during production and construction.
Essentially, three types of tests are carried out on the sample taken from the reinforcement brought to the construction site.
- tensile strength
- Back bend test
- Rib geometry
tensile strength
The following parameters are tested under tensile properties
- Stretch limit
- tensile strength
- Percentage elongation
- Cross-sectional area
- Mass per meter of length
Checks whether the above parameters are within acceptable limits, as explained in the first part of this article.
There are different types of reinforcements
Types of rebar
- European reinforcing steel
- Carbon Steel Reinforcing Steel
- Rebar coated with epoxy resin
- Galvanized reinforcing steel
- Glass fiber reinforced plastic (GRP)
- Stainless Steel Reinforcing Steel
The following articles refer to concrete reinforcement. It's worth reading to find out more.
Removing rust from steel reinforcement – a practical approach
All about mechanical clutches
