Steel is an alloy of ferrous metal with 0.25 to 1.5 percent of carbon. The higher the carbon content, the harder is the steel. Steel bars of circular cross-sections are mainly used as reinforcement to strengthen concrete structures.
There are three types of reinforcing steel:
- Mild steel
- High Yield Strength Deformed bars (HYSD)/TOR steel and
- High tensile steel.
1. Mild Steel
It contains carbon up to 0.23 to 0.25%. A higher value is permitted for bars of 20 mm and above diameter. It is available in diameters of 6, 10, 12, 16, 20, 25 and 32 mm. Its yield strength is 250 N/mm2 and young’s modulus 2 × 105 N/mm2. It was a very commonly used reinforcement in concrete. But nowadays TOR steel is replacing it. It is used as window bars, for grills and for making steel gates.
2. HYSD Bars/TOR Steel
Two types of TOR steel bars are available. They are Fe-415 and Fe-500. The number associated with the designation indicates the tensile strength of the bar in N/mm2. These bars are provided with ribs deformation on the surface so that the bond between concrete and steel improves. These bars are available in diameters 8, 10, 12, 16, 20, 22, 25, 28 and 32 mm. Nowadays these bars are replacing mild steel bars as reinforcement since their strength in tension and bond is higher. These are also used as wind bars.
3. High Tensile Bars
High tensile steel bars are made with 0.8 % carbon and 0.6 % manganese apart from small percentages of silicon, sulfur and phosphorous. The process of making these wires involve cold drawing and tempering. They are usually available in 2, 3, 4, 5, 6, 7 mm diameters. They may be bundled with the number of them to form a strand.
These bars are having tensile strength as high as 1400 N/mm2 to 1900 N/mm2. The young’s modulus of steel is also the same as that of mild steel.
High tensile bars are used as reinforcement in prestressed concrete.