Notes on Reinforcing Steel

Reinforced steel, commonly known as rebar (short for reinforcing bar), is an alloy of ferrous metal with 0.25 to 1.5 percent carbon. The higher the carbon content, the harder the steel. Steel bars of circular cross-sections are mainly used as reinforcement to strengthen concrete structures. There are three types of reinforcing steel:

1. Mild steel
2. High Yield Strength Deformed bars (HYSD)/TOR steel and
3. High tensile steel.

High-Yield Strength Deformed Steel Bars. Image Source: Wikimedia (W.carter)

1. Mild Steel

Mild steel contains carbon at levels of 0.23 to 0.25%. A higher value is permitted for bars with a diameter of 20 mm or greater. 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 rib deformations on their surface, which improve the bond between the concrete and steel. 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 phosphorus. The process of making these wires involves cold drawing and tempering. They are usually available in 2, 3, 4, 5, 6, 7 mm diameters. They may be bundled together in groups to form a strand. These bars have tensile strengths ranging from 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.

Reinforcing steel is a fundamental material in construction that significantly enhances the strength and durability of concrete structures. Its various types and applications ensure that it meets the diverse needs of modern engineering and construction projects.