What is tmt bars?
TMT bars are a kind of reinforcement bars. It stands for Thermo mechanically treated bars. There are Different types of TMT bars which are the hot rolled bar of varying diameters used as tension bars in concrete to strengthen its tensile strength of the concrete.
TMT bars are high strength and high ductile bar having 2 layers. The outer layer is hardcore and the inner core is softcore. In general, the strength of reinforcing bars can be increased by cold twisting, microalloying, thermomechanical treatment, and increasing carbon content.
These rebars undergo thermomechanical treatment which refers to a series of processes.
- Quenching: Quenching is a kind of surface treatment of steel. In quenching steel is rapidly cooled through water, air, or oil. Quenching makes the surface of steel hard.
- Self-tempering: Tempering is a process of making the steel ductile. The inner core of the bars is still hot, so allowing heat to flow from core to surface.
- Atmospheric Cooling: In this phase, bars are let cool under atmospheric temperature. This process increases the tensile strength that makes it weldable and ductile.
Features of TMT bars
- Enhanced ductility and malleability.
- They are more resistant to rust.
- Improved thermal resistance
- Weldable and no loss in strength during welding due to low carbon content.
- They have high bonding strength with concrete.
- They provide high yield strength and toughness
- They are economically safe in use.
Different grades of TMT bars | Different types of TMT bars
There are 9 grades of TMT bars available. According to the IS 1786, the maximum value of the metals and non-metals allowable during the manufacturing of TMT bars are tabulated below.
|Chemical Properties||Maximum Value|
|Sulphur and Phosphorous||0.110||0.105||0.1||0.075|
|Mechanical properties||Minimum Value (MPa)|
|Tensile Strength||1.25*yield strength||545||585||600|
General Uses of different grade of tmt bars
- Fe 415, Fe 415D
They give yield strength of 415 N/mm2 and Tensile strength not less than 485 N/mm2 . They have higher uniform elongation make these bars suitable for earthquake prone zones. They are also resistant to rusting.
- Fe 500, Fe 500D
They are also used in normal residential buildings but are more preferred in bridges and multiple stories, underground structure. Fe 500 give high corrosion resistance, excellent bendability and great resistance on dynamic loading.
- Fe 550, Fe 550D
They give slightly more yield strength and tensile strength. They are basically used in coastal areas, marine area and underground structures.
- Fe 600
These bars are used where high tensile strength is required.
After all choice of grade of steel is all about the owner and requirements of site condition.
I hope this article on “Different types of TMT bars” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rukshana Shresth