Thermo-mechanically treated (TMT) bars are preferred for construction projects because of their enhanced strength, high ductility, workability, and malleability. TMT bars are, in fact, originally designed to support buildings during earthquakes and to resist high temperatures, especially during fires. However, TMT bars come in various grades, which represent a range of rigidity and strength.
All TMT bars are good for construction, but their different steel grades suit different types of structures. Fe 415 TMT bars are good for houses, Fe 500 are ideal for commercial buildings, Fe 550 are for bridges and other slightly large-scale structures, and Fe 600 are for big industrial projects.
This article will talk about the different grades of TMT bars in more detail, including their yield strength, tensile strength, elongation, and the types of construction projects that are most suitable for each of them.
The Different Grades of TMT Bars
TMT bars are steel bars that have gone through a process of rapid cooling while in their molten state. This gives the steel bars a pliable core but with a hard and solid surface. Their outer shell has a film coating that protects them from rust and corrosion and this, in turn, makes them great materials to use in building structures like bridges and high-rise residential buildings in humid places.
To rapidly cool the TMT bars, water is sprayed at regular intervals. However, these intervals differ, giving the steel bars different steel grades. These grades are defined by different characteristics, including different rigidity levels and yield strength of reinforcement.
The different grades of TMT bars are:
- Fe 600
- Fe 550
- Fe 500
- Fe 415
The lowest grade is the Fe 415 bar, and the highest is Fe 600. Fe stands for iron.
These bars are graded according to the amount of yield stress that they can withstand safely and without irreversible deformation. When stress is applied within its yield point, the bar will deform elastically, but it will return to its original form or shape when this stress is removed. The higher the steel grade of the TMT bar, the less bendable it is.
This yield strength is measured in Newtons per square millimeters or N/mm². For instance, a Fe 550-grade TMT bar provides a yield strength of 550 N/mm². Beyond that and the bar may no longer be able to maintain its form.
The Fe 415 are TMT bars with a yield strength of 415 N/mm² and an ultimate tensile strength of 485 N/mm². Its elongation is 14.5 percent.
These steel bars are typically used in building houses, residential structures, and small-scale construction projects because of their high uniform elongation. This characteristic makes them resistant to earthquakes, too. As such, they are perfect for building homes in areas that are prone to seismic activities.
These TMT bars also benefit from a protective coating that makes them resistant to corrosion and rust. It can be easily bent into the most complex shapes, too.
This TMT bar has a minimum yield strength of 500 N/mm² and an ultimate tensile strength of 545 N/mm². Its elongation is 12 percent.
The Fe 500 is called a market-standard as you can use it across a wide variety of construction projects. This bar has been used in the construction of commercial structures with multiple stories, smaller bridges, and underground structures. It offers stability to high-rise construction projects and, at the same time, resists load better.Moreover, this grade of TMT bar is commonly used in coastal areas because of its anti-corrosion properties.
Fe 550 grade TMT bars have a minimum yield strength of 550 N/mm² and an ultimate tensile strength of 585N/mm². It has a 10-percent elongation level.
Because these steel bars have higher tensile strength than the Fe 500, they can be used in a broad range of large-format, high-load capacity, and industrial infrastructure development projects like heavy bridges and underground structures.
These TMT bars are especially impactful in marine and coastal environments, too.
Fe 600 TMT bars boast a yield strength of 600 N/mm² and an ultimate tensile strength of 660 N/mm². Their elongation is 10 percent. These bars are the strongest steel bars available in the market and are used for large-load, heavy-duty industrial construction projects. Examples of such construction projects are metro projects, expressways, towers, plants, industrial zones, and huge commercial properties.
Why Use TMT Bars for Construction?
Cold-twisted deformed bars were used extensively for reinforcement in construction before TMT bars came into the picture and ruled the market. TMT has effectively taken over the low-cost reinforcement bars industry because CTD technology was plagued with certain problems, including inferior ductility, higher carbon content, low weldability, and increased corrosion rate.
You should note, however, that not all TMT bars are created equal. Quality still varies across brands. And when looking for the best quality TMT bars, you need to take note of the following characteristics:
- They come with the perfect balance of flexibility and strength, even with low carbon content.
- They have higher yield strength, high ultimate tensile strength, and a higher elongation percentage when compared to CTD bars of the same grade.
- They are highly weldable and, therefore, you can use them for a wide variety of purposes.
- They are highly resistant to earthquakes and corrosion.
- They contain a much lesser amount of sulfur, which makes the structures fire-resistant.
Choosing the Right TMT Bar
According to Build Supply, the most crucial aspect of getting the correct TMT bars comes down to whether high-quality brands are available. The right brands deliver premier quality for their TMT bars.
What’s more, these brands emphasize protocols for international-standard testing and monitoring to ensure that they provide consistent products for your construction projects. They’re also transparent in terms of pricing, which, in turn, helps you decide in a streamlined and expedient manner.
Shyam Steel points out that the best TMT bars can protect a structure from fire, absorb extra energy in the event an earthquake happens, and can resist corrosion.Moreover, TMT bars have gone through a variety of tests to check the quality of various properties.
- Flexibility and bendability: These are high-strength bars, so they should have gone through a bend and re-bend test. In this test, TMT bars are bent to 135 degrees and are kept submerged in boiling water for around half an hour. It is then re-bent to around 157.5 degrees. Bars that are manufactured with the right combination of strength and flexibility should be able to bend easily but without cracks on the surface along the bends.
- Strength: The strength of the bars is tested using a Universal Testing Machine. A TMT bar is positioned in between the UTM’s plates and pressure is applied to make sure it does not break before the yield point.
- Chemical composition: The chemical composition of the TMT bars has to comply with the IS Specification. This chemical makeup needs to be right in order to produce steel bars that are of the correct grade. A spectrometer is used to measure this chemical composition.
Whatever your core construction project requirements and specifications are, and whatever quality standards you are applying, one thing is certain: you have to use the right TMT bars. Not only do you need to get TMT bars from the best manufacturers to ensure superior quality, but you also need to make sure you get the right grade of TMT bars for your specific construction project.
All TMT bars can be used for construction, but different grades have different levels of strengths and bendability. And different types of construction projects and structures need different stress strength. As such, it is important to use TMT bars that can provide the best amount of support for your structure, given its size and its capacity.
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