TMT Steel Bar is a common construction material. The TMT Bar is made from the Raw materials like iron ore, coal, and dolomite. The use of Steel Bars in the construction industry is done for various purposes including building and building components, bridges, RCC roads, towers, and many more. The TMT bars are most preferably added in combination with concrete to provide tensile strength in concrete.
The reinforcing steel (TMT Bars) absorbs the tensile, shear, and sometimes the compressive stresses in a concrete structure. Plain concrete doesn't handily endure ductile and shear stresses brought about by wind, earthquakes, vibrations, and different forces and is subsequently unsatisfactory in most construction applications. In reinforced concrete, the elasticity of steel and the compressive strength of concrete work together to permit the part to support these worries about longer spans.
How TMT Steel bars came into origin?
Introduced in 1979 complying with IS 1785:1979, TMT bars came with Grade Fe 415, Fe 450. In 1985, a higher grade of these bars – Fe 500 (IS 1786:1985) was introduced in the market and since then the demand for TMT bars has only risen in the Indian construction industry. 2008 saw the introduction of Fe 600 grade TMT bars confirming to IS 1786:2008.
TMT bars or Thermo-Mechanically Treated bars are high-strength reinforcement bars having a tough outer core and a soft inner core. The absolute initial step of the assembling process includes passing the steel wires through a rolling mill stand. From that point, these rolled steel wires are again gone through the Tempcore water cooling zone. While passing the wires through the water cooling zone, the water pressure is optimized. The sudden quenching and drastic temperature change harder the external layer of the steel bar, thus making it super tough and durable. Once this process is over, the TMT bars are left in the open air to get cooled. This is done to equalize the temperature difference between the soft inner core and the tough exterior. When the TMT bar cools, it gradually transforms into a ferrite-pearlite mass. The internal core’s remaining softs give the TMT bar extraordinary rigidity and prolongation point. This plan is exceptional to the TMT bars and gives better flexibility to the bars. Likewise, this remarkable assembling procedure and the shortfall of cold stress make this bar erosion safe and increases its weldability.
What are the different Types of TMT Bars used in the Construction Industry?
1. Fe415 Steel
Fe 415 TMT is being used for small-scale construction projects as they provide cost-effectiveness and ductility. Perfect for small load constructions as they can be easily bent into the most complex shapes.
– For reinforcing residential homes, houses, and small-scale structures.
– Because of the uniform elongation property these types of bars can be used in the place where the area is prone to earthquakes.
2. Fe 500 grade -
Fe500 grade is remarked as a market standard across many construction projects. Variations in Fe500 are Fe500D and Fe500S, which are also popular choices that offer greater seismic stability and ductility.
– Fe500 bars can be used across a range of residential, commercial, and multi-story projects.
– They offer greater tensile strength and greater ductility than Fe415 which are specially manufactured to provide stability to high-rise projects while resisting load better.
– These bars are used in the areas where there are high seismic activities and sudden loads.
3. Fe500D grade –
These types of bars are similar to the Fe500 grade but the letter ‘D’ denotes Ductility. These have higher ductility than normal Fe500 grade bars. These bars have lower percentages of Sulphur and Phosphorus to get the properties they are named after. This feature provides the Fe500D TMT bars with the capacity to absorb sudden loads.
- These bars are ideal for various natural disasters like earthquakes, tsunamis, and cyclones. The high security highlights presented by Fe500D TMT bars make them appropriate for zones having high seismic movement.
4. Fe550 grade –
Due to greater tensile strength, Fe 550 grade bars can be used across a range of large-scale projects.
– These are used for developing industrial and large-format infrastructure projects like bridges, industrial projects, and structures requiring high load-bearing capacities
– These bars are especially concentrated in coastal, marine, and underground environments.
5. Fe550D grade –
Similar to Fe500D grade bars, Fe550D bars are also better in ductility than Fe550 bars. Lower quantities of carbon, sulphur, and phosphorous, in these bars, help in preserving the steel and resisting earthquake shocks in the future. The enhanced mechanical properties of the ‘D’ grade TMT bars allow elevated resistance of the bars to natural calamities and also better resistance under stress. These bars also have good weldability due to the low percentage of carbon in them.
Fe550D bars are used in areas where Fe550 grade bars are used but are under zones with high risks of natural disasters.
6. Fe 600 grade –
Fe 600 is one of the most grounded TMT grades utilized growing uncompromising foundation projects, spans, marine offices, and so forth. They offer more prominent elasticity, reduce overall utilization, and guarantee lesser steel blockage inside the reinforcement.
– Fe 600 are utilized in the development of expressways, metro projects, towers, business properties, and industrial zones.
- Broadly utilized for an enormous scope of projects where the more spotlight is on load-bearing, solidness, and resistance to corrosion.
Chemical Compositions of Different TMT Bars (In %)
What are the IS Codes for TMT Bars?
There are different types of TMT Bars available in the Indian market, with their respective cross-sectional areas. Each type of bar with a specified cross-sectional area has a different application than the rest. Therefore, it becomes necessary to know which type of bar is apt for certain construction work or not. Therefore, the Bureau of Indian Standard (BIS) has some IS Codes for practice and references for all types of reinforcement bars. Below are the IS Codes that are recommended for reinforcement detailing and guidance.
- IS:432- 1982: Mild steel & medium tensile steel bars and hard drawn steel wires for concrete reinforcement: Part-II -Hard drawn steel wire.
- IS:1786-2008: Specification for High strength deformed steel bars and wires for concrete reinforcement.
- IS:2502-1963: Code of practice for bending & fixing of bars for concrete reinforcement.
- IS:2751 -1998: Recommended practice for welding of mild steel plain & deformed bars for reinforced construction.
- IS:5525 -1969: Recommendation for detailing of reinforcement in reinforced concrete works.
- IS:9077 -1979: Code of practice for corrosion protection of steel reinforcement in RB & RCC construction.
- SP:34 -1987: Handbook on concrete reinforcement detailing.
How is Storage of TMT Bars done?
Proper storing and handling of TMT steel bars, at every stage of its use, is extremely important, or it may result in damage to the bars. Damaged or corroded steel rebars, when reinforced with concrete, could affect the exhibition of the general construction. Any oversight concerning this could bring about a mishap later and be injurious to both life and property. While manufacturers must ensure proper handling and storage at their end, it is also important that builders take focus on this aspect as well. TMT bars at the building site must be taken care of in pre-characterized ways, beginning with dumping to lifting, stacking, cutting, twisting, fabrication and welding. Here are a few pointers regarding storing and handling the TMT bars to fortify the tensile strength of the concrete structures.
- Steel is reactive to moisture and dust.
- The stacking of the TMT bars should be altered for different diameters. Ensuring the right stacking height is vital to get it against sliding or collapse.
- Inappropriate stacking contrarily influences the rib design of the steel bar and will alter the surface attributes. This will eventually affect by and large the tensile strength of the TMT bar
- TMT bars must be categorized according to their length, ranging from 5.6mm to 32mm.
- For the perfect distribution of load, 1-2 meters of space must be maintained in between two bundles of TMT bars
- Excessive transverse and longitudinal load may harm the rib structure and altogether lessen the concrete bonding strength
- A raised wooden stage is required at the construction site, to forestall a direct contact with the mud-covered ground
- Categorically placed display boards help in identifying the required stack of TMT bars.
Leading brands that provide TMT Bars:
1. TATA TISCON
Tata Tiscon is also one of the top 10 TMT bar brands in India established in 1907 based in Mumbai. It is producing an annual crude steel capacity of over 28 million tonnes per annum among the global steel companies. Nowadays It is one of the world's most geographically-diversified steel producers with operations in 26 countries and a commercial presence in over 50 countries.
Steel Authority of India Limited (SAIL) is an Indian state-owned steel-manufacturing company based in New Delhi, India. It is a public sector undertaking, owned and operated by the Government of India with an annual turnover of ₹66,267 Crore for the fiscal year 2018-19 incorporated on 24 January 1974.
3. VIZAG STEEL
Rashtriya Ispat Nigam Ltd, (curtailed as RINL), otherwise called Vizag Steel, is a Public steel manufacturer based in Visakhapatnam, India. Rashtriya Ispat Nigam Limited (RINL) is the corporate entity of Visakhapatnam Steel Plant (VSP), India's first shore-based coordinated Steel Plant working with best-in-class innovation. Also, VIZAG is one of the top 10 TMT bar manufacturing companies in India.
4. JSW STEEL
JSW Steel is the leading business of the diversified US$ 13 billion JSW Group. JSW Steel, certified as “Great Places To Work in 2021”, is among the top 100 companies due to its great cultural foundation and good potential. Over the last three decades, it has grown from a single manufacturing unit to become India’s leading integrated steel company with a capacity of 28 MTPA in India & the USA (including capacities under joint control). Its roadmap for the next phase of growth includes a target of achieving 37.5 MTPA steel capacity by FY25. With a capacity of 12 MTPA, JSW Steel has the largest single location steel-producing facility in India at Vijayanagar, Karnataka.
5. JINDAL STEEL & POWER
Jindal Steel and Power Limited is an Indian steel and energy company based in Hisar. JSPL is a leading player in steel, power, mining, oil and gas, and infrastructure in India. Also, it is one of the top 10 TMT manufacturing companies in India.
6. KAMADHENU STEEL
Established in 1995, Kamdhenu Limited has been a pioneer in the concept of the Franchisee Model having attained success in the middle tier steel segment on a regional front. Their TMT Bars offer high ductility, better tensile strength, thermal resistance, and resistance to impacts of earthquakes.
7. SRMB STEEL
Being among the top 10 TMT bars in India, SRMB Steel is one of the leading primary steel producers or manufacturers in India and all over Asia. Based in Kolkata, the company was established in 1951. SRMB Srijan Pvt. Ltd. has a production capacity of approx 0.5 million tonnes per year with a turnover of ₹1500 cr., SRMB Steel has a large clientele including Indian Railways, NHAI, Indian Oil, Military Engineer Services, etc.
8. VISA STEEL
VISA Steel has set up esteem expansion offices at Kalinganagar Industrial Complex, Odisha in view of MoU endorsed with the State Government. The organization has set up a 150,000 TPA Ferro Chrome Plant at Kalinganagar. The offices incorporate 6 lowered Arc Furnaces with 3x25 MW Power Generating Units.
VISA Steel offers High Carbon Ferro Chrome according to International Quality Standards for end-use in Stainless Steel and Special Steel production Also, VISA is the top TMT manufacturing company in India.
9. ESSAR STEEL
ESSAR Group, established by Shashi Ruia and Ravi Ruia, in 1969, as a development organization, later enhanced into different core areas, to become one of India's greatest worldwide aggregates.
10. MESCO STEEL
Mideast Integrated Steel Ltd. (MISL) was incorporated in 1992 with resources in coastal Odisha in eastern India. It secured the Rodia iron ore mining lease in the prime iron ore belt of Odisha in 1996 and has a pig iron plant at Jaipur that was authorized in 2005. Being among the top 10 TMT bar companies in India, the company aspires to become the country’s major fully integrated steel company.
What are the tests done on TMT steel bars?
- Tensile Test - To measure the strength of reinforcement bars Universal Testing Machine (UTM) is used. Up to 32 mm capacity of TMT Bars can be tested without a machine as per IS 1786 and above which needs to be tested with it.
Therefore, Ultimate Tensile Strength = Ultimate Tensile Load (in KN) / Cross-Sectional Area (in mm2)
Bend and ReBend Test - The bending test should be conducted as per IS 1599 and using appropriately sized mandrels as specified in IS 1786. TMT bars should be bent at the midpoint to 180 degrees, following which one must check for cracks and fractures opposite to the bent side (which got the tension). It must be visible with normal or corrected vision. If there are no issues, the bar has passed the bend test.
In the re-bend test, the bending angle of the bar is kept at 135 degrees. Keep the TMT bar in boiling water at 100 degrees for 30 minutes, followed by cooling down the same. Once cooled, it is twisted again to 157.5 degrees and checked for rupture or cracks. The TMT bar shall be deemed to have passed the test if there is no rupture or crack visible at the bend portion (tension zone) to a person with normal vision.
It should be noted that both of these tests require expert supervision and can only be conducted at a laboratory.
TMT bars are one of the main construction materials that are broadly used for building earthquake-resistant structures. The ribbed TMT bars from the best TMT Bar producers provide better reinforcement to any concrete structure, thus, limiting damages during any seismic activities. The true genuine strength of a TMT bar lies in the ideal harmony among Toughness and Flexibility (Elongation). Choosing the Best TMT bars is one of the most important facts when it comes to choosing the right building materials.
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