TMT bars of grade Fe-500D and Fe-550D are preferred for high-rise construction

The high strength and ductility of these TMT bars make them the most preferred choice for high-rises says Shailesh Bhandari, Managing Director, Electrotherm India Ltd.

What kind of load bearing capacity are TMT bars utilized in high-rises required to have?

Due to height and load of high rises, it is necessary to withstand the lateral forces imposed on it in its lifecycle as also earthquakes. So, major factors to be taken care of are:-

• Structural integrity & strength
• Thermal resistance
• Corrosion resistance

The Yield Stress (YS) & Ultimate Tensile Strength (UTS) of TMT bars are important parameters to understand the strength and hardness of TMT bars. YS & UTS are the characteristics of TMT bars which denotes the total load bearing capacity of the TMT bars in Fe-500D and Fe-550D grade.

Achieving the above mentioned two parameters requires control quenching and refined steel making process . ET (Electrotherm) adopted the process route BF+DRI – IF – LRF for getting refined steel to make TMT bars of grade FE-500D and Fe-550D. Thereby it is safe to say that ET TMT bar possesses all the characteristics which are required in high-rise buildings.

Apart from high yield strength, what kind of qualities are required in TMT bars when it comes to bonding and ductility?

Apart from yield strength,  TMT bars require ultra design rib pattern, both longitudinal and transverse rib for efficient bonding. Thees are designed using superior CNC notch cutting machines to ensure consistent rib patterns and optimum rib depths.

For excellent ductility of TMT bars, control chemical composition and control quenching is required to achieve high % Elongation and UTS/YS ratio. The microstructure of TMT bars from quenching system is very important to provide TMT bar with a soft ferrite & pearlite fine grained inner core and a strong & tough tempered martensite outer layer imparting it with high ductility as well as strength thus making it ideal for high rises building.

ET maintains all these properties by using advanced Thermex quenching process and using process control of advanced PLC system to maintain ring area (15%-25%), minimum 18% of Elongation and UTS/YS ratio must be greater than equal to 1.15.

How can TMT bars be made resistance to corrosion?

TMT bars can be made corrosion resistant through certain techniques:-

• By addition of a low alloy element (Chromium, Copper, Phosphorous and Nickel) during steelmaking to make TMT bars of grade CRSFe-500 & CRSFe- 500D which is more effective for corrosion resistance.
• In areas with high moisture content, surface of TMT bars are also coated with

       Zinc coat make them more corrosion-resistant.

• Fusion Bonded Epoxy Coating is used to protect TMT bars from corrosion. Epoxy coating of thickness 100 micron to 300 micron (IS 13620) is uniformly applied on the surface of TMT bars. Due to the protective film, epoxy coated TMT bars last longer and add to the quality of the construction having better bonding with cement and concrete.
• Out of these three techniques, fusion bonded epoxy coating is most popular as it is easy to apply and also cost effective.
• ET conducted a performance evaluation from CSIR-CECRI Karaikudi (SSP 13/19- Interim Report) and found that life of epoxy coated bars are 3 to 4 times longer than normal TMT bars.

What products do you offer especially for high rises?

For high rises structures, TMT bars of grade Fe-500D and Fe-550D are preferred because of high strength and excellent ductility.

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