1 TMT bars
Nov 01, 2014
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TMT bars
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Reinforcement bars Overview
In order to fulfill industry need to make construction faster and economical, reinforced concrete structures replaced earlier building styles.Steel reinforcement was done with a view to supplement the weak tensile strength of concrete.
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Overview Reinforcing was done with
Plain steel bars till 60’s Low strength Low surface area resulting poor grip
CTD bars replaced plain steel bars in 60’s
High strength Larger area of projection to ensure better
grip, but Non uniform strength Low ductility due to work hardening Low resistance to corrosion
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Overview
TMT Bars introduced in 70’s to overcome shortcoming of CTD bars.
These are produced using new technology to ensure higher strength, better ductility, and resistance to corrosion.
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Reinforcement bars Overview
Methods for increasing Yield Strength
As Rolled TMT Cold Deformed
Increase % C,Mn
Addition of Nb, V
Weldability Cost
Heat Treatment from the heat of Rolling
Improved Quality
Twisting, Drawing, Cold Rolling
Work Hardening and residual stress
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Process Overview TMT process is producing desired
mechanical properties in a bar using heat treatment
Rolls
Rolls
Water Quenching
Water Quenching
Bar under Rolling
Cooling Bed
Bar under Cooling
TMT Bundles
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Process
In TMT process bars are produced by rapid cooling of steel being rolled. This produces hardened structure called “tempered Martensitic steel” on the outer surface, while inner core remains soft “Ferritic Pearlitic steel.”
The combination of these two factors gives excellent yield strength to the bar along with superior ductility & weldability.
Ferritic Pearlitic steel
tempered Martensitic steel
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Product Advantages In the past, the conventional ribbed cold
twisted bars were used in RCC structures. The bars had inherent problems of poor weldability & ductility. Additional operation of cold twisting induced residual torsional stresses and became less corrosion resistant due to stresses and removal of preventive mill scale coating.
TMT process eliminates all these undesirable attributes. They attain higher strength, excellent ductility, bendability and superior weldability due to lower carbon content.
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Features & Benefits Lower carbon content and made from
fully killed steel. Higher yield strength, ultimate tensile
strength, % elongation when compared to CTD bars of same grade.
Easy bendability, weldability and ductility ensures economy and safety in use.
In-built ability to resist loss of strength at higher temperature.
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Features & Benefits
Require less energy for bending and re-bending along with superior reverse bending properties.
Can be butt or lap welded. Use of Fe 500 grade results in up
to 15 % saving in steel consumption.
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Applications
TMT bars can be used in all the applications of reinforced cement concrete structures, where the soil possesses corrosive characteristics due to salinity owing to excellent corrosion resistance or under seismic conditions because of their higher energy absorbing capacity.
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