230040117-Tmt-Tor-Steel-Rebars.pdf - econference(1)_...

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1econference(1), BREINSBuilding Research Institute (P) Ltd,,30MARCH2010econference(1)_______________________________________________________Q. Which high strength deformed steel rebar is better for RC Construction?TOR steel (Fe 415) or TMT (Fe 500)CommentsThese days, high yield strength deformed(HYSD) TOR 415 & TMT 500steel rebars arewidely used in the construction of Reinforced Concrete (RC)structures. Following majorparameters should be checked & compared while determining the quality of any steelrebars;Tensile StrengthDuctilityBendabilityWeldabilityDurabilityBehavior Under Cyclic LoadingAt first, the manufacture process and configuration of the TOR & TMT Steel rebars should bethoroughly understood which have been described in detail below;(A)Manufacture Process and ConfigurationTOR RebarsConventionally, Rebar’s are produced by two different methods of production. In the firsttype, the bars possessing ribs at their surface are hot rolled from steel billets along withdefinite chemical composition to achieve desired strength.Another one is produced by “Cold Working Process” that involves the stretching andtwisting of the Mild Steel (MS) bar of250 MPain a repeated manner. Rebars such producedareCold Twisted Deformed (CTD)rebarsOn loading, Steel will follow a linear elastic path similar to that of original mild steel till itreaches the point where unloading starts; which also becomes a new “yield point”. Pleaserefer FIG1. The required increase in yield strength is achieved by appropriate selection ofunloading point. These rebars are commercially manufactured under the trade name of“TOR Steel”. TORSteel of Fe 415 grade is widely manufactured in our country.
2econference(1), BREINSBuilding Research Institute (P) Ltd,,30MARCH2010FIG1 (Typical StressStrain Curve for Mild Steel Rebars; Showing Loading /Unloading Path)TMT RebarsTMT stands for“Thermo Mechanically Treated”steel rebars are produced by applyinglatest advanced technologies resulting in far more superior properties than conventionalCTD /TORrebars.Thermo mechanical treatment is an advanced heat treatment process in which hot barscoming out of last rolling mill stand are rapidly quenched by a special water spray system.Rapid quenching provides intensive cooling that converts surface layer of the bar toahardened structure called “Martensite” and with hot core; austenitic.FIG2, (Longitudinal View of TMT Steel Rebars)
3econference(1), BREINSBuilding Research Institute (P) Ltd,,30MARCH2010The rebars crosssection with a temperature gradient is then allowed to cool in ambientconditions called “Self tempering”. Upto this stage temperature of core is higher than thatof the surface. Heat is then allowed to flow from the core to the surface resulting intempering of the surface that gives outer surface a strength and toughness while core isturned into a “Ductile Ferrite Pearlite”.

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Term
Spring
Professor
N/A
Tags
Building Research Institute, TMT 500

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