TMT BARS.

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THERMO MECHANICALLY TREATED (TMT) BARS

DEPARTMENT OF CIVIL ENGINEERINGADICHUNCHANAGIRI INSTITUTE OF TECHNOLOGY

DEEPAKRAJ S.B.

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CONTENTSCONTENTS

1. INTRODUCTION1. INTRODUCTION

1.1 EMERGENCE OF STEEL1.1 EMERGENCE OF STEEL

2. STEEL AS REINFORCEMENT2. STEEL AS REINFORCEMENT

2.1 INTRODUCTION2.1 INTRODUCTION 2.2 STEEL BARS/ RODS FOR REINFORCEMENT2.2 STEEL BARS/ RODS FOR REINFORCEMENT 2.3 TYPES OF REINFORCING BARS2.3 TYPES OF REINFORCING BARS 3. THERMO-MECHANICALLY TREATED BARS3. THERMO-MECHANICALLY TREATED BARS 3.1 GENERAL3.1 GENERAL 3.2 PROPERTIES 3.2 PROPERTIES 3.3 INDIAN STANDARD SPECIFICATIONS FOR TMT BARS 3.3 INDIAN STANDARD SPECIFICATIONS FOR TMT BARS 3.4 THERMOMECHANICAL TREATMENT PROCESS3.4 THERMOMECHANICAL TREATMENT PROCESS 3.5 COMPARISON AND MERITS OVER OTHER PROCESSES3.5 COMPARISON AND MERITS OVER OTHER PROCESSES

3.5.1 PROCESSES3.5.1 PROCESSES 3.5.1.1 HOT ROLLING3.5.1.1 HOT ROLLING 3.5.1.2 COLD MECHNICAL WORKING3.5.1.2 COLD MECHNICAL WORKING 3.5.1.3 THERMO PROCESSING3.5.1.3 THERMO PROCESSING 3.5.2 COST SAVING3.5.2 COST SAVING 3.6 TEST TO IDENTIFY A GENUINE TMT BARS3.6 TEST TO IDENTIFY A GENUINE TMT BARS 3.7 ADVANTAGES3.7 ADVANTAGES 3.8 APPLICATIONS 3.8 APPLICATIONS

4. PRODUCTIONS4. PRODUCTIONS 4.1 QUALITY 4.1 QUALITY 4.2 AVAILABILITY4.2 AVAILABILITY 4.3 MARKETING4.3 MARKETING 4.4 NEW DEVELOPMENTS4.4 NEW DEVELOPMENTS

5. DISCUSSIONS5. DISCUSSIONS

6. REFERENCE6. REFERENCE

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IMPORTANCE OF STEEL AS REINFORCEMNT

•Tensile strength of concrete is very low, so reinforcement is required to resist tensile forces

•Reinforces the tension capacity of the concrete

•Resists not only tensile forces but also the compressive force as in the case of struts and columns

•It minimize the micro-cracking due to secondary effects such as shrinkage, creep, moisture and thermal variations

•More reinforcement doesn’t mean more strength hence proper designed quantity of steel based on analysis is must

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TYPES OF REINFORCING BARS PLAIN BARS

SQUARE TWISTED BARS

HOT ROLLED BARS

TORKARI BARS

CORROSION RESISTANT BARS

CTD BARS

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TMT BARS

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PROPERTIES

•FIRE RESISTANCEWithstand high temperature of the range 500ºC-600ºC - Ensures fire safety  

•DUCTILITYDue to high elongation and ductility TMT bars are highly seismic resistant - Hence preferred in earthquake zones 4&5 - Guarantee elongation well above 15%

•CORROSION RESISTANCEChemical composition along with TMT process avoids torsional residual stresses in the bar

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•WELDABILITYTMT bars do not suffer from loss of strength due excellent weldability - can be easily welded with CTD bars - No pre-heating or post-heating is necessary during welding

•OTHERS Toughness – Hardness - Excellent straightness – High strength - High fatigue resistance on dynamic loading

•BENDING Exhibit very high bendability and rebendabilty due to lower carbon content and higher elongation - Easier to work with TMT Bars due to easy bendability

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CONSTITUENT MAXIMUM PERCENT TMT(FE 415/FE 

500/FE 550)

TMT415

FE 415

TMT  500

FE  500

TMT550

FE 550

CARBON 0.25 0.3 0.25 0.3 0.25 0.3 0.2

SULPHUR 0.05 0.06 0.05 0.055 0.05 0.055 0.045

PHOSPHORUS 0.050 0.06 0.05 0.055 0.05 0.05 0.045

SULPHUR AND PHOSPHORUS

0.1 0.11 0.1 0.105 0.1 0.1 0.09

CORROSION RESISTANT ELEMENTS

- - - - - - 0.75 MIN

CARBON EQUIVALENT

- - - - - - 0.53 MAX

INDIAN STANDARD SPECIFICATIONS FOR TMT BARS IS-1786 (1985)

TABLE-1

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PROPERTY GRADE

FE 415 TMT415

FE500

TMT500

FE550

TMT550

0.2 percent proof stress/yield stress Min N/mm.sq.

415 415 500 500 550 550

Elongation.percent Minimum,on gauge length 5.65.Square Root (A) where A is the cross-sectional area of the test piece

14.5 22(Up to

28mm dia) 20

(Above 28 mm dia)

12 20(Up to

28mm dia) 18

(Above 26 mm dia)

8 18(Upto 25 mm dia) 16(Above 28 mm dia)

Tensile Strength,Min

10% more than the actual 0.2% proof stress but not less than 485 N/mm.sq

10% more than the actual 0.2% proof stress but not less than 500 N/mm.sq

8% more than actual 0.2% proof stress but not less than 545 N/mm.sq

8% more than actual 0.2% proof stress but not less than 580 N/mm.sq(Upto 28mm dia)560 N/mm.sq.)(above 28 mm dia)  

6% more than the actual0.2% proofstress but not less than 585 N/mm.sq.  (Upto 28mm dia) & 560 N/mm.sq.)(above 28 mm dia)

6% more than the actual0.2% proofstress but not less than 630 N/mm.sq. (Upto 28mm dia) & 610 N/mm.sq. (above 28 mm dia)

Upto 28mm dia) & 560 N/mm.sq.)(above 28 mm dia)

TABLE-2

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TMT PROCESS Advanced heat treatment technique - Red hot rebars with controlled water quenching – TMT process helps to produce reinforcement bars of high strength, superior ductility, weldability, bendability and thermal resistance

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Outer surface of bars becomes colder while the core remains hot – Development of temperature gradient in the bars – After being taken out the heat flows from the core to the outer surface - Causes further tempering of steel bars – Steel attains higher yield strength

Soft core of ferrite-pearlite with strong and tough case of martensite

CORE

OUTER PERIPHERY

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CTD vs TMT

•Cold twisting and drawing•Ductility greatly reduces due to cold working •Weldability is inconsistent •High strength is affected at high temperature at welding

•Controlled quenching and tempering•Ductility is excellent•Weldability is consistent•Strength bound to increase due to TMT process

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COST SAVING IN STEEL – A MERIT OF TMT

Dimension of the section (mm)

Mu

(kN-m)

Fck Grade steel

Area of steel(mm2)

No. & dia. of bars %

saving with

respect to

Fe415

Ast Asc Tension Comp

Mu = 300Mu = 300

Mu / bdMu / bd22 = 4 = 4

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Fe415 2063 9604-20# + 4-6#

9-12# ---

Fe500 1710 7884-20# + 3-6#

7-12# 17.3%

Fe550 1545 7284-20# + 2-6#

7-12# 24.8%

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Fe415 2130 5554-20# + 5-6#

5-12# ---

Fe500 1763 4654-20# + 3-6#

5-12# 17.0%

Fe550 1613 4204-20# + 3-6#

4-12# 24.2%Use of TMT bars leads to higher strength that leads to saving in material, reduction in cost and so lower dead load on structures

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TEST TO IDENTIFY A GENUINE TMT BAR -Helps to understand the characteristics of TMT bars

-Necessary to differentiate standard and fake TMT bars which are elusive

-Involves •Cutting a TMT bar

•Smoothening of the cross section to a fine polished state by grinder and emery paper

•Pickling smooth end of sample in nitrol solution (10% nitric acid with 90% ethyl alcohol)

•Resulting in uniform tempered martensite periphery with a softer core (an yardstick in testing originality of TMT )

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Improper quenching all round the periphery-Should be avoided-

-Uniform and concentric hardened periphery and the softer core-Possess tensile strength coupled with high elongation as required in seismic zone.

-Uniform tempered martensite periphery -Hardened periphery will be about 30% of the bar cross sectional area-Ideal rebar for civil construction

TEST RESULTS

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-Uniform cross section of hardened periphery with a soft core -Excellent for civil construction.

Possess bad quenching and tempering - quenching is not uniform -

Not good for civil construction -

Over quenching- Exhibit high yield strength and very poor ductility -

Should never be used in civil construction-

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ADVANTAGES -Better ductility and weldability

-Better yield strength, tensile strength and percent elongation

-Easy bendability and thus require less energy for bending and

rebending

-Ability to resist loss of strength at higher temperatures

-Saving of more than 15 percent in steel consumption

-Better corrosion resistance

-Superior product with consistent properties

-Easy manufacture of different strengths of rebars

-Fatigue resistance

-Ideal choice for seismic zones due to excellent ductility properties

-Possible to dispatch customers almost immediately after rolling is

complete

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APPLICATIONS •By virtue of various engineering properties TMT bars can be used for Residential Buildings, Bridges, and Industrial Establishment

•In Steel-concrete composite construction which involves one or more of steel concrete composite elements i.e. composite beam, composite slab and composite columns •Because of corrosion resistance TMT bars are employed in construction exposed to coastal, marine or underground environment

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QUALITY

1. Minimum yield strength 415 N/mm2

2. Minimum tensile strength 10% more than yield strength subject to

minimum 560 N/mm2

3. Minimum elongation 16 (generally 18 to 22).

4. Stress ratio (Ts / Ys) 1.10(generally 1.15 to 1.25)

5. Weldability

6. Bar temperature of 850-900 ± (30-40) degrees in the cooling tube

7. Required technology in plants

FACTORS CONSIDERED TO ENSURE QUALITY

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AVAILABILITY-Obtainable in strengths of 415, 500 and 550 MPa

-Renowned manufactures are SAIL, TISCO, IISCO,RINL and,

VIZAG STEEL PLANT etc

-Available brands of TMT bars are SAIL TMT, SAIL TMT HCR,

VIZAG TMT

-THERMEX, TEMPCORE are available as international brands

-Available in bar diameter ranging from 8mm - 40mm

-Available in standard lengths & specific lengths

up to a length of 20m

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PRODUCTION

-Requires huge investments, expertise and stringent process

-Production of about 1.5 million tones each year by major plants

-By 2010 TMT bars constitute 80 to 85% of the rebars made in the

country against the present 50 to 55%

-The Q&T rebars will become the preferred choice

-Production of untreated re-bars being offered as

TMT bars in market

NEW DEVELOPMENTS

-Emergence of CRS in a view to increase corrosion resistance

-Production of sophisticated silicon steel

-Introduction of Fe 600 TMT bars

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INFERENCE•With its versatility TMT bars overtook CTD bars

•Great concern on non-availability of quality TMT bars

•Vital factors are raw materials, rolling mill and treatment process

•Thorough examination for requisite properties andverification of source to test originality

•Fulfilling above factors guarantee quality TMT bars

•Encourage clients and users to go for TMT bars

•Make use of stupendous qualities of TMT bars should be the order of the day

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REFERENCEREFERENCE11 Dr.C.S.Vishwanatha, “History in prospective- A journey through Dr.C.S.Vishwanatha, “History in prospective- A journey through Indian reinforcing bars”, The Indian concrete journal, Jan 2004, vol.78, Indian reinforcing bars”, The Indian concrete journal, Jan 2004, vol.78, pp14-18 pp14-18 22 Dr.S.R.Mediratta, “Steel reinforcement-Demand, quality and new Dr.S.R.Mediratta, “Steel reinforcement-Demand, quality and new application in India”, The Indian concrete journal, Jan 2004, vol.78, pp.9-13.application in India”, The Indian concrete journal, Jan 2004, vol.78, pp.9-13.33 Dr.P.Dayaratnam, “Guest editorial comments”, The Indian concrete Dr.P.Dayaratnam, “Guest editorial comments”, The Indian concrete journal, Jan 2004, vol.78, pp.3-4.journal, Jan 2004, vol.78, pp.3-4.44 Dr.C.S.Vishwanatha, “The ABC of TMT bars”, The Master builder, Dr.C.S.Vishwanatha, “The ABC of TMT bars”, The Master builder, Oct-Nov 2004, vol.6, pp.41Oct-Nov 2004, vol.6, pp.4155 HY-TUF STEELS PVT LTD,HY-TUF STEELS PVT LTD, www.hytuf.comwww.hytuf.com66 Jagvir Gaoyal, “Latest Developments on steel front”, Jagvir Gaoyal, “Latest Developments on steel front”, www.tribuneindia.comwww.tribuneindia.com77 Kaushik.S.K. and Singh.B. “Influence of steel-making processes on Kaushik.S.K. and Singh.B. “Influence of steel-making processes on the quality of reinforcement”, The Indian concrete journal, July 2002, vol.76, the quality of reinforcement”, The Indian concrete journal, July 2002, vol.76, pp.407-412.pp.407-412.88 Prabir C, Basu, Shylamoni P and Roshan A.D, “Characterization of Prabir C, Basu, Shylamoni P and Roshan A.D, “Characterization of steel reinforcement for RC structures, An overview and related issues”, The steel reinforcement for RC structures, An overview and related issues”, The Indian concrete journal, Jan 2004, vol.78, pp.22 Indian concrete journal, Jan 2004, vol.78, pp.22 99 Mary Land Metrics, http.mdmetric.comMary Land Metrics, http.mdmetric.com1010 SAIL, www.sail.co.inSAIL, www.sail.co.in

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THANK YOU ALL