A detailed presentation by Happho on Reinforcement steel and its detailing, Types of steels, What is Rebar Steel, Field Tests for Steel, Bar Bending Schedule, Best Practices for Placing Reinforcement etc., . Rebars are available in the following grades as per IS:1786-2008 FE 415/500/500D www.happho.com is a One Stop Solution for Bungalow Construction, Interiors & Renovation, and an Online Marketplace for Construction Materials.

1. REINFORCEMENT STEEL AND ITS
DETAILING
Vinod Kumar Singh
Co-Founder, Happho.com
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www.happho.com is a One Stop Solution for Bungalow Construction, Interiors & Renovation
and an Online Marketplace for Construction Materials

2. INTRODUCTION
•It is widely appreciated that steel reinforcement plays a critical role in influencing the
structural behaviour of RCC members .
• Strong in tension and at the same time ,ductile enough to be shaped or bent.
• Thermal expansion of both steel (0.0000117 / 0
C) and concrete are approximately same.
• Bonds well with concrete (When concrete sets and hardens, its shrinks causing the steel
embodied in it to be held firmly and thus preventing any relative movement between the
two material)
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3. •Most engineers tend to take the properties of reinforcement for granted and more often
than not remain ignorant about the influence of the metallurgical and production
characteristics on the mechanical properties of steel.
•Given the liberalised import regime and the large-scale conversion of imported scrap in
the form of scrap rails, automobile scrap, defence scrap, scrap from ship breaking, etc of
unknown or unsuitable quality, into steel rebars, possibly under less-than controlled
conditions, raises apprehensions about the quality and reliability of steel rebars used in the
construction industry.
•To be able to take informed decisions about the quality of steel rebars in a holistic
manner, it is imperative that engineers are conversant with the steel characteristics that
have a bearing on the mechanical properties of the rebars
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INTRODUCTION

4. Introduction to Iron and Steel
•Iron: Iron is an element and can be pure.
•Cast iron: Iron that contains about as much carbon as it can hold which is
about 4%.
•Wrought iron: Iron that contains glassy inclusions.
•Steel: Iron with a bit of carbon in it, generally less than 1%.
•Pig iron: Raw iron, the immediate product of smelting iron ore with coke and limestone in a
blast furnace. Pig iron has a very high carbon content, typically
4-5%, which makes it very brittle and not very useful directly as a material.
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INTRODUCTION

5. STEEL PRODUCTION
Materials used to produce pig iron
•Coal—as coke—used to supply carbon. In a blast furnace, ore is heated in the presence of
Carbon—this allows oxygen in the ore to react with carbon to form gases.
• Limestone—Helps to remove impurities
•Iron ore—Processed ore at the start of the process has about 65% iron.
•Impurities (slag) float on the top of melt.
1.0 ton of steel requires about 3.2 tons of raw materials to produce
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INTRODUCTION

6. • Rebars are rolled from billets
Manufacture of billets are carried by Open hearth, electric, duplex or a combination
of these process
• Billets are produced either from iron ore through the blast furnace converter route,
or by melting scraps and refining the same in the furnace (re-rollables).
• Ribs are indented on the surface of the deformed bars during process of rolling.
(HYSD bars have ribs on the surface and this increases the bond strength at least by
40% )
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REINFORCEMENT STEEL – PRODUCTION PROCESS

7. • Plain Mild steel of grade Fe-250 were widely used till 1967.
• Square twisted bars (deformed bars) were first introduced in India in 1965.
• Cold Twisted deformed Bar (CTD) – produced by cold working process, basically a
mechanical process.
It involves stretching twisting of mild steel, beyond the yield plateau and
subsequently releasing the load.
Yield strength in the range of 405 MPa
• High Strength Deformed Bar
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REINFORCEMENT STEEL - TYPES

8. 8
REINFORCEMENT STEEL - TYPES

9. • TMT – Introduced in India in 1980s
Thermo mechanical treatment is advanced heat treatment process in which hot bars
coming out of last rolling mill stand are rapidly quenched through a series of water
jets.
Rapid quenching provides intensive cooling of surface with hot core. The rebar are
then allowed to cool in ambient temperature. During the course of such slow
cooling, the heat released from core tempers the hardened surface while core is
turned in the ferrite-pearlite aggregate composition.
TMT process thus changes the structure of material to a composite structure of
ductile ferrite-pearlite composition with tough surface rim of tempered martensite
providing an optimum combination of high strength, ductility, bendability.
These bars have very good weldability and do not suffer from loss of strength at the
weld joints and can be easily welded with CTD bars
Four grade of rebar are presently available in India for structural use. The rebar are
graded according to their specified yield strength.
Fe415, Fe500 ,Fe550 & Fe600
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REINFORCEMENT STEEL – TMT STEEL

10. PROPERTY Fe415 Fe415D Fe500 Fe500D Fe550 Fe550D Fe600
0.2% Proof Stress/Yield
strength ,Min,MPa
415 415 500 500 550 550 600
Elongation %, Min 14.5 18 12 16 10 14.5 10
Tensile Strength,Min.MPa 10% more
than actual
0.2% proof
stress,min
yield stress
485
12% more
than actual
0.2% proof
stress,min
yield stress
500
8% more
than actual
0.2% proof
stress,min
yield stress
545
10% more
than actual
0.2% proof
stress,min
yield stress
565
6% more
than actual
0.2% proof
stress,min
yield stress
585
8% more
than actual
0.2% proof
stress,min
yield stress
600
6% more
than actual
0.2% proof
stress,min
yield stress
660
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REBAR STEEL – PHYSICAL PROPERTIES

11. Terminology:
•Elongation – The increase in length of tensile test piece under stress. The elongation at
fracture is conventionally expressed as a % of the original gauge length of standard test
piece.
•0.2% Proof Stress : The stress at which a non proportional elongation equal to 0.2% of the
original gauge length takes place.
•Tensile strength : The maximum load reached in a tensile test divided by the effective cross
sectional area of the gauge portion of the test piece(also termed as Ultimate Tensile
strength.
•Yield strength = Stress (that is, load per unit cross-sectional area) at which elongation first
occur in the test piece, without increasing the load during the tensile test. In the case of
steels with no such definite yield point, proof stress shall be applicable.
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REBAR STEEL – PHYSICAL PROPERTIES

12. Stress – Strain Relation
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REBAR STEEL – PHYSICAL PROPERTIES

13. CONSTITUENTS
%,MAX
Fe415 Fe415D Fe500 Fe500D Fe550 Fe550D Fe600
CARBON 0.3 0.25 0.3 0.25 0.30 0.25 0.3
SULPHUR 0.06 0.045 0.055 0.040 0.055 0.040 0.040
PHOSPOROUS 0.06 0.045 0.055 0.040 0.050 0.040 0.040
SULPHUR &
PHOSPOROUS
0.11 0.085 0.105 0.075 0.100 0.075 0.075
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REBAR STEEL – CHEMICAL PROPERTIES

14. CHEMICALS CONTROLLING
PROPERTY
ACTUAL EFFECT
CARBON Hardness, strength,
weldability and
brittleness
High carbon content contributes to the tensile strength of steel.
Lower carbon content less than 0.1% will reduce strength. High
carbon content of 0.3% and above makes the steel bar unweldable
and brittle.
SULPHUR Present as an
impurity which
increases its
brittleness.
Presence of sulphur should be limited as per IS 1786.Higher sulphur
makes bars brittle.
PHOSPOROUS Present as an
impurity which
increases strength &
brittleness.
High phosphorous content contributes to the increase in strength and
corrosion resistance properties but brings brittleness.
Influence of different chemical ingredients in steel on properties of rebars.
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REBAR STEEL – CHEMICAL PROPERTIES

15. • Test certificate will confirm the compliance of quality of supplied materials as per the
requirement of relevant Indian standard code.
•Steel bundle should have tag giving detail of the Batch/lot detail.
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STEEL RECEIPT AT SITE

16. • Rolling Margin – Weight per meter
For any steel reinforcement bar, weight per running meter is equal to d2/162 Kg,
where d is diameter of the bar in mm. For example, 10 mm diameter bar will weigh
10x10/162 = 0.617 Kg/m.
Tolerances on nominal mass
Dia of bar
(mm)
Tolerance in nominal mass
(%)
Upto & including 10mm +/- 7
Over 10mm & upto 16mm +/- 5
Over 16mm +/- 3
With negative rolling margin a saving on 7% on steel can be achieved
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STEEL – FIELD TEST

17. • Bend Test
Specimen Shall be doubled over the mandrel by continuous pressure until sides are
parallel.
If there is no rupture or crack visible, the specimen shall be considered to have passed
the test.
• Rebend Test
The test piece shall be bent to an included angle of 135 0
using mandrel of appropriate
dia.
The piece shall be aged by keeping in boiling water for 30mins & allowed to cool.
The piece shall then be rebend to have an included angle of 157 ½ 0
If there is no rupture or crack visible, the specimen shall be considered to have passed
the test
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STEEL – FIELD TEST

18. • Transverse reinforcement:
Transverse reinforcements are very important. They not only take care of structural
requirements but also help main reinforcements to remain in desired position. They
play a very significant role while abrupt changes or reversal of stresses like earthquake
etc.
They should be closely spaced as per the drawing and properly tied to the
main/longitudinal reinforcement.
• Lap length or development length :
Lap length is the length overlap of bars tied to extend the reinforcement length.. Lap
length about 50 times the diameter of the bar is considered safe. Laps of neighboring
bar lengths should be staggered and should not be provided at one level/line. At one
cross section, a maximum of 50% bars should be lapped.
In case, required lap length is not available at junction because of space and other
constraints, bars can be joined with couplers or welded (with correct choice of method
of welding).
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TERMS RELATING TO STEEL DETAILING

19. • Anchorage length:
This is the additional length of steel of one structure required to be inserted in other at
the junction. For example, main bars of beam in column at beam column junction,
column bars in footing etc. The length requirement is similar to the lap length or as per
the design instructions.
• Development length:
Development length is defined as minimum length of bar in which the bar stress can
increase from zero to the yield strength. If the distance is less than the development
length the bar will pull out the concrete. The development length is a function of yield
stress, bar diameter, average bond stress at surrounding concrete.
(bond consist of adhesion due to the colloidal action in cement & also due to friction
between steel & Concrete.)
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TERMS RELATING TO STEEL DETAILING

20. • Bent up bars:
it is actually economization of material. normally, for fixed ended beams positive
(sagging) moments are present at the mid span and negative (hogging) moments at the
supports .so bottom steel is required at the mid span and top steel resists negative
moments at the supports. a bent-up is provided to take the steel on the top at
supports, as bottom steel is not normally required at the supports
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TERMS RELATING TO STEEL DETAILING

21. • Bar-bending-schedule is the schedule of reinforcement bars prepared in advance
before cutting and bending of rebars. This schedule contains all details like size, shape ,
number of bars and dimension of rebars to be cut.
Sl.No Type of bar and
mark
Shape No. Length in m Weight
per unit
length
in Kg
Weight
in Kg
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BAR BENDING SCHEDULE

22. •Generally Engineers don't consider increase in steel length (bend allowance) for each
bend to arrive at cutting length
•Typically 2d for 12mm bar dia & 1d for higher dia should be considered for every bend.
(Fixing & Reconciliation is highly affected if above allowance is not considered)
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BAR BENDING SCHEDULE

23. 23
BAR BENDING SCHEDULE

24. 2424
Work Procedure For Fixing Reinforcement

25. • Ensure reinforcement brought to site is from approved /tested lot (Quality Control
Department should ensure)
• Reinforcement brought to the site, should be clean and free from rust, mud, oil, grease
paint or any foreign deleterious material present on the surface
• Bar bending schedule to be made as per Good For Construction (GFC) drawing and duly
checked by Project Manager, after his approval cutting and bending should begin
• Formwork to receive the reinforcement should be clean & free from debris
• Ensure that the size of bar, spacing between bars, correct bends, proper laps,
curtailment of bars, tying of binding wire, enough chairs kept in proper position and
cover blocks are all in order.
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Work Procedure For Fixing Reinforcement

26. • Dowel Bars should not be inserted into placed concrete.
• Reinforcement should be placed and tied in such a way that concrete placement be
possible without segregation of the mix. Re-bar spacing to be adjusted (temporary) to
ease insertion of needle.
• Numbers of laps and chairs to be recorded on BBS as per actual placed at site.
• Use of mechanical splicing should be approved by RCC consultant. They should be
provided as far as possible away from the section of maximum stress.
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Work Procedure For Fixing Reinforcement

27. 27
Mechanical Splice
Conventional
Bar Lapping
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Work Procedure For Fixing Reinforcement

28. 28
Mechanical Couplers
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Work Procedure For Fixing Reinforcement

29. General Points/Precautions
1.Care shall be taken to see that starter is not damaged while tying column
reinforcement. Normally column reinforcement fixing is started on next day of column
starter casting. Or if required first tie column reinforcement and than cast starter by
lifting few bottom rings to facilitate concreting of starter
2.Top ring shall not be half inside the concrete and half outside the concrete as seen in
picture. It shall be 40mm below top of concrete. Same to be ensured for column starter
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Work Procedure For Fixing Reinforcement

30. 3. All hooks or stirrups of RCC member to be bend to 45 degree, fitter can use tool shown
in picture.
Hook bend AT 45 Deg. Tool to bend
3030
Work Procedure For Fixing Reinforcement

31. 4. No binding wire knots shall protrude in cover zone.
5. General Consumption of Binding wire should be 9 to 12 Kg/MT –
Residential Building/Podium (regular slab)
3131
Work Procedure For Fixing Reinforcement

32. 6. Provide stirrups about 600mm above shuttering top so that needle vibrator can be
inserted without any kind of obstructions
7. Provide Master rings at every 1m in the column.
3232
Work Procedure For Fixing Reinforcement

33. 8. Do not tie stirrups above concreting level, since they will obstruct flow of concrete.
3333
Work Procedure For Fixing Reinforcement

34. Conclusions
• Steel reinforcements are like a skeleton in human body. Plain concrete without steel or
any other reinforcement is strong in compression but weak in tension. Steel is one of
the best forms of reinforcements, to take care of those stresses and to strengthen
concrete to bear all kinds of loads.
• To be able to take informed decisions about the quality of steel rebars in a holistic
manner, it is imperative that we are conversant with the steel characteristics that have
a bearing on the mechanical properties of the rebars
• Understanding reinforcement steel in totality help us exploits its various
characteristics, for delivering a duarble end product.
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