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FAQs >
Reinforcement |
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Q.
What is steel reinforcement? Why is it required in a concrete
structure?
Steel reinforcements are used, generally, in the form of bars of
circular cross section in concrete structure. They 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. |
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Q.
What is bar-bending-schedule?
Bar-bending-schedule is the schedule of reinforcement bars
prepared in advance before cutting and bending of rebars. This
schedule contains all details of size, shape and dimension of
rebars to be cut. |
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Q.
What are the different types of steel reinforcements being used
in a reinforced concrete structure?
Mild steel bars conforming to IS: 432 (Part I) and Cold-worked
steel high strength deformed bars conforming to IS: 1786 (grade
Fe 415 and grade Fe 500, where 415 and 500 indicate yield
stresses 415 N/mm2 and 500 N/mm2 respectively) are commonly
used. Grade Fe 415 is being used most commonly nowadays. This
has limited the use of plain mild steel bars because of higher
yield stress and bond strength resulting in saving of steel
quantity.
Some companies have brought thermo mechanically treated (TMT)
and corrosion resistant steel (CRS) bars with added features.
Bars range in diameter from 6 to 50 mm. Cold-worked steel high
strength deformed bars start from 8 mm diameter. For general
house constructions, bars of diameter 6 to 20 mm are used. |
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Q.
Why cover blocks are required to be placed before concreting?
What are their sizes?
Cover blocks are placed to prevent the steel rods from
getting exposed to the atmosphere, and to place and fix the
reinforcements as per the design drawings. Once the steel is
exposed to the atmosphere, corrosion starts. Sometimes it is
commonly seen that the cover gets misplaced during the
concreting activity. To prevent this, tying of cover with steel
bars using thin steel wires called binding wires (projected from
cover surface and placed during making or casting of cover
blocks) is recommended. Covers should be made of cement sand
mortar (1:3). Ideally, cover should have strength similar to the
surrounding concrete, with the least perimeter so that chances
of water to penetrate through periphery will be minimized.
Provision of minimum covers as per the Indian standards for
durability of the whole structure should be ensured.
Shape of the cover blocks could be cubical or cylindrical.
However, cover indicates thickness of the cover block. Normally,
cubical cover blocks are used. As a thumb rule, minimum cover of
2” in footings, 1.5” in columns and 1” for other structures may
be ensured. |
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Q.
How important are transverse reinforcements like links and
stirrups? What precautions should be taken while tying them?
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. |
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Back to Questions |
Q.
What is a lap or development length? Where and how should they
be provided?
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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| Q.
What is 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 mentioned in previous question or as per the design
instructions. |
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Q.
What is the checklist for steel reinforcement before the
placement/pour of concrete?
Reinforcement should be free from loose rust, oil paints, mud
etc. it should be cut, bent and fixed properly. The
reinforcement shall be placed and maintained in position by
providing proper cover blocks, spacers, supporting bars, laps
etc. Reinforcements shall be placed and tied such that concrete
placement is possible without segregation, and compaction
possible by an immersion vibrator. |
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Q.
For a given diameter, how do we calculate the weight of steel
per meter length of the steel bar and vice versa?
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. |
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Q.
Can we receive the quality test certificate of steel from the
supplier?
Yes. We can receive the test certificate of the batch of
materials supplied at our site. The certificate will confirm the
compliance of quality of supplied materials as per the
requirement of relevant Indian standard code. |
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